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Sky Watchers' Guide

boy looking up at the sky with his binoculars

This user-friendly material explains in simple terms the basics of weather.  It's filled with fast facts, activities, and experiments to help you help them.  You can use this guide as a stand-alone resource, or you can join in the program and make science class the best part of your students' day!

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Chapter 1 - First Steps

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Setting Up Your Weather Station


Tips 1.1

At various points through this Guide, you will be given complete instructions for the students to create a home-made equivalent for most of these instruments.

The full Watchers kit contains a complete suite of weather instruments as well as log sheets for recording your observations. If you have acquired weather instruments from another source, you can still print copies of the log sheets and graph forms from the Teachers' Corner on our Web site which links from the side menu at Canadian Weather.

This chapter will focus on helping you set up these instruments so that your students can begin taking weather observations right away. The regular observing and reporting of weather will reinforce what they learn in class.


The barometer measures air pressure, or the weight of a column of air above a given spot, such as your school. Generally speaking, when the air pressure rises, it means fair weather is approaching and when the air pressure falls, it means unsettled weather is approaching.

But this is not always the case as you will discover during your year as a Sky Watcher. Please use caution in applying the weather terms -- stormy, rain, change, fair and very dry -- which are written on the barometer. Rely instead on the numeric readings for the day and the trends that you will see in successive readings.

Before you use the barometer for the first time, set it to the mean sea level pressure for your area. You only have to do this once. There are several ways to get the current reading for air pressure in your town or city:

  • watch your local television weather broadcast
  • listen to Environment Canada's weatheradio broadcast if you are within range of a transmitter, or
  • look at the weather report for your area on Environment Canada's Internet site at Canadian Weather.
activity pad and pen

Activity 1.1

Ask your students to navigate through the Canadian Weather Web site and find out what the air pressure is for your city or town that day. From the startup page, select your province or territory, and then click on your city or select more cities from the menu on the right.


Tips 1.2

Environment Canada gives air pressure readings in kilopascals. Most barometers, however, measure the air pressure in inches and millibars. To convert kilopascals to millibars, multiply the number in kilopascals by 10. To convert kilopascals to inches divide the number in kilopascals by 3.386.

If all else fails or if you have any mechanical problems with your barometer, such as the black needle does not respond properly to pressure changes, please call your Sky Watcher co-ordinator for help.


Tips 1.3

To convert inches to kilopascals multiply by 3.386 and to convert millibars to kilopascals divide the reading in millibars by 10. For example, a reading of 29.91 inches is 1013.1 millibars or 101.31 kilopascals.

As soon as you have the mean sea level reading in the correct units for your barometer, set the barometer immediately -- the reading will no longer be representative if you wait an hour or two. Turn the barometer over and adjust the small set screw with the markings + and - until the black needle at the front is over the current air pressure. The black needle will move whenever the air pressure changes. Now turn the gold knob on the front of the barometer until the gold needle is over the black needle. The gold needle acts as a reference and will stay put unless you move it. The difference between the two tells you if the air pressure has risen or fallen since you last set it.

Using a nail or screw with a small head, hang the barometer at eye level on a wall indoors, away from direct sunlight, heat or air conditioners. Sunlight and sudden blasts of hot or cold air may affect the readings. Please do not take the barometer off the wall to read it.

To read the barometer, first tap it gently. Wait for a minute or so and take the reading. Convert the reading to kilopascals, if necessary, and record it on your Sky Watchers log sheet. Finally, reset the gold needle by moving it over the black needle.


The thermometer included in the Sky Watchers kit measures not only the current temperature but also the minimum or lowest temperature and the maximum or highest temperature since last reset. This type of thermometer normally relies on either a column of alcohol or a metal coil to react to temperature changes. It isn't necessary to have a maximum/minimum thermometer to participate in the Sky Watchers program, though. If your thermometer measures only current temperature, you may leave the other fields blank when entering your weather observation.


Fast Fact

Because mercury freezes when the temperature drops below -38°C, Environment Canada uses alcohol thermometers and thermisters, which are electronic versions, to record the temperature when it is that cold.

Hang the thermometer at eye level and away from direct sunlight. A shady, secure grassed area on the north side of your school may be the best spot. In setting up your thermometer, try to allow for air to flow across the unit. This will improve the reaction time of the thermometer to changes in air temperature. Those thermometers using a metal coil may be slower to respond to changes than the normal type of liquid-in-glass thermometers. This is due, in part, to the sheer mass of the metal coil, and in part, to the fact that the air flow over the coil is reduced because it's recessed.

If you do not have a secure area for permanent instrument exposure, then store the thermometer in the classroom and hang it up outside about 30 minutes before you take the daily reading. If you do this, though, you will only be able to take a reading for the current temperature. If the thermometer stays outside all the time, then you can record the current temperature as well as the maximum and minimum temperatures.

Some thermometers are calibrated in both Celsius and Fahrenheit degrees. The Celsius scale is the one you will enter on your log sheet for Sky Watchers.

Maximum/minimum thermometers should be reset after each observation.


Tips 1.4

To convert a Fahrenheit temperature to Celsius, subtract 32 from the temperature, then multiply by 5/9. To convert a Celsius temperature to Fahrenheit multiply the temperature by 9/5 and add 32. You may want to ask your students to convert these fractions to decimals as decimals are easier to use in calculations.

activity pad and pen

Activity 1.2

Using the conversion formulas, ask your students to convert the highest and lowest temperatures ever recorded in Canada. Both records were set before the metric system was introduced in Canada. The highest temperature was 107°F at Yellow Grass and Midale in Saskatchewan in 1937. The lowest 0recorded temperature was -81°F at Snag in the Yukon on February 3, 1947. You may want to ask your students to find these communities on maps of the Yukon and Saskatchewan. (The answers, by the way, are 45°C and -63°C respectively)

Sling Psychrometer

This instrument will allow you to determine dew point temperature and relative humidity. The sling psychrometer contains 2 alcohol thermometers. The bulb on the end of one thermometer is covered with cloth, which you will moisten prior to use. This thermometer is called a wet-bulb thermometer. Because heat is required for evaporation, the wet-bulb thermometer will register a decrease in temperature as water evaporates from the cloth. The other thermometer is called a dry-bulb thermometer. Since there is no water and hence no evaporation on this one, the dry-bulb thermometer will show the actual air temperature.

The difference in temperature on the 2 thermometers is an indication of the amount of water vapour in the air. In dry air, the water will evaporate quickly and cause a large drop in the wet-bulb temperature. This makes the difference in readings on the 2 thermometers greater. If the air is moist, little water will evaporate from the wet-bulb and the temperature decrease -- and the resulting difference in readings -- will be small.

Using this instrument, you can check the relative humidity inside your school and outdoors as well when the temperature is 10°C or higher. It is not suitable for use year-round at colder temperatures. At temperatures below freezing, the water on the wet-bulb will freeze and a different technique is required. For this reason, dew point and humidity will not form part of your daily Sky Watchers weather observation throughout the school year. In the fall and spring, though, calculating the relative humidity on a daily basis will give your students a better understanding of the subject.

To use the sling psychrometer, first moisten the cloth on the end of the wet-bulb with water, being sure to saturate it completely. Be careful not to get water on the dry-bulb thermometer. If you do get moisture on the dry-bulb, dry it thoroughly using a piece of paper towel before taking a reading.

Position yourself in an open area, whether indoors or outdoors, an arms-length away from any objects that you might otherwise hit. Grasp the psychrometer by the wooden handle and swing it vigorously in a circular manner for at least 60 revolutions or until the readings stabilize. Quickly record the temperature in degrees Celsius on each of the thermometers, reading the wet-bulb first. The wet-bulb reading will always be equal to or less than the dry-bulb. Subtract the wet-bulb reading from the dry-bulb. This difference is called the wet-bulb depression.

Using the tables provided, find your observed dry-bulb temperature in the column on the left and the wet-bulb depression in the row across the top. Follow across the row and down the column to the intersection of the 2 readings. At the intersection, you will find the dew point temperature and relative humidity corresponding to those readings. Enter these in the space provided on your log sheet.

The concepts of dew point and relative humidity will be discussed at greater length in Chapter 2.

Rain Gauge

You measure the amount of rain which has fallen with the rain gauge. The Sky Watchers gauge has two scales -- one in millimetres and one in inches. As Environment Canada uses the metric system, you record your observations on the Sky Watchers log sheet in millimetres.

To set up the rain gauge, attach it to a post such as a fence post using the metal bracket and screws provided. If there are no posts, sharpen a wooden stake 1 or 1.5 metres high and drive that into the ground. Please be sure the top of the rain gauge sticks above the post and the post is located away from buildings, trees, rain spouts or any other structures which may interfere with the rain falling into the gauge. When mounting the gauge make sure the opening is level -- not tilted -- and the metric side faces outwards. That way, you will be able to read the measurements easily.

To take a reading, look at the level of water in the rain gauge and record the amount in millimetres on your Sky Watchers log sheet. Be sure to empty the gauge and dry it thoroughly with a clean cloth after every reading.

Measuring Snow


Tips 1.5

To convert a measurement in inches to millimetres, multiply by 25.4 and to convert a measurement in millimetres to inches, divide by 25.4

Snow is bulkier than rain and so is measured in centimetres instead of millimetres. The usual way of measuring the depth of snow is with a long ruler or a metre stick. Find a patch of undisturbed snow on flat open ground away from any trees or overhanging roofs. Try to avoid areas where the snow has drifted into piles or the wind has blown the fresh snow away.

Keeping the ruler straight, push it into the snow until the ruler hits the ground below. Measure the depth of snow in centimetres. Do this several times in different spots. Then work out the average depth of snow on the ground by adding your measurements together and dividing by the number of measurements you took.

There are 3 ways to discover how much snow fell since your last observation -- the last time you measured it.

1. Subtract the amount of snow on the ground recorded at the last reading from the amount of snow on the ground recorded today. The difference will be the amount of new snow which has fallen.

Sometimes the reading for the day will be lower than the previous reading. That will happen when the snow has melted, or the weight of the new snow has compacted the snow beneath it, or the measurements were taken at different spots.

2. Use a snow board. You can make this snow board out of a scrap of plywood or arborite which is about 40 centimetres long and 40 centimetres wide. The snow board has to be light enough to sit on top of the snow but heavy enough to stay in place on windy days.

Find a spot in the school yard which is away from trees and overhanging roofs but not an area where snow drifts build up. Push the board into the snow until the top is level with the snow's surface. If the forecast calls for a heavy snowfall, mark the board's location with a flag or stick so you can find it the next day. After measuring the amount of snow on the board, clean it off and place it back in the snow.

3. Find an area in the school yard which you can sweep clean of snow after each measurement. This area, like the one for the snow board, should be away from trees, overhanging roofs and areas where snow drifts pile up. After measuring the amount of snow which has fallen, sweep the area clean.

Sometimes your measurements may not jiv
e with the day's weather. That may happen on those days when stiff winds have blown snow onto your snow board or measuring area. On these occasions, please use the common sense test and ask yourself if it really did snow since the last reading or observation.

Record your measurement of snowfall in centimetres on your Sky Watchers log sheet.

Comparing Rain and Snow

Rain and snow are measured in different units. When you want to compare the two, you work out the water content of the snow. For this, you use the rain gauge and measure the water content in millimetres.

After a snowfall, bring the snow-filled gauge inside and let the snow melt. Then measure the amount of water in the gauge. Generally, 10 centimetres of snow will produce 10 millimetres of water, which is a ratio of 10:1.

There are exceptions. Wet snow falling on a day when the temperature is close to freezing or 0°C, may produce 10 millimetres of water for every 6 centimetres of snow for a snow to water ratio of 6:1. In contrast, the very dry, powdery snow which skiers love may have a snow to water ratio of 30:1. That is 30 centimetres of snow produces 10 millimetres of water.

For the Sky Watchers report, if you have had both rain and snow on the same day, measure the total amount of liquid in the rain gauge in millimetres and enter the figure under Rainfall.

UV Meter

If your school has a UV meter, you will find that activities using the meter are most effective when UV levels are over 3 -- generally from 11 a.m. to 4 p.m. on sunny days in May or June.

A UV meter will measure the burning effect of UV radiation on human skin and express it using the UV Index. Many meters turn on automatically when exposed to sunlight. Consult the instruction manual to determine if your model should be held flat or on an angle. In either case, hold the meter in the palm of your hand, about 30 cm in front of your body and out of the shade. For best results, move away from buildings that might reflect additional light. Make sure your fingers or other objects do not shade the meter, particularly the sensor window on the front edge of the meter. Try not to touch the sensor window as this may scratch or streak the window and affect the readings.

Once the meter is removed from sunlight, it will lapse into standby mode and then shut down entirely to conserve the battery.

To extend the life of the battery in your meter, you may wish to remove it from the meter completely when the unit is stored during school breaks.

Wind Gauge

The wind gauge, which is also called an anemometer, measures the force or speed of the wind. To use the wind gauge stand in an open spot away from any buildings, hills, walls or trees which may block the wind or change its direction and speed.

First unfold the wind gauge's handle. It is on the left hand side of the gauge as you face the dial. Lock the handle in place by sliding the latch on the bottom of the gauge to the left. Find out where the wind is coming from by checking to see which direction tree branches or flags are blowing. Now hold the wind gauge up and into the wind so that the dial is facing you. Watch the speed on the dial. Slowly turn the gauge a little to the left and then to the right watching to see where the wind speed is the greatest. Make a note of that measurement.

This wind gauge measures speed in miles per hour and metres per second. Environment Canada, however, records wind speed in kilometers per hour. You need to convert the reading to kilometres per hour before entering it on the Sky Watchers log sheet.

Winds of less than 10 kilometres per hour do not register well on this wind gauge. On days when the winds are light, you may want to use the Beaufort Scale to estimate the wind speed. British Rear Admiral Sir Francis Beaufort invented this scale in 1805 as a way of estimating the speed of winds at sea. The scale was later modified so that it could be used on land.


Tips 1.6

To convert miles per hour to kilometers per hour multiply the reading by 1.6. A reading of 10 miles per hour is 16 kilometres per hour. To convert metres per second into kilometres per hour multiply the reading by 3.6.

activity pad and pen

Activity 1.3

Ask your students to devise their own wind scale based on what they see around them, while recording wind speed for Sky Watchers -- flags fluttering, leaves blowing around, etc.

Table 1. Beaufort Scale
IfWindsSpeed (km/h)Beaufort
Smoke rises straight upCalmLess than 10
Smoke drifts but weather vanes do not turnLight air1 to 51
Leaves rustle, weather vanes move, you feel a light breezeLight breeze6 to 112
Wind extends a little flag, keeps leaves in and small twigs in motionGentle breeze12 to 193
Wind raises dust, loose paper and small branches kept in motionModerate breeze20 to 284
Wind sways small trees and small waves form on pondsFresh breeze29 to 385
Large branches of trees move, telephone wires whistle and it is
hard to use an umbrella
Strong breeze39 to 496
Trees bend and walking against the wind is hardNear gale50 to 617
Twigs break off treesGale62 to 748
Houses and roofs are damagedStrong gale75 to 889
Trees uprootedStorm89 to 10210
Damage is widespreadViolent storm103 to 11711
Tremendous damage and loss of lifeHurricaneAbove 11712

Wind, Clouds & Weather Phenomena

For the Sky Watchers program you record the direction the wind is coming from as well as the amount of sky covered by clouds. You also describe the day's weather using one of the terms listed under the title Phenomena on the Sky Watchers instruction sheet. Weather phenomena include haze, blowing snow, thick fog, drizzle, rain showers and snow showers.

Wind Direction

The wind direction is the direction the wind is coming from. A north wind, for instance, blows in from the north. There are two ways to find the direction of the wind. You can make a wind streamer using the instructions on page 66, or you can use a compass for reference.

If you decide to use a compass, go outside and with the compass, find north. Then select a landmark such as a hill, building or lake to identify one of the four points on the compass - north, south, east or west. This is your point of reference. To figure out where the wind is blowing from, compare the movement of the flags or tree branches with your point of reference.

If the flags and tree branches are still and you feel no breeze what so ever, then the wind is calm and you record both wind speed and wind direction as "0".

Cloud Cover

The Sky Watchers program uses 4 categories to describe the amount of sky covered by clouds from horizon to horizon.

  • 1. Clear
    • Clouds in the sky
  • 2. A few clouds
    • Less than half the sky is covered with clouds
  • 3. Cloudy
    • More than half the sky is covered with clouds
  • 4. Overcast
    • All the sky is covered with clouds

Types of clouds

There are at least 12 different types of clouds. You may want to identify these too on your Sky Watchers log sheet under Additional Information, even though it is not part of the information you send to Environment Canada. For information on clouds, refer to Chapter 3: Weather Elements - Clouds.

One Last Point

Your students may begin sending in weather reports at any time. They will gain a greater appreciation of the subject if they follow weather trends through the changing seasons.

If your classroom schedule allows it, you should take your observations every school day around 2 p.m. If you take your readings at the same time every day, then you can compare the readings and observations from day to day and week to week. Further, you can compare your readings with those of other schools in the Sky Watchers program because they also take their readings around 2 p.m. You may send your observations to Environment Canada at any time, but if possible please no later than 3 p.m. each day.

To enter your weather observation into our database, visit our Sky Watchers Web site, and follow the links from "Sky Watchers Weather". You will be prompted for your school's observer number and password, so you may wish to record them at the top of each log sheet for reference. If you have any trouble entering your observations, please call your Sky Watchers co-ordinator for help.

Return to Table of Contents

Chapter 2 - What Makes Weather?

Download Chapter 2 (PDF; 1269 KB)

What Makes Weather?

The story of weather starts with the sun. Its energy travels 150 million kilometres to the outer edge of the earth's atmosphere. Some of that energy is reflected back into space by the tops of the clouds and some is scattered by the dust and the water vapour in the atmosphere. About half of the sun's energy reaches the earth. Here it is converted to heat to warm the earth and the air above it as well as melt snow and evaporate water.

All areas of the earth do not receive the same amount of the sun's energy at the same time. There are 3 reasons for this.

First, the earth rotates on its axis every 24 hours creating night and day.

Second, the earth revolves around the sun every year. During the earth's orbit, some regions receive more of the sun's energy than others.

Third, the earth is tilted on its axis at an angle of 23 ½degrees. Without that tilt, the sun would shine directly over the equator all year and there would be no seasons. Instead, the sun's energy hits different parts of the earth at different angles affecting the amount of heat any one part of the earth receives. This unequal heating also sets the air in motion creating global wind belts.

Solar Radiation

Image 1. Solar Radiation: Short-wave radiation partly reflected from cloud top; Short-wave radiation partly transmitted through clouds; Long-wave radiation absorbed and re-radiated by cloud; Short-wave radiation absorbed by ground radiated back as long-wave radiation.


To help your students see the effect of the earth's tilt, try Activity #1.

The Atmosphere

The earth is surrounded by an ocean of air. Meteorologists, the men and women who study weather, refer to this ocean of air as the atmosphere. Scientists have divided it into 4 layers, using temperature and the way it rises or falls with height as one of the criteria.

The 4 Layers of the Atmosphere

Image 2. The 4 Layers of the Atmosphere: Troposhere, Stratosphere, Mesosphere, Thermosphere. The dark line shows how temperatures change with height in the different layers of the atmosphere.

  1. Troposphere is the layer closest to earth. The troposphere is thinner than the other layers. It ranges from 6 to 7 kilometres thick over the north and south poles to 20 kilometres in the tropics. Normally, temperatures in this layer decrease with height to about -50 °C at the outer limits. The troposphere is the layer that produces weather.
  2. Stratosphere is about 11 to 50 kilometres above the earth. Temperatures here increase with height starting at about -50 °C and rising to 0 °C. Ozone gas which absorbs most of the sun's harmful ultraviolet rays is in this layer. Some aircraft fly in the stratosphere.
  3. Mesosphere is 50 to 80 kilometres above the earth. As in the troposphere, temperatures in the mesosphere decrease with height starting at about 0 °C and falling to -80 °C in the outer regions of the layer.
  4. Thermosphere is the layer which is farthest away from the earth's surface. This layer begins at about 80 kilometres above the earth where the temperature is about -80 °C. This increases to about 2 000 °C at the outer edges of the thermosphere.

There are transition zones between the layers of the atmosphere. The transition zone between the troposphere and the stratosphere is called the tropopause; between the stratosphere and mesosphere, the stratopause; and, between the mesosphere and thermosphere, the mesopause.

Global Winds

The earth's tilt of 23 ½ degrees results in the sun's energy striking some areas of the world more directly than other areas. As a result, some parts of the earth such as the tropics are hotter than others. In the warm areas, the air rises as it heats up and is replaced by the colder and heavier air from the north and south poles. In the meantime, the rising warm air fans out towards the north and south poles where it cools, sinks, and moves back towards the equator. And so the cycle continues.

This movement of air from the poles to the equator would take an orderly course if the earth did not rotate on its axis from west to east every 24 hours. But it does and that gives the winds a curve. In the Northern Hemisphere, the rotation of the earth deflects the winds to the right and in the Southern Hemisphere to the left. The effect of the earth's rotation on the winds is called the Coriolis force.

Coriolis Force
Image 3. Coriolis Force: The Coriolis force is named after Gaspard Gustave Coriolis, the French Scientist, who in 1835 described what happens to any object which has been set in motion on a spinning surface. For example, in the Northern Hemisphere, the earth's rotation collects winds to the right.

Over the centuries, the sailors and merchants who plied the oceans exploring or trading named some of these winds. For example, the men sailing the east-west trade routes near the equator called the main east-west winds the trade winds because they were consistent and carried the cargo ships to port on time. Generally speaking, though, the prevailing winds are named after the direction from which they flow. In the Northern Hemisphere, the Polar Easterlies blow from the northeast and the Westerlies blow from the southwest. The Trade Winds in the Northern Hemisphere blow from the northeast towards the equator. Then there are the doldrums, an area of light shifting winds on both sides of the equator. Some people call the doldrums areas of Equatorial Calm.

This pattern repeats itself in the Southern Hemisphere because of the Coriolis force. Here, though, the trade winds flow from the southeast. The Westerlies flow from the northwest and the Easterlies blow from the southeast.

Global pattern of winds
Image 4. Global pattern of winds: Easterly winds dominate weather patterns near the poles and equator, while westerly winds are found in the mid-latitudes.

Fast Fact

Between the trade winds and the Westerlies lies another area of light, variable winds called the Horse Latitudes. This area got its name when sailing ships carrying horses to the West Indies were becalmed here, and ran short of water. The sailors had to throw the animals overboard so they would not die slowly of thirst.

Air Pressure

To understand pressure of any kind, we first need to look at forces. A force is anything that causes a push or a pull; for example, gravity is a force that pulls you against the surface of the earth. This gives you weight. Another example is the floor pushing up against you when you walk on it.

Pressure is the amount of force spread over a surface. If a force is spread over a large area, the pressure it exerts is smaller. If the same force is spread over a smaller area, the resulting pressure is greater.

activity pad and pen

Activity 2.1

Bring in a piece of wood with a single nail driven through it so that the sharp end protrudes out the bottom. A small piece of 2 X 4 is ideal. Ask your students if they would rather have the wood balanced on their foot with the nail pointing up or pointing down. But why? It weighs the same either way! With the sharp end of the nail pointing down, the weight of the wood is applied at a single point giving BIG pressure while with the piece of wood flipped over, the same weight is spread over a larger surface giving less pressure. (For the same reason, if you're in a lineup and the lady ahead of you steps back onto your foot, you'd much rather she were wearing sneakers than spike heels!)

An Italian scientist named Evangelista Torricelli discovered that air has weight in 1644 when he turned a tube full of mercury upside down and put it into a dish of mercury. The mercury in the tube did not rush down and completely spill out into the dish. Torricelli reasoned that the air above the dish of mercury was pushing down on it so the level of mercury in the bowl was unable to rise. From that experiment, he deduced that air pushes down on everything.


To show your students that air indeed has weight, try Activity number 2.

The weight of all the air above you is called air pressure. Air doesn't seem to weigh very much to us because it is a gas. Remember, though, that the atmosphere is many kilometres thick over your head. The average pressure exerted by the air is about 1 kilogram per square centimetre at sea level--or, in kilopascals, 101.325.


Fast Fact

The atmosphere presses down with the weight of 16 tonnes on the body of the average adult.

activity pad and pen

Activity 2.2

Have your students draw a 1 cm by 1 cm square on a piece of paper. How many square centimetres would fit on top of their heads? That adds up to a lot of force. Each 1 centimetre square patch on top of your head feels 1 kg of force. If the radius of your head is 8 cm, you have 200 kg of force pushing down on top of your head alone!

Fortunately, air doesn't just push down on us from above, or we might flatten like a balloon does when you step on it. The atmosphere is composed of a mixture of gases that exert pressure in all directions, pushing equally on all sides of our bodies.

The higher you go in the atmosphere, the lower the air pressure, which makes sense as there is less air above you, pressing down. In the lower levels of the atmosphere close to the earth's surface, the weight of all the air above squeezes the air molecules together, making it denser and heavier. By contrast, in the higher levels, there is less weight above to force the air to compress, and the air molecules can spread out more, making it lighter and less dense.

activity pad and pen

Activity 2.3

To demonstrate that air pushes up as well as down, fill a paper cup or glass right to the brim with water. Now place a piece of cardboard over the top of the cup and hold it in place while you quickly invert the cup. Take your hand away. If atmospheric pressure were not pushing up against the cardboard, the weight of the water would push the cardboard off, causing the water to spill out. Because the air does push up, though, and with a greater force than the water exerts, the cardboard stays in place, appearing to "stick" to the cup.

For example, the air pressure is lower at the top of a mountain than it is at the base. At an altitude of 5 400 metres or 18 000 feet, the air pressure is about half that at sea level. This is the reason you were asked to set your barometer to the mean sea level pressure in Chapter 1. That allows you to compare your readings with those of other schools because all the barometers are using the same reference point - the elevation of zero.

Image showing how air pressure decreases with higher altitudes.
Image 5. Air pressure decreases with altitude


If your students are interested in making a barometer try Activity number 3.

Although you cannot see or hear air pressure, you do feel it, especially when it changes rapidly. For example, if you have ever flown in an aircraft, ridden in the elevator to the top of the CN Tower or taken a chairlift to the top of a ski mountain, there is a good chance your ears popped at some point during the journey. That pop signaled a rapid change in air pressure.


To show your students that air exerts pressure try Activity number 4.

The air pressure also changes when the air heats up or cools down. When heat, a form of energy, is added to a parcel of air, the air molecules move faster and tend to move farther apart from each other. Consequently, when air warms up, it expands and becomes lighter. Conversely, cold air is heavier and denser because the air molecules are less active and closer together. As the atmosphere strives to create a balance, the air moves from areas of high pressure, which are often associated with cool air, to areas of lower pressure, which are often areas of warmer air. This creates wind. The greater the contrast or difference in air pressure between the two areas, the stronger the winds.

Local Winds

The global pattern of winds establishes the prevailing winds over large regions. In Canada, for instance, the prevailing winds are from the west. But local differences in air pressure and air temperature as well as lakes, hills and valleys also affect the direction and strength of the winds.


If your students are interested in making an anemometer and wind streamer, try Activity number 5 and Activity number 6.

The atmosphere behaves like a liquid. If you scoop a cup of water out of a bucket of water, what remains quickly flows in to fill the hole and restore the balance. So it is with air. The atmosphere tries to create a balance by flowing from areas of high pressure to areas of low pressure.

Here, too, the Coriolis force affects the direction of the winds. They blow clockwise around and out of a high pressure area and counter-clockwise into a low pressure area. The greater the difference in air pressure between the two areas, the harder the winds blow. In Canada the wind speed is given in kilometres per hour and the direction is named for the direction from which it blows. For example, a north wind comes from the north.

Wind circulation in the Northern Hemisphere
Image 6. Wind Circulation in the Northern Hemisphere: Winds blow counter-clockwise into an area of low pressure and clockwise around an area of high pressure.


Fast Fact

If you stand with your back to the wind in the Northern Hemisphere, the area of lower pressure will be on your left. Check it out using the diagram of pressure centres and winds.


Fast Fact: If you stand with your back to the wind in the Northern Hemisphere, the area of lower pressure will be on your left. Check it out using the diagram of pressure centres and winds.

Local differences in temperature also help to create local winds, particularly around large lakes such as the Great Lakes. For instance, since land heats up more quickly than water, the difference in temperature between the two creates a breeze. What happens is this. On a warm, sunny day the land near a lake heats the air above which then rises. Cooler air from the lake blows in to replace the rising air, which travels out over the water where it cools and sinks to replace the cooler air blowing on shore. In this cycle, the winds blowing on shore are called Lake Breezes.

In the evening when the sun has gone down, the cycle reverses itself. Since land also cools more quickly than water, the air over the water is now warmer than the air over the land. The air heated by the water rises and is replaced by cool air from the land. At the same time, the warm air from the water moves over the land where it cools and sinks. In this cycle, the winds blowing off shore are called Land Breezes.

A similar process occurs between hills and valleys, where the valleys are normally cooler than the hills during the day. Cities and natural features of the landscape such as forests also affect winds.

Lake Breeze and Land Breeze

Image 7. Lake Breeze: Cooler air over water moving towards land; Air heating over land and rising; Warm air cooling and descending. Land Breeze: Warm air over water rising; Air cooling and descending; Cooler air over land moving towards water.


Fast Fact: In the glossary of Canadian winds a Barber does not cut your hair. A Barber is a strong wind which brings precipitation that freezes on contact, especially if the contact is with hair or beard. A Flaw is not a mistake but another name for a Scud or sudden gust of wind.

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Air Masses

The water and land heat or cool the air above them. This creates large masses of air with roughly the same temperature and moisture content. These air masses extend for hundreds of kilometres and are often classified according to the region that produced them.

For example, air which sits in the Arctic for a few months during the dark days of the polar winter turns cold and dry like the snow and ice below. Meteorologists may call this an Arctic air mass. Similarly, air which sits above the Gulf of Mexico or the Caribbean Sea during the summer months becomes warm and moist. This type of air mass is often called tropical.

Air masses over North America in the summerAir masses over North America in the winter

Image 8. Air masses over North America in the summer.
Image 9. Air masses over North America in the winter.

The weather would be easy to forecast if these air masses stayed put. But they do not. They move, pushed by the circulation of air in the upper reaches of the troposphere. As air masses move, their temperature and moisture content change. For example, an air mass travelling down from the Arctic may warm up as it moves over southern Canada. If the air mass also passes over a large body of water such as Great Slave Lake or Lake Superior, then the air mass may pick up moisture too. Conversely, an air mass may also dry out as it moves inland from the Pacific Ocean. In this case, the air mass may lose its moisture in the form of rain or snow as it rises and crosses over the Coast and Rocky mountains.

There is one other point about air masses, which you have probably noticed. They do not always enter or leave quietly.

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A front is the boundary or transition zone between an air mass, which is entering a region, and the air mass, which is leaving it. Usually the two air masses have originated in quite different places, such as the Arctic and the Caribbean. Consequently, they possess different characteristics of temperature and moisture. The interaction between the two air masses may produce dramatic changes in weather, and sometimes, violent weather itself, such as high winds and thunderstorms.

Meteorologists name fronts after the air mass that is entering the region. If cold air is pushing in from the Arctic, displacing the warm air, then the leading edge of the Arctic air mass is called a cold front. If cold air is retreating, allowing warm air to move in, then the leading edge of the warmer air mass is called a warm front. A warm air mass will never push a cold air mass out of a region because cold air is heavier and denser.

Interestingly, the slope of a cold front is, on average, 4 times steeper than the slope of a warm front. That is because when a cold air mass pushes into an area, there is friction, called surface friction, between the advancing air and the land. This friction causes the leading edge to buckle somewhat. Thunderstorms often develop more quickly along a cold front, because its steeper slope lifts the warm air ahead of it up rapidly, creating ideal conditions for the quick formation of thunderclouds or cumulonimbus clouds.

Cross-sections through warm and cold fronts

Image 10. Cold Front, Warm Front: The slope of a cold front is steeper than that of a warm front because of the friction between the cold air and surface.

activity pad and pen

Activity 2.4: To show your students why a cold front has a steep slope, ask them to rest their hands flat on their desks with their palms down. Then ask your students to slide their hands forward toward the front edge of the desk, pause, and pull them backward to the original position. What happened to your students' fingers as they pushed their hands forward? Was there a difference when they pulled their hands back? The students' fingers probably buckled when they pushed their hands forward, as advancing air does, and then flattened when they were drawn back. This is similar to retreating air.

Weather Maps

One of the tools that forecasters use to identify and locate air masses, pressure systems, and fronts is the weather map. These maps are normally prepared at 3- or 6-hour intervals. Weather observations from hundreds of places in North America are plotted on a weather map like the one on the next page. As there isn't enough room to write out all the observed information and still have the map readable, a code was developed to condense the information into a smaller space. This code is called the station model. The station model uses a graphical format to fit all of the following information into a space about the size of a dime:

  • Temperature and dew point
  • Wind speed and direction
  • Amount of the sky covered
  • Visibility and present weather conditions
  • Types of clouds present
  • Air pressure
  • Change in pressure over the last 3 hours and whether it's rising or falling

Here's how a simple station model looks.

Simple station model

Image 11. Simple Station Model.

Most weather maps are analysed at least in part by computer but forecasters sometimes do the analysis by hand. They begin by sketching in isobars, which are curved lines joining places with the same atmospheric pressure. They look much like the contour lines that show elevation on a topographical map. In Canada, isobars are drawn at 4-millibar (0.4 kPa) intervals. Normally, the forecaster looks for values close to 1000 millibars (mb) and draws that isobar first. For example, if the pressure at one station is 1001.3 millibars and a neighbouring station is 998.7 millibars, then at some point between the 2, the pressure must be 1000. Once the 1000 mb isobar is drawn, the forecaster works up to 1004, 1008, etc., and down to 996, 992, and so on until isobars have been drawn to include all of the pressures on the map.

Once the isobars have been drawn, pressure centres will appear. The forecaster will label them as areas of high pressure (H) or low pressure (L), depending on whether the central pressure is higher or lower than the values around it.

A surface weather map from the Canadian Meteorological Centre

Image 12. A surface weather map from the Canadian Meteorological Centre: A weather map from the Canadian Meteorological Centre showing high and low pressure centres, isobars, station plots, and weather fronts across North America. In this map, high pressure brings fair weather to the Prairies while the North and East are experiencing storms.

The forecaster also marks fronts on the weather map. Sometimes, the transition from one airmass to another is so gradual and takes place over such an extended distance that no clear front is identifiable. However where 2 air masses meet and the temperature and humidity change significantly within a short distance, the forecaster will draw either a cold front or a warm front, depending on which type of airmass is moving in. The forecaster may also choose to shade in areas of cloud and areas of precipitation.

The map is then compared to the previous one to determine how the weather systems have moved and whether they have intensified or weakened. The information gleaned from this map analysis is combined with information from other sources such as radar and satellite imagery to give the forecaster a composite picture of what's happening in the atmosphere.

activity pad and pen

Activity 2.5: Using the weather map provided, have your students study the surface winds near high and low pressure systems. Ask them to describe the difference in pattern of wind circulation around highs and lows. Their findings should reinforce what they learned earlier in this chapter.


Return to Table of Contents

Chapter 3 - Weather Elements

Download Chapter 3 (PDF; 294 KB)


Heat is one form of energy. The sun radiates energy in waves, in this case short waves, to the earth. The atmosphere does not absorb short-wave energy readily. The clouds, dust and water vapour in the atmosphere deflect about half of the sun's energy back into space. What passes through is absorbed by the land and water and converted to heat. The earth radiates this back as long-wave energy, which then warms the air above. In short, the earth acts as a radiator, which you probably know already, if you have ever walked down a long stretch of sidewalk or across a large parking lot on a hot day and watched (or felt) the heat rise from the pavement.

Several factors affect how much of the sun's energy a surface, such as a field, absorbs. One is its colour. This concept is called albedo. The albedo of an object is a decimal fraction that expresses what percentage of the incoming radiation it reflects back to space. Pure white has an albedo of 1.0, which means that all the energy is reflected back. Pure black has an albedo of 0.0, which means that all the energy is absorbed and none is reflected back. This comes into play in the earth's energy equation, too. A field covered by snow has an albedo of about 0.7. The same field covered by crops would have an albedo of 0.2, meaning that it absorbs 80 per cent of the incoming radiation. The more energy a surface absorbs, the more heat it will eventually release back into the atmosphere.


To show your students that the rate at which energy is absorbed depends on the colour of a material, try Activity number 7.

Eventually, all the energy the sun radiates to earth returns to outer space creating the global balance of energy. This prevents the earth from heating up or cooling down. The temperature on your thermometer this morning, however, was probably affected more by the season, the time of day, the latitude, and the geography of your area than by the global balance of energy.


If your students are interested in making a thermometer try Activity number 8.

Night and Day

During the day, the earth receives more energy than it radiates back, so it warms up. At night, however, the earth continues to radiate heat, even though it receives no energy from the sun. Consequently, the earth cools down. This cooling process continues until after sunrise, which is one of the reasons why the lowest temperature for the day is often recorded then.

Winter and Summer

Canadians do not need to be reminded about the effect which the season of the year has on the temperature outside. Canada has its warmest weather when the sun is over the Northern Hemisphere. The sun passes over the equator around March 21 on the way north to the Tropic of Cancer at 23 ½ ° North latitude. This is the sun's northern-most position, which it reaches around June 21. From here, the sun starts the slow slide south again to the equator, reaching there about September 21. During the 6 months the sun is in the Northern Hemisphere, its rays shine down on Canada more directly than they do during the country's winter months, when the sun is over the Southern Hemisphere. For the record, the sun reaches the Tropic of Capricorn at 23 ½ ° South latitude around December 20 when it starts moving north again to the equator.

activity pad and pen

Activity 3.1: With the help of an atlas, have your students locate the spots where these record-setting temperatures were recorded.

Table 3.1 Record-setting temperatures across Canada
Province or TerritoryHighest Temperature (°C)Lowest Temperature (°C)
Alberta43.3 Bassano Dame-61.1 Fort Vermilion
British Columbia44.4 Lytton, Lillooet-58.9 Smith River
Manitoba44.4 St. Albans-52.8 Norway House
New Brunswick39.4 Nepisguit Falls-47.2 Sisson Dam
Newfoundland41.7 Northwest River-51.1 Esker 2
Nunavut33.6 Baker Lake-57.8 Sheppard's Bay
Northwest Territories39.4 Fort Smith-57.2 Fort Smith
Ontario42.2 Atkokan & Fort Frances-58.3 Iroquois Falls
Prince Edward Island36.7 Charlottetown-37.2 Kilmahumaig
Quebec40.0 Ville Marie-54.4 Doucet
Saskatchewan45.0 Midale & Yellow Grass*-56.7 Prince Albert
Yukon36.1 Mayo-63.0 Snag*

* Marks the Canadian record

North and South

The latitude of a region also affects how much of the sun's energy an area receives. The countries around the equator receive more of the sun's direct energy than those that lie farther north or south. That is because the sun's rays are almost, but not quite, perpendicular to the earth's surface at the equator. To reach areas closer to the poles such as Canada, the sun's energy must travel at an angle and pass through more of the atmosphere.  Consequently, by the time the sun's rays reach the country, they are weaker, more spread out and diffuse than the rays that hit the earth around the equator.

The effect of latitude on the sun's rays

Image 13. The Effects of Latitude on the Sun's Rays

Lake, Land, Hill and Dale

Finally, the geography of an area plays a role in its heating and cooling. For example, water warms up and cools down more slowly than land does. That is one of the reasons lake shore communities often have lower temperatures in the summer than communities which are farther inland. Similarly, in the winter, communities on the shores of large bodies of open water often have warmer temperatures than those farther inland. Temperatures also decrease with altitude, which explains why you see snow on mountain tops in July.


Fast Fact: Temperatures drop with height at an average rate of 1.60°C for every 300 metres.

All these factors along with the characteristics of the air mass over your region - is it cold and dry or warm and moist - affect the daily temperature.

activity pad and pen

Activity 3.2: Ask your students to choose another school in the Sky Watchers program and prepare a line graph of the temperatures recorded at your school and at the other school. Find out what schools are using the Sky Watchers program.

Heat Waves

Despite the country's reputation as the land of snow and ice, Canada has heat waves. Environment Canada defines a heat wave as 3 or more consecutive days with temperatures of 32°C or higher. Most heat waves in Canada last about 5 or 6 days.

The worst heat wave on record was in July 1936. The heat rolled into the Prairies from the American southwest in early July and then spread into Ontario. Temperatures climbed to 44.4°C at St. Albans in Manitoba and to 42.2°C at Atikokan and Fort Frances, Ontario. Those records stand today. The heat wave lasted a week and was directly or indirectly responsible for killing 780 people in Canada, about 600 people in Ontario alone.

But the heat is only part of the story of summer. The humidity also plays a role in how hot you feel.


Fast Fact: You can find out what the temperature is by listening to crickets chirp. Crickets chirp faster when it is warm than they do when it is cold. If you count the number of cricket chirps in 8 seconds and then add 4, you will have the current temperature in Celsius degrees. This works 9 times out of 10.


Air is made up of a mixture of invisible gases, primarily nitrogen and oxygen. A small portion of it, however, is water vapour. No matter where you are, the Sahara Desert or the High Arctic, there will be water vapour in the air. The temperature of the air determines the amount of water vapour that can exist in the air. Generally speaking, as the temperature increases, so does the potential for water vapour to exist.

When meteorologists talk about the amount of water in the air, the terms they use most frequently are relative humidity and the dew point temperature.


To show your students 2 ways water enters the air, try Activity number 9.

Relative Humidity

The relative humidity is the amount of water vapour that is actually in the air compared to the amount of water vapour that could exist at that temperature. The figure is given as a percentage. For example, a relative humidity of 100 per cent means the air is saturated and cannot absorb any more water vapour. Similarly, relative humidity of 25 per cent means the air contains only one quarter of the moisture that could be present.

Today, humidity is measured with an electronic hygrometer. Not too many years ago, though, humidity was measured with a mechanical instrument that had a long, naturally blond hair as one of the principal components. As the humidity increased, the hair absorbed moisture and stretched. This caused the indicator arm on the hygrometer to change readings. Blond hair was used because it absorbs moisture more readily than other naturally coloured hair.


Fast Fact: In 1783, the Swiss physicist Horace de Soussure discovered that hair stretches by about 2.5 per cent when the air goes from being completely dry to completely saturated.

You have probably noticed that dry air readily absorbs moisture from surfaces and moist air does not. That is why you may have difficulty cooling off on hot, humid days. Your body cools itself when it is warm by perspiring. The process of evaporation requires heat, and in this case, the heat needed to evaporate perspiration is drawn from your body, effectively cooling it off. On days when the relative humidity is low, perspiration evaporates easily and you cool down. On days when the relative humidity is high, though, perspiration does not evaporate as quickly.


Fast Fact: You have an estimated 2 million sweat glands all working to bring moisture to the surface of your skin where the perspiration evaporates and cools you down. This process may remove 2 litres of water from the average adult an hour. That is why it is important to drink plenty of water on hot days.

Another factor that affects how quickly moisture will evaporate is the wind. For example, on a still calm day, puddles don't evaporate as rapidly as they would on a windy day. That is because, if the air isn't moving, the air immediately above the water puddle will absorb water until it's close to saturation, and then the rate of evaporation slows down. On a windy day, though, the movement of air over the surface of the puddle means that the water surface is continually exposed to fresh drier air and water will continue to evaporate at a faster rate. Similarly, a breeze will cool you off on a hot day by evaporating the perspiration more quickly.

activity pad and pen

Activity 3.3: You can use 2 cookie sheets and a small fan to demonstrate this idea to your students. Set the pans at opposite ends of a table or desk and pour one cup of water into each. Set the fan in the centre and turn it so that the air blows across the surface of only 1 cookie sheet. The water will evaporate from that sheet sooner than from the other.

For the same reason, the directions for using the sling psychrometer in Chapter 1 specified that you should swing the psychrometer vigorously in a circular fashion to increase the air flow over the wet bulb and promote evaporation.

Dew Point Temperature

In contrast to relative humidity, the dew point temperature is the temperature to which the air must cool to be saturated. For example, if the temperature is 23.0°C and the dew point temperature is 10.0°C, then the temperature of the air has to fall to 10.0°C before the air becomes saturated and the water vapour in the air condenses to form water droplets or dew.

That is why dew seldom forms on overcast nights when a blanket of clouds keeps the heat close to the earth. When this happens, the air does not cool down to the point of saturation. Conversely, on clear nights when earth's heat radiates back into space, the air cools down to the dew point temperature and dew forms on objects at the earth's surface such as grass and flowers.

Meteorologists use the term dew point temperature even on the coldest winter day, although frost point temperature may be a better name for it. On cold winter days, the water vapour changes from a gas directly to a solid without becoming a liquid first.

activity pad and pen

Activity 3.4: If you have a loaf of fresh bread to spare for a couple of days, bring it in to school, show it to the students and then put it in the freezer of the school's refrigerator. Leave the bread there overnight so that it freezes and ice crystals are visible inside the plastic wrapping. Show the bread to your students and ask them how and why the ice crystals formed. (The moist air, trapped inside the bag, cooled down to its dew point temperature in the freezer. The water vapour began to condense on the inside of the bag, then froze into ice crystals as the cooling continued.)


The humidex is a Canadian invention which was introduced to the country on June 24, 1965. The humidex is a comfort index. It is a measure of what hot weather feels like to the average person. The air of a given temperature and relative humidity is equated in comfort to air of a higher temperature which has little moisture in it. For example, when the temperature is 320°C and the relative humidity is 75 per cent, the air feels as if it is 460°C. That is the humidex reading. How comfortable people feel in hot, humid weather also depends on their age and state of health.

activity pad and pen

Activity 3.5: If you have a sling psychrometer, use the table provided with it to help your students track temperature, dew point, and relative humidity for at least a 2-week period. This can be done either indoors or outdoors, depending on the season, as long as the O temperature is above 10°C.

Table 3.2 Humidex and your comfort level
30-39Varying degrees of discomfort
40-45Almost everyone is uncomfortable
45-upMany types of work and exercise should be restricted

Fast Fact: The highest humidex ever recorded in a Canadian city was in Windsor, Ontario on June 20, 1953. That day, the humidex  was 52 (Environment Canada's climatologists worked this out using records for temperature and relative humidity.)

Wind Chill

Wind chill is an expression of the cooling sensation you feel on your skin when strong winds are combined with low temperatures. Canada's wind chill index uses temperature-like units to compare the wind's effect to the way your skin would feel on a calm day with that temperature. For example, if the outside temperature is -10°C and the wind chill is -20, your face will feel as cold as it would on a calm day when the temperature is -20°C.

activity pad and pen

Activity 3.6: Position a fan on a cabinet at shoulder-level. Have a volunteer stand in front of the fan and turn it on. The student will feel colder because of the wind's cooling effect, although the temperature in the room has not changed. Now dab some water on one cheek and have the student stand in front of the fan again. The wet skin will feel much colder. This demonstrates how important it is to stay dry when outdoors in winter.

In most parts of Canada, the wind chill index is included in Environment Canada's forecasts when it reaches -25, the point where frostbite becomes a risk. In parts of the country with a milder climate, wind chill warnings are issued at -35. However, wind chill warnings are issued at progressively colder values as you move north. In extreme northern areas, where people are better adapted to very cold conditions, wind chill warnings are issued for values as low as -55.

The wind chill index can help you plan your outdoor activities and decide what to wear. But wind chill is only one of several factors that affect how comfortable you feel on cold winter days. Others include the humidity, your age, your physical condition and how sunny the day is as well as what you plan to do outside.


Fast Fact: The coldest wind chill in Canada occurred at Kugaaruk in the Northwest Territories. The temperature outside was -51°C and the winds were 56 km/h, producing a wind chill of -78.


Water is the only substance that can change from a gas to a liquid to a solid at temperatures that are normally found on earth. What is more, water is everywhere. The air contains water in the form of water vapour, an invisible odourless gas. Clouds form when moist air cools to its dew point - the temperature at which the water vapour condenses - and water droplets or ice crystals form around little particles such as dust, pollution and volcanic ash. Clouds stay up because the water droplets are light and tiny. More than 2 billion of them are needed to fill 1 teaspoon with water.

The air may cool to its dew point and form clouds for several reasons. For instance, cold ground may cool the warm, moist air immediately above it to form low-lying clouds. Clouds may form when a cold air mass lifts up warmer air ahead of it or when air heated by the earth or water rises into the colder reaches of the atmosphere. Clouds also may form when mountains deflect warm, moist air up and over them. In each case, though, the air must continue to cool until it is saturated for the water vapour to condense and form clouds. Clouds form at different levels in the atmosphere, with the stability of the air and the amount of moisture it contains affecting their size, shape, and type.

Air is called stable when it does not rise voluntarily because it is the same temperature as air surrounding it. In fact, stable air has a tendency to stay put unless a range of mountains or a colder air mass forces the air to rise. If this happens and the air is moist, then clouds form, usually in uniform layers.

In contrast, air is called unstable when it continues to rise because it is warmer than the air surrounding it. This parcel of rising air may extend for several kilometres horizontally. It will tend to travel upwards until it reaches the point where it is the same temperature as the air around it. When this happens, meteorologists say the air has reached a balance with the surrounding air.

Image of how Stable Air does not rise voluntarily and how Unstable Air continues to rise on its' own.

Image 14. Stable Air, Instable Air:
Stable Air - Stable air does not rise voluntarily;
Unstable air - unstable air continues to rise on its own.

If air is sufficiently unstable, it may produce clouds which extend high into the atmosphere, some as high as 14 kilometres. These very tall clouds are called cumulonimbus or thunderstorm clouds.

Naming the clouds

In the early years of the nineteenth century an Englishman, Luke Howard classified the clouds according to their appearance and behaviour. Mr. Howard was an apothecary or pharmacist with a keen interest in the atmosphere and all that it contained. He used the scientific language of the day, Latin, to name the types of clouds.

Stratus - Stratus means stretched out or layered.
Cirrus - Cirrus means curl, lock of hair
Cumulus - Cumulus means heap.
Nimbus - Nimbus means rain cloud, cloud burst,
shower and cloud

Oliver Allen. Atmosphere. The Planet Earth Series. Ed. Thomas Lewis. (Alexandria, Virginia: Time-Life Books, 1983) P. 95-96.

From the Ground Up

Low clouds - The bases of low clouds range from near the earth's surface to about 2 kilometres above it. Depending on the season, these clouds may contain water droplets, ice crystals, or a mixture of both.

Stratus clouds - Stratus clouds are the low, uniformly dull, gray clouds which hang heavily in the sky. Their bases may cover the tops of hills or if you live in the city, high buildings. If it is not drizzling already, stratus clouds are a good sign that precipitation in the form of drizzle may be on the way.

Nimbostratus - As the name suggests these are low-lying, dense, gray, clouds which may produce more or less continuous rain, or if is cold enough, snow. These clouds are thicker or deeper than stratus clouds.

Stratocumulus - These clouds have a well-defined rounded appearance and are often organized into rolls with flat bases that have gray or dark gray patches. Stratocumulus clouds are common in the late autumn or in the winter.

Cumulus - These little, puffy, fair-weather clouds commonly form on a summer afternoon. They usually cover less than half the sky and produce no precipitation.

If a cumulus cloud continues to grow because the air is unstable, it will become either a towering cumulus or a cumulonimbus cloud.

Towering cumulus - These begin as cumulus clouds but grow vigorously into rising mounds or towers. Their tops are well-defined and often resemble cauliflowers. The bases are flat and dark. These clouds may produce showers or flurries.

Cumulonimbus - Meteorologists call these clouds CBs. They are thunderstorm clouds, which sometimes produce hail and tornadoes. These clouds can be huge. They are often more than 25 kilometres long and 12 kilometres high with temperatures at their tops as low as -55oC, even in the summer. If you look at this cloud from a distance, it has a well-defined, whitish, anvil-shaped top and a ragged and low bottom. When you look at this cloud from below, it has a dark base with curtains made of heavy rain.

activity pad and pen

Activity 3.7: Ask your students to make a cloud. First, pour 2.5 centimetres of hot water into a jar. Then put a few ice cubes onto a baking dish and place that over the opening of the jar. Now watch what happens as the air inside of the jar rises and is cooled by the ice. (The water vapour in the air condenses into water droplets making a cloud.)

Middle clouds

Clouds with the prefix alto are middle-range clouds. Their bases usually range from 2 to 6 kilometres above the earth's surface.

Altostratus - These are gray or blue-coloured sheets of clouds with little texture. They cover most of the sky. In some spots, altostratus clouds may be thin enough to reveal the sun.

Altocumulus - These are white or sometimes gray clouds with rounded bottoms. The clouds may look as if they are arranged in rolls, rounded masses or thin layers. The individual rolls of cloud appear smaller than those in stratocumulus clouds because altocumulus clouds are farther away. Sometimes you can see the sky or the sun between the rolls but often these clouds cover the whole sky.

Altocumulus lenticularis - These lens-shaped clouds form when a mountain range deflects strong winds upwards on the windward slopes and downward on the leeward slopes. This creates a giant wave or ripple several kilometres in length. Moist air enters the crests of the waves, cools as it rises and forms a cloud. When the air descends, it warms up and condensation stops. Groups of these clouds floating along in what appears to be formation may look like a fleet of flying saucers.

Stages of a Thunderstorm

Image of the 3 stages of a thunderstorm which include Cumulus stage, Towering stage and Cumulonimbus stage.

Image 15. Stages of a Thunderstorm:
1-Cumulus stage,
2-Towering Cumulus,


Fast Fact: Fog and mist are thin layers of stratus cloud that form at ground-level. Like any cloud, fog is composed of millions of tiny droplets of water, or in cold weather, tiny floating ice crystals. The thickness of a fog depends on the concentration of the water droplets. Weather observers report fog if the visibility is less than 1 kilometre, and mist if the visibility is 1 to 10 kilometres.

Image of the formation of altocumulus lenticularis clouds. The clouds form a the top of the wave where the air cools and disappears at the bottom of teh wave where the temperatures are slightly warmer.

Image 16. The Formation of Altocumulus Lenticularis Clouds: The clouds form at the top of the wave where the air cools and disappears at the bottom of the wave where the temperatures are slightly warmer.

High clouds

The bottoms of these clouds generally run from 5 to 12 kilometres above the ground. These clouds are composed mostly of ice crystals.

Cirrus - These thin clouds may appear as wispy streaks or streamers high in the sky. Extensive cirrus clouds may be the first sign of an approaching warm front.

Cirrocumulus - These are thin, white bands of clouds with tufted bottoms. These clouds often look like the ripples in the sand left by waves.

Cirrostratus - This whitish cloud covers the sky in a transparent veil or sheet. The cloud is usually thin enough for the sun to shine through, often producing a halo.

One other point about clouds, they move in the direction that the wind at their altitude is blowing. This is why clouds may travel in one direction while the wind at the surface is blowing in another. That also explains why 2 types of clouds which form at different heights, such as cirrus and cumulus clouds, may blow across the sky at one time but from different directions.

First the Cloud, Then the Rain

Rain, snow, hail, and other forms of precipitation occur when water droplets or ice crystals grow until they are too heavy for the air currents in a cloud to support. This process is slightly different in stable and in unstable air, and produces different types of precipitation.


To show your students how to make a rainbow, turn to Activity number 10.

Stratiform clouds

The clouds that form in stable air are called stratiform clouds. These include stratus and nimbostratus clouds.

A stratus cloud is a shallow layer cloud which can range in depth from 100 metres to 2 kilometres. In these clouds, the air circulates slowly, providing little opportunity for water droplets or ice crystals to collide, combine and grow. Consequently, the precipitation formed in these clouds is small and tends to fall as drizzle or light snow.

A nimbostratus cloud is a deeper cloud than the stratus cloud. A nimbostratus cloud may form when a mountain range or air mass forces a parcel of air to rise. Such a parcel of air may have an area of hundreds of kilometres and may rise slowly, maybe at the rate of 1 to 10 centimetres a second. In these clouds, the air circulates with slightly more vigour than it does in stratus clouds. As nimbostratus clouds may extend upward for 8 to 9 kilometres, there is more opportunity for water droplets or ice crystals to collide and grow. This results in larger droplets than those formed in stratus clouds. Nimbostratus clouds are responsible for most of the steady rain and snow which falls in Canada.


Fast Fact: One million tiny water droplets are needed to form an average rain drop which is about 1 millimetre in diameter. A water droplet needs more than 30 minutes to grow to that size.  The rain clouds must be at least 1 kilometre thick for the growing droplets to remain in the cloud long enough to become raindrops.

Convective clouds

The clouds that form in unstable air are called convective clouds after the convection currents created by the rising warm air and sinking cold air within them. These clouds include towering cumulus and cumulonimbus clouds. Unlike nimbostratus clouds, the updrafts and downdrafts in towering cumulus and cumulonimbus clouds travel tens of metres per second. The force of the updrafts and downdrafts bounces water droplets or ice crystals around many times giving them ample opportunity to collide, combine and grow. The strength of the updrafts and downdrafts also allows the water droplets or ice crystals to grow much larger than they do in a nimbostratus cloud before they become too heavy for the air currents to support them.

The precipitation formed in these clouds usually falls in bursts or showers. Though short-lived, these bursts or showers may drop a lot of rain or snow in a short period of time.

activity pad and pen

Activity 3.8: Ask your students to make a list of all the different sounds, they hear from weather, such as the sound of cars on wet pavement or rain on the roof. Using a tape recorder, ask your students to record a unique sound which they have discovered. When tape is complete, visit other classrooms and have those students guess what it is they hear.


Precipitation comes in three forms, liquid, freezing and frozen - and in Canada, sometimes all in one day. More than 5 trillion tonnes of precipitation fall on this country each year. More than 60 per cent of this precipitation runs off into lakes and rivers. The rest evaporates from the earth's surface or passes back through the plants through the process known as transpiration.


If your students are interested in making a rain gauge, try Activity number 11.

The Pacific Ocean, Gulf of Mexico and Caribbean Sea are the primary sources of water for precipitation in Canada. But water also recycles itself several times between the air and the ground. The water evaporates from soil, lakes, and rivers, rises into the air as water vapour, forms clouds, and then falls elsewhere as rain, drizzle, freezing rain, snow or hail.

Rain, Snow, Drizzle, Ice Pellets, Hail - Canada Has It All

Drizzle - Precipitation is called drizzle when the water droplets are less than 0.5 millimetres in diameter, which is about the size of the head of a pin.


Fast Fact: Drops of drizzle fall at a rate of 1 to 2 metres per second while raindrops reach speeds of 4 to 9 metres per second.

Rain - Precipitation is called rain when the water droplets are greater than 0.5 millimetres in diameter. Some raindrops are as large as 10 millimetres across.


To show your students the different sizes of rain drops, try Activity number 12.

Freezing drizzle and freezing rain - Freezing drizzle and freezing rain occur when there is a shallow layer of air at the earth's surface which is below freezing and a layer of air above it which is warmer and above freezing. Water droplets form in the warmer layer and fall into the colder air. The droplets cool as they fall and freeze when they hit objects such as fences or sidewalks with temperatures which are below zero.

Image of how freezing rain forms. In the winter, there can be as many as 4 different types of precipitation when a warm front passes.

Image 17. How Freezing Rain Forms: In the winter, there can be as many as 4 different types of precipitation when a warm front passes; Rain, Freezing Rain, Ice Pellats, Snow.


Fast Fact: The Ice Storm of 1998 lasted from Jan. 4, 1998 to Jan. 10 1998 and left nearly 3 million people in Ontario and Quebec freezing in the dark.

Ice pellets - Ice pellets form under the same conditions as freezing rain and freezing drizzle. The water droplets form in the higher, warmer layer of air and fall into the lower layer of colder air. In this case, though, the cold layer is deep enough to give the water droplets time to freeze before they hit the ground.

Hail - Hail forms only in cumulonimbus clouds when the strong updrafts carry water droplets high into the upper reaches of the clouds where temperatures are below freezing. Here the water droplets freeze. Layers of ice are added when the updrafts throw more water droplets upward, which then collide with the frozen particles. This process continues until the ice particles become too heavy for the updrafts to support. Then the ice particles fall as hail.


Fast Fact: A hailstone of a few millimetres in diameter needs updrafts of more than 100 kilometres per hour to support it. In Canada, hailstones range in size from 5 millimetres, or the size of a pea to 114 millimetres or the size of a grapefruit.

Snow - Snow is precipitation of white or translucent ice crystals which are clustered together to form snow flakes. The shapes and sizes of snow flakes depend on the temperature and the amount of water vapour in the cloud where the flake forms and in the air through which the flake falls.


Fast Fact: About 36 per cent of Canada's precipitation falls as snow, compared to the world average of 5 per cent.

The big, soggy flakes are conglomerations of hundreds of smaller snow flakes that have fallen through relatively mild air and stuck together. Some of these flakes have measured as much as 2 centimetres across. In contrast, dry snow tends to fall as small, single flakes that do not bind together as they fall through cold, dry air.

activity pad and pen

Activity 3.9: A cubic metre of snow weights about 100 kilograms. Ask your students to measure the size of the sidewalk leading into the school and calculate the weight of the snow which would have to be cleared following a snowfall of 15 centimetres.

Return to Table of Contents

Chapter 4 - Severe Weather in Canada

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Severe weather is a fact of life in Canada. This country has a land area of 9,970,610 square kilometres, making Canada the second largest country in the world after Russia.

Not surprising then that Canada also has a wide variety of severe weather, everything from ice storms to tornadoes. Canadians may joke about the country's weather but severe weather is no joke. Bitter cold and winter storms, for example, kill more than 100 people a year.

This section describes both summer and winter severe weather as well as Environment Canada's severe weather warning program. Severe weather warnings alert people to hazardous weather which may be dangerous to lives or property.

Summer Severe Weather


Thunderstorms are a dramatic, somewhat noisy, but typical part of summer. They develop when warm, moist, unstable air is forced to rise into the atmosphere. This happens for many reasons. For example, some thunderstorms develop along the boundaries or transition zones between warm and cold air masses when the colder, heavier air undercuts the warmer air and forces it to rise. Other thunderstorms pop up when cool lake breezes from large lakes such as the Great Lakes meet hot, humid air farther inland. When this happens, the cooler air undercuts the warmer air and bumps it up into the atmosphere. Still other thunderstorms form when land, which has warmed up over the course of the day, has heated the air above causing it to rise. Storms that form in this manner are called air mass thunderstorms. One variation of air mass thunderstorms is the type that forms early in the day on slopes which face east, such as those on the east side of the Rocky Mountains. The slope of the ground allows the sun's rays to strike the earth at almost right angles, focusing the heat energy on a smaller area. This extra heating kicks off thunderstorms that then drift eastward during the day, carried by the prevailing westerly winds.

In all these instances when the warm air rises, it cools to its dew point temperature and the water vapour in the air condenses to form water droplets. But this does not stop the warm air from rising. It continues to push upward as long as it is warmer than the air around it, stopping only when it reaches air of the same temperature. The rising warm air or updrafts and sinking cooler air, the downdrafts, in developing cumulonimbus clouds bounce the water droplets around so hard they collide with others creating ever larger water droplets. Eventually, these water droplets become too heavy for even the strong updrafts to support and rain falls.

activity pad and pen

Activity 4.1 : The updrafts in a really good thunderstorm may exceed 1,800 metres per minute. Ask you students to calculate what that is in kilometres per hour (Answer: 108 km/h).
They could also work out how long it would take a newly formed water droplet to zip from one third of the way up to the top of a cumulonimbus cloud which is 12 kilometres high (Answer: 4.4 minutes).

Thunderstorm Hazards


At the same time, the turbulence in the cumulonimbus clouds creates positively and negatively electrically-charged areas within the clouds. Scientists do not know why but generally speaking the positive charge develops in the cold upper reaches of a cloud and the negative charge develops in the lower portions of a cloud. This, in turn, induces positive charges in objects on the ground below.


Fast Fact: There is little truth to the saying that lightning never strikes the same place twice. Lightning strikes the CN Tower in Toronto about 70 times a year.

Although air is a notoriously poor conductor of electricity, the electrical charge in the cloud above grows until it overcomes the air's resistance. Interestingly, even though lightning looks like one bolt hurtling towards earth, it is not.

Lightning Safety Tips for Kids

Every thunderstorm produces lightning. Your best defence is to apply the 30-30 rule:

If you can count fewer than 30 seconds between seeing the lightning flash and hearing the thunder, take shelter and remain there until 30 minutes after the last flash of lightning or rumble of thunder.


  • Stay away from windows and doors.
  • Don't use the telephone or take a shower or wash dishes. Don't even touch water faucets, electrical appliances or metal items that would conduct electricity.


  • Unsafe places include open fields, high places, tents, picnic shelters or pavilions, baseball dugouts, indoor (yes, indoor) swimming pools and things that could conduct electricity, like metal fences.
  • If you can't find a safe shelter, make yourself as small a target as possible. Don't lie flat - instead, crouch down with only your toes touching the ground and lower your head.
  • Safety also means no bike riding, skateboarding, or golfing until the storm has passed.
  • If you're swimming or boating, return to shore immediately.
  • In wooded areas, go deep into a stand of trees and find a low-lying area, but never seek shelter under a solitary tree.

In a vehicle:

  • You're safe inside a hard-topped vehicle like a car or RV, because the outer metal body of the vehicle will divert the lightning. But keep your hands in your lap and don't touch anything metal inside the vehicle.

Lightning usually occurs when the electrons holding a negative charge begin moving downward from the cloud to the earth in what is called a step leader. As they get closer to the earth, the negative force of the electrons attracts the positive charge from the earth. This flows upward in what is called a streamer. This streamer or return stroke flows upwards at about 96,000 kilometres a second and at temperatures of 30,000°C, which is six times hotter than the sun. The same process occurs when lightning travels from one cloud to another. In fact, 9 out of 10 lightning strokes flash from cloud to cloud or within the same cloud.


Fast Fact: Lightning kills an average of 7 people and injures 60 to 70 people each year in Canada. Lightning is also responsible for 42 per cent of the country's forest fires. The cost of forest fires caused by lightning has been estimated at $14 billion annually in recent years.

Thunder is a by-product of lightning. Thunder is the sound produced by the sudden and rapid expansion of the narrow channel of air heated by the lightning stroke. You see the lightning, then hear the thunder because the speed of light is about a million times faster than the speed of sound.


Fast Fact: You can work out how many kilometres away a thunderstorm is by counting the number seconds between the time you see the lightning and hear the thunder and dividing that by 3. For example, if you count 15 seconds between the lightning flash and the crack of thunder, then the storm is about 5 kilometres away.

One other point about thunderstorms, they often change as they travel across the countryside. Lakes and the local terrain may affect the strength, movement and duration of storms. For example, if a thunderstorm passes over hills and ridges, it may grow stronger as it climbs up one side and weaker as it goes down the other. A thunderstorm may grow stronger if it moves over a long, stretch of flat land that has been baking in the sun all afternoon or weaker if it passes over a large body of cool water in the late spring.

activity pad and pen

Activity 4.2 : Ask your students to discuss the possible reasons why five times more men than women are struck by lightning. The most likely reason is that more men than women work outdoors.

Only a small percentage of the thunderstorms that rumble across the countryside unleash enough energy to produce severe weather - high winds, heavy downpours, damaging hail or tornadoes.


Hail forms when the updrafts carry water droplets into the colder reaches of a cumulonimbus cloud where they freeze. More layers of ice are added when updrafts hurl other water droplets up and they collide with the now frozen particles. This continues until the ice particles are too heavy for the updrafts to support and the ice particles fall to the ground as hail.

Hail Safety Tips for Kids


  • Follow your lightning safety plan.
  • Stay inside and away from windows that may be struck by hail.
  • Make sure any pets are indoors, too.


  • Find something to protect your body or at least your head.
  • Stay out of ditches or low areas that might suddenly fill with water.

In a vehicle:

  • A car can give you reasonable protection, but be aware that extremely large hail could break windows.

Hail is one of the most destructive forms of severe weather in Canada. Hail stones destroy crops, kill farm animals and cause millions of dollars in damage. Fortunately, though, hail injures only a few Canadians each year.


Fast Fact: The heaviest documented hailstone in Canada fell at Cedoux in Saskatchewan. The hailstone weighed 290 grams and measured 114 millimetres across.


Downbursts are another hazard of large thunderstorms. Downbursts are the downdrafts that usually accompany rain or hail. They plunge to the ground and spread out at speeds of up to 220 km/h - the speed of an EF2 tornado. A microburst is a form of downburst that is less than four kilometres wide and often more intense. Microbursts have caused aircraft to crash and have capsized sailboats.

Straight-line winds or plough winds are other terms used to describe strong downdrafts that can spread out ahead of thunderstorms. Derechos are more damaging and longer-lasting windstorms, often associated with large lines or clusters of thunderstorms. With derechos, winds of at least 90 km/h can be expected to spread damage across an area tens to hundreds of kilometres wide and by definition at least 400 km long.


Fast Fact: People often confuse downbursts with tornadoes, believing that only tornadoes can generate such damaging winds.
Fast Fact: Derechos (pronounced day-RAY-cho) comes from the Spanish word "straight ahead," while tornado comes from the Spanish word for "turn."


Tornadoes occur most often in the hot, humid weather of a late spring or summer afternoon or evening. The thunderstorms that produce tornadoes frequently develop near warm or cold fronts, or other boundaries between warm and cold air masses. Tornadoes are violently rotating columns of air extending from the cloud base to the surface. The lowered air pressure in a tornado often results in the formation of a funnel-shaped cloud. Some tornadoes develop funnel clouds that never quite reach the ground. However, their full extent may be revealed by swirling dust and debris near the ground (or a spray ring at the water surface).

A tornado can range in width from 10 metres to 2 kilometres. For instance, the tornado that ploughed through Edmonton on July 31, 1987, was as much as one kilometre wide. Tornadoes usually travel from the southwest, west or northwest and at the speed of the parent thunderstorm which typically ranges between 20 to 80 kilometres per hour. Tornadoes often travel in a relatively straight line but can change course quickly. On average, most tornadoes last less than 10 minutes and travel less than 10 kilometres. But that is just an average. The Edmonton tornado was long-lived and cut a swath through Alberta's capital nearly 40 kilometres long. The tornado that raced through Grand Valley in southern Ontario, on May 31, 1985, travelled for 110 kilometres before dissipating.

activity pad and pen

Activity 4.3 : To show your students a tornado, try Activity number 13.


The Enhanced Fujita Scale – As of April 1, 2013, Environment Canada will measure the intensity of tornadoes using the Enhanced Fujita scale. This scale is an updated and more accurate version of the original Fujita scale developed by American scientist Tetsuya (Ted) Fujita, a pioneer in tornado research

Table 4.1 The Enhanced Fujita Scale
RankWind DamageWind Speed
EF0Loss of roof covering material on buildings including barns and homes, intermittent trees snapped or uprooted, garden sheds overturned90 - 130 km/h
EF1Partial loss of house roof, barn roof blown off, mobile homes overturned, numerous trees uprooted or snapped, anchored grain bins toppled, garden sheds rolled or carried through the air135 - 175 km/h
EF2Roofs blown off well-built homes, mobile homes and barns destroyed, most trees uprooted or snapped, metal truss electrical transmission towers collapsed180 - 220 km/h
EF3Most exterior walls collapsed in well-built homes, metal buildings and warehouses destroyed, grain bins carried through air, stave concrete silos destroyed225 - 265 km/h
EF4Few walls, if any, left standing in well-built homes, significant damage to exterior walls and some interior walls in low- to mid-rise buildings270 - 310 km/h
EF5Strong frame houses lifted off foundations and carried away, automobile-sized objects fly through the air, large brick or stone churches destroyed, institutional buildings partially destroyed315 km/h or greater

Tornadoes reports have been verified in every province and in two territories. About 62 tornadoes are verified in Canada each year. Most are too weak to cause serious damage. The 1985 Barrie, Ontario and 1987 Edmonton, Alberta tornadoes, however, were rated at F4. And the 2007 Elie, Manitoba tornado was Canada’s first official F5.

Tornado Safety Tips for Kids

Tornadoes most often occur in the afternoon or early evening from May to September, although they have happened at night or even in November. Play it safe if you see a funnel cloud, or if you hear that a tornado warning has been issued for your area.


  • Stay away from windows, doors, and outside walls.
  • In a house, either go to the basement or take shelter in a small ground-floor room near the center of the house, such as a bathroom, hallway, or closet. If that's not possible, shelter under a desk or sturdy table.
  • In an apartment building, don't use the elevator. Move to an inner hallway or room.
  • At school, don't go to the gymnasium. The gym, like arenas and auditoriums, may have a wide-span roof without supports in the middle, making them more likely to collapse if struck by a tornado. In this type of building, move to a smaller room such as bathroom or change room.


  • If you cannot get to a well-constructed building, then seek shelter deep in a stand of trees in a low-lying area, lie down flat and protect your head.
  • If you are in an open area, find a ditch or other low spot, lie down flat and protect your head.
  • In all cases, the key is to get as close to the ground as possible and protect your head from flying debris.

In a vehicle:

  • A vehicle is not a safe refuge when a tornado strikes. Don't get caught in a car, camper, or mobile home.
  • If possible, go to the lowest level of a building with a strong foundation or basement.
  • If no such building is available, then leave your vehicle, find a low-lying area. Lie down flat and protect your head.

Other Rotating Phenomena

Most summer severe weather events, including damaging tornadoes, are spawned by a special type of thunderstorm known as a supercell. With supercells, multiple strong updrafts continue to feed the storm, allowing it to maintain its intensity for several hours. However some tornado look-alikes can form under less developed clouds, over water surfaces, or even under sunny skies.

Dust devils

Normally harmless, dust devils are rotating updrafts or eddies that typically form on hot sunny days when strong surface heating causes the air adjacent to the ground to heat up as well. This localized pocket of hot air rises quickly in a small spinning column, and cooler air rushes in below to replace it. The resulting vortex is made visible by the dust it picks up. Dust devils seldom extend higher than 100 metres, but those that do can flip objects like lawn furniture.

Funnel clouds

As mentioned in the Thunderstorm section, every tornado was once a funnel cloud, but not every funnel cloud becomes a tornado. A spinning condensation funnel can form under large cumulus clouds or weak thunderstorms, but most lack the energy to reach the surface. They spin in mid-air without touching the ground and normally fizzle out soon after they form.


Waterspouts form during periods of cool, unsettled weather from mid-July to late October over large bodies of water like Lake Winnipeg or the Great Lakes . A waterspout looks like a tornado, but is much smaller and weaker. A waterspout is a slender, graceful-looking rotating column of vapour and water extending from the base of a towering cumulus cloud to the water's surface. The diameter of a waterspout ranges from seven to 20 metres and its winds range from 40 to 80 kilometres per hour, which is strong enough to flip a boat. They pose no threat on land as they collapse as soon as they move onshore.

Camping Safety Tips for Kids

Here's one more tip to add to the list. Just as your school has emergency exits to ensure that you have a safe way out of the area, you should pick out a safe refuge near your campsite in case you need to shelter from severe weather.

  • In an organized campground, there may be a comfort station or shower facility nearby.
  • In wilderness camping, look for a low spot in a thick stand of trees.

Identifying your "emergency exit" ahead of time will help you react quickly when summer storms appear.

Tropical Storms And Hurricanes

Tropical cyclone is the name given to any low pressure system which is fueled by the heat released when moist air rises and condenses. A tropical cyclone that intensifies through the three stages described in this section will be called a hurricane if it forms over the Atlantic Ocean or a typhoon if it forms in the Northwest Pacific. The Atlantic hurricane season extends from June to November, with the peak between August and October, when the ocean surface is at its warmest.

But what causes a hurricane to develop? Here are the key ingredients:

  • Hurricanes only form over ocean water that's warm enough to provide a good energy source-it must be at least 26.5°C. Ocean water that warm is only found in the tropics, never off Canada 's shores.
  • The atmosphere above it must cool off rapidly with height, so that rising warm air will continue to rise through the cooler layers, allowing the disturbance to grow.
  • Winds at all levels of the atmosphere from the ocean right up to 9000 meters must be blowing in the same direction and about the same speed. Conflicting wind velocities would hamper the storm's development.
  • A hurricane seldom forms any closer than 500 km to the equator, because the Coriolis Force that makes winds spiral in these storms becomes too weak near the equator.

These ingredients don't always produce a hurricane, but a hurricane will never form without them.

Stages of a Tropical Cyclone

The initial disturbance (called a Tropical Disturbance) is just a large area of thunderstorms that persists for more than one day. If the disturbance becomes organized and the air pressure at its center decreases, strengthening winds begin to spiral and it's classified as a tropical cyclone.

There are three types of tropical cyclones:

  • Tropical Depression: this is the first stage, when the circulation within the system has become organized enough to produce sustained winds of between 37 and 62 km/h. Some Tropical Depressions continue to intensify, while others fizzle out without developing any further.
  • Tropical Storm: If the low pressure centre continues to deepen, with strong thunderstorms and a well-defined circulation pattern that produces sustained winds reaching 63 km/h or more, the system becomes a Tropical Storm and is given a name. Identifying the storm by name reduces confusion when more than one storm is active.
  • Hurricane: If the air pressure at the centre of the Tropical Storm continues to drop, the circulation around it will intensify and wind speeds will increase. When the system produces sustained winds of 119 km/h or more, it is upgraded to hurricane status. At this stage, an "eye" or calm area forms in the innermost part of the storm, with spiral bands of torrential rain rotating around it.

Fast Fact: An alphabetical list of names is prepared well in advance for each hurricane season, using boys' and girls' names alternately. The list contains only 21 names-the letters Q, U, X, Y, and Z aren't used because few names begin with them.

All types of tropical cyclones have the potential to inflict damage, depending on where they strike and the particular hazards associated with that system.

Hurricanes begin to weaken and eventually dissipate when the ingredients that created them-particularly the warm ocean water-are no longer available.

Categories of Hurricanes

Hurricanes are classified by the strength of their winds using the Saffir-Simpson Scale. A Category 1 hurricane has the lowest winds speeds and a Category 5 the highest.

Table 4.2 Saffir-Simpson Hurricane Scale
CategoryWind Speed (km/h)
5> 249

Fast Fact: No Category 3, 4 or 5 hurricane has made landfall in Canada in over a century.

Hurricane Hazards

The hazards commonly associated with hurricanes include high winds, storm surges and flooding from intense rainfalls.


Fast Fact: More than half of the hurricanes that make landfall in the United States produce at least one tornado. This seldom happens in Canada .

In general, most hurricane-related deaths are from storm surges. A storm surge is simply a swelling of water that is driven toward shore by strong winds. This surge of advancing water combines with the normal tide to create an enhanced storm surge that can increase the mean water level by five metres or more, causing serious flooding as it drives onto the shore. In Canada , however, most fatalities result from the flooding rainfalls.

Hurricane Frequency

In an average year, of the dozens of tropical depressions that form, 10 will reach tropical storm status over the Atlantic Basin . The Basin includes the Atlantic Ocean, Caribbean Sea and Gulf of Mexico . Six of them will further develop to become hurricanes and, of these, two or three will be classified as intense hurricanes, reaching Category 3 or higher. Since 1994, these averages have climbed to 15 tropical storms, eight hurricanes and four intense hurricanes.

In an average year, eastern Canada is affected by four tropical cyclones of varying strength. Depending on the storm's path and size, its effects may be felt as far west as Quebec and Ontario or as far north as Nunavut . On the west coast, British Columbia is never affected directly by tropical cyclones. However, in October 1962, the remnants of Typhoon Freda struck the Pacific coast of British Columbia , causing seven deaths and an estimated $10 million in damage. This storm devastated the entire northwestern coast of the U.S. and became known as the infamous "Columbus Day Storm."


Fast Fact: Canada 's best-known hurricane was Hurricane Hazel, which hit southern Ontario in October 1954, resulting in 81 deaths and more than $100 million in damage. Most of the destruction was a result of flooding from in excess of 200 millimetres of rain in less than 24 hours.

The 2005 Hurricane Season was one for the record books. The Atlantic Basin produced 28 named storms, compelling forecasters to use the Greek alphabet to identify storms once the annual list of names was depleted. A record four hurricanes were classified as Category 5 at some point-Emily, Katrina, Rita and Wilma-although none of them came onshore at that strength. Here are a few comparisons.

Table 4.3 Hurricane Season 2005 - Atlantic Basin
 Average2005 Statistics
Number of named storms1028 (new record)
Storms to reach hurricane status615 (new record)
Intense hurricanes2.47 (record is 8, set in 1950)

Hurricane Safety Tips for Kids

  • Follow your family's disaster plan for events such as tornadoes.
  • If you live near the coast, know what the local tides are. High tides will significantly increase the danger from storm surges. Leave low-lying beaches.
  • Go indoors and remain indoors during a hurricane. It's extremely dangerous to travel or move around outdoors during the event.
  • Monitor the storm's progress through Environment Canada's bulletins on Weatheradio, the Internet, or local radio and television stations. A battery-operated radio will ensure your access during power outages.

Winter Severe Weather


The word blizzard was first used to describe a snow storm in the early nineteenth century in the United States. Today, meteorologists use the word to describe one of the worst of the winter's snow storms. Blizzards combine high winds, bitter cold and blowing snow. They are dangerous on several counts. First, the snow is often powdery and fine enough for you to breath into your lungs. Second, the combination of bitter cold and high winds can cause frost bite within seconds. And third, the blowing snow and high winds often reduce visibility to almost zero. Canadian literature abounds with true stories of pioneers, farmers, ranchers and explorers who froze to death only metres away from the shelter they could not see.

In Canada, blizzards are most common in the southern Prairies, the Maritimes and the eastern Arctic. They are relatively rare in Ontario.

Freezing Rain

Freezing rain is a significant winter hazard in Canada , but can also occur in late fall or early spring. Freezing rain glazes trees, hydro lines, roads and sidewalks with ice. Buildups of ice can bring down branches and trees as well as overhead power and telephone lines. This can disrupt power supplies and communications for days. Even a small accumulation of ice may pose a risk to both pedestrians and drivers.

Winter Storm Safety Tips for Kids

Stay indoors and wait out the storm.

  • If you must go outside for a short period, dress in multiple layers of loose-fitting clothing.
  • Outer clothing should be hooded, tightly woven and water repellant.
  • Mittens are warmer than gloves.
  • Wear a hat, because most body heat is lost through the head.
  • If it's very cold, cover your mouth with a scarf to protect your lungs from the cold air.

Never touch a power line that may have come down due to wind or ice buildup. It may still be "live" and you could be electrocuted.

If you become stranded while traveling in a vehicle, wait for rescue:

  • Stay in the car - you won't get lost and the car will provide shelter.
  • Keep dry and warm. If you begin to sweat, remove your hat or one layer of clothing.
  • Keep fresh air in the car by opening the window one centimetre or less on the side away from the wind.
  • Exercise your arms and legs periodically to keep your hands and feet warm.
  • Keep watch for traffic or for search parties.

Ice Storm is a term used to identify particularly severe freezing rain events. The ice storm which hit parts of eastern Ontario , Quebec and New Brunswick from January 4 to 10, 1998, was the worst in recent memory. The storm was directly or indirectly responsible for the deaths of 25 people. At its height, the storm left nearly three million people in Quebec and Ontario without electricity or heat. A week after the storm ended, nearly one million people were still without light or heat.

activity pad and pen

Activity 4.4 : Ask your students to write a story describing what it would be like to live in their homes for seven days in the winter without electricity, running water adn heat from the furnaces. Ask them what supplies they might want to keep on hand to help cope with such an event.

In some respects that storm was typical of most freezing rain storms. For several days a low pressure area over the Texas panhandle pumped warm, moist air from the Gulf of Mexico into southern Ontario and Quebec. This air came in at about the level of low clouds, that is less than two kilometres above the earth's surface.

At the same time, a large and stationary area of high pressure sat over Hudson Bay and pumped cold air into the St. Lawrence and Ottawa river valleys. As warm air is lighter than cold air, the warm, moist air from the south rose above the cold air and stayed there. This is the classic recipe for freezing rain - a layer of warm air hovering above a shallow layer of cold air.

When rain drops began to fall from the clouds in the warm layer of air, they had to fall through the cold layer where temperatures hovered either at the freezing point or just below it. Here, the rain drops cooled to the freezing point or just below it, becoming what meteorologists call super-cooled. Consequently, when these very cold rain drops hit a colder object such as a hydro wire or the branch of a tree with a temperature of below freezing, they froze on contact forming a veneer of ice.

Most ice storms last a few hours. Some continue for up to three days. The ice storm in January of 1998 went on for 6 long days. That was because a high pressure area near Bermuda, which is 1,100 kilometres off the coast of North Carolina, prevented the storms formed in the Gulf of Mexico from heading out to sea in the Atlantic Ocean. Instead the high-pressure area deflected the storms north along the western flank of the Appalachian Mountains in the eastern United States and right into eastern Canada.

Les gouttes de pluie qui se sont mises à tomber des nuages situés dans la couche d'air chaud devaient franchir la couche d'air froid située au-dessous, où les températures se maintenaient tout près, ou juste au-dessous du point de congélation. En passant à travers cette couche, les gouttelettes d'eau refroidissaient sous le point de congélation, devenant ce que les météorologues appellent de l'eau surfondue. En conséquence, lorsque ces gouttes de pluie très froides entraient en contact avec un objet plus froid, un fil électrique ou une branche d'arbre par exemple, elles gelaient aussitôt, formant ainsi un revêtement de glace.

Cold Weather Safety Tips for Kids

Frost-bite and hypothermia (low body temperature) occur when more heat is lost than your body can generate. Although this happens more rapidly on a windy winter day, don't be fooled - you need to guard against frostbite on any cold winter day.

  • Limit your time outdoors when the temperature is extremely cold.
  • Dress appropriately and cover your head, ears and face.
  • Use the "buddy" system. You and a friend can check exposed skin on each other's face for tell-tale white patches where skin is frozen. If you spot frostbite, go indoors immediately for help.
  • Keep active. Physical activity generates more body heat.
  • Stay dry. Wet clothing speeds up the loss of body heat. If your mitts or boots are wet, go indoors to change them.

Severe Weather Bulletins From Environment Canada

Only Environment Canada can issue weather alerts to keep the Canadian public advised of weather events that could affect their safety or property. These weather alerts fall into three categories:

  • Special Weather Statements are issued for events that are not severe enough to merit a warning, but yet might cause general inconvenience or public concern. For example, a Special Weather Statement might be issued to highlight widespread dense fog that could pose a transportation challenge, or to clarify a weather warning that may be in effect near our borders.
  • Weather Watches provide a heads-up that conditions are favourable for severe weather to develop. A Watch might be issued as much as 12 hours in advance, when the potential for dangerous weather has been identified, but the track and strength of the system are still uncertain. Watches may be issued for five different severe weather events to provide more advance notice of the threat. These include a Severe Thunderstorm Watch, a Tornado Watch, a Winter Storm Watch, a Tropical Storm Watch and a Hurricane Watch.
  • Weather Warnings are issued when severe weather is occurring or about to occur. Environment Canada strives for a lead time of six to 18 hours, depending on the type of event. However, thunderstorms often develop rapidly so that lead times on occasion may be less than an hour. The threshold for issuing various types of warnings will depend on the climate of an area as well as local needs.

Winter Weather Warnings

The criteria for winter severe weather warnings differ across the country because the climate itself (or what is considered "normal") also varies from place to place. These are the primary types of warnings issued by Environment Canada in the winter, although the threshold for issuing them may change across the country.

  • A Snowfall Warning is issued when an unusually high amount of snow is expected to fall in a comparatively short period of time. In Vancouver , 5 cm of snow in 12 hours would be unusual whereas in Ontario , a warning is only issued if 15 cm is expected in that length of time.
  • A Blizzard Warning is issued if a combination of strong winds, reduced visibilities in snow or blowing snow and cold temperatures is expected to persist for four hours or more.
  • A Freezing Rain Warning is issued when it is expected to last long enough for the accumulation to create hazardous walking and driving conditions, and possibly damage to trees or overhead wires because of the ice buildup.
  • A Wind Chill Warning is issued when winds of at least 15 km/h are expected to combine with very cold temperatures to produce hazardous outdoor conditions lasting more than three hours. The criteria for this type of warning vary across the country, ranging from -55 in some Arctic regions to -30 in southwestern Ontario .

In some regions, combinations of these phenomena will prompt Environment Canada to issue a broader Winter Storm Warning. Climate differences across the country cause additional types of warnings to be issued in some areas as well. Near large bodies of open water such as the Great Lakes , Snowsquall Warnings are often issued. In some places, blowing snow can reduce visibility enough to warrant a public warning. In main transportation corridors, a sudden drop in temperature from above freezing to below zero can turn a wet roadway into a sheet of ice, and a Flash Freeze Warning may be issued.

Summer Weather Warnings

Although the criteria for summer severe weather warnings may differ from region to region, Environment Canada issues four main types of summer warnings:

  • A Severe Thunderstorm Warning is issued when a severe storm has developed, producing flooding rain, destructive winds with gusts of at least 90 km/h and/or hail at least 10 to 20 mm in diameter.
  • A Tornado Warning is issued when one or more tornadoes or funnel clouds are observed or detected on Doppler radar.
  • A Wind Warning is issued for sustained winds of at least 60 km/h or gusts of at least 90 km/h.
  • A Rainfall Warning is issued when heavy or prolonged rainfall is sufficient to cause local or widespread flooding or flash floods.

Warnings for All Seasons

Some types of weather pose a threat year-round, and Environment Canada will issue appropriate warnings to alert the public of the risk.

Hurricane Warnings

There are also specific warnings that can be issued when hurricanes or tropical storms threaten Canadian territory.

  • A Tropical Storm Warning is issued when an approaching tropical cyclone is expected to produce winds of 63 to 118 km/h within 24 hours.
  • A Hurricane Warning is issued when an approaching tropical cyclone is expected to produce winds greater than 118 km/h within 24 hours.

Keeping Informed

Environment Canada uses a variety of delivery methods to ensure that everyone, no matter what technology is available to them, can access weather information.


Environment Canada has its own radio network, broadcasting continuous weather information 24 hours a day. Known as Weatheradio, this network uses VHF frequencies so that specially equipped receivers will automatically activate when warnings are issued for your area. The network is expanding, so check out the Weatheradio Fact Sheet on the Publications page at What is Weatheradio? to check the transmitter location nearest you.


Millions of people visit Environment Canada's main weather Web site at Canadian Weather to look at radar imagery or to check the forecast for any of the hundreds of towns available on drop-down menus.


The most popular source of weather information for Canadians is still their local media outlet - radio, television, or newspaper - and Environment Canada feeds weather information to them directly through wire services and a special Web site just for media.

activity pad and pen

Activity 4.5 : Listed below are the phenomena for which Environment Canada's meteorologists will issue special weather statements, watches or warnings. Break the list into 2 colums, one showing events that could occur in any part of Canada and the other showing events that are unique to a specific part of the country.

  • Severe Thunderstorm
  • Tornado
    • Twister Sisters
      • Funnel Cloud
      • Cold-Core Funnel
      • Landspout
      • Waterspout
  • Tropical Storm
  • Hurricane
  • Storm Surge
  • High Heat and Humidity
  • Heat Wave
  • Humidex
  • Rainfall
  • Freezing Rain
  • Freezing Drizzle
  • Flash Freeze
  • Wind
  • Les Suêtes
  • Wreckhouse Wind
  • Marine Wind
  • Dust Storm
  • Blizzard
  • Blowing Snow
  • Snowfall
  • Snow Squall
  • Winter Storm
  • Wind Chill
  • Cold Wave
  • Arctic Outflow
  • Frost
  • Weather
  • Fog - Smoke
  • UV
  • Air Quality

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Chapter 5 - Weather and Canadians

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Weather and Canadians

Canadians are fascinated by the weather, and rightly so. Few countries in the world have such a diversity of weather - not only from season to season but also from place to place.

Weather insinuates itself into almost every facet of Canadian life. It affects what you eat, what you wear, how you feel, and even what you do. Weather even provides a built-in excuse for what you do not do . . . because it is too hot or too cold or too wet. Weather has also played the mother of invention to a host of products.

But "Don't knock the weather," as the saying goes, "if it didn't change once in a while, 9 out of 10 people couldn't start a conversation."

activity pad and pen

Activity 5.1: ask your students to collect news reports from television or newspapers about unusual or severe weather for a month. They can report them to the class or put them in a scrapbook or both.


To help your students visualize the range of weather in your area from season to season, have them complete Activity number 14 - graphing exercise.

Weather And Clothes

Weather affects not only the type of clothes you wear but even what colour they are. There is more to the saying, "Never wear white before Victoria Day or after Labour Day" than just concern for style. It is old fashioned sense. Light colours reflect more of the sun's energy than dark colours do and consequently are cooler to wear on a hot sunny summer's day. Conversely, the fashion favourite, black, absorbs much of the sun's energy and keeps you warm on a cool but sunny day. On cold days, you have probably been told to wear several layers of clothing to keep warm. That is because the air trapped between the layers acts as an insulator and slows down the loss of heat from your body.


To show your students the range of weather within your province or territory, have them do some mapping of your region using the blank maps. They could start by locating and labeling the features and communities shown in the table. On a second map, have them plot the temperature that day at each of those communities. This information can be found by visiting Canadian Weather and selecting your province or territory.

Weather and Your Day

Weather affects what you do too, beginning (for some) with the decision of whether to walk or ride to school. If you are bused, the school bus may take longer to get to school on a snowy day; heavier snowfalls may prevent the buses from running entirely. Bitter cold may force you to stay indoors during recess or lunch. A day of steady rain or a sudden but ferocious thunderstorm may prompt a rain check for field days or outings to conservation areas or parks.

Weather also affects what you do in other, more complex ways. Air quality advisories, also called smog alerts, prompt people with respiratory diseases to stay indoors. Many joggers and walkers put off their exercise until the advisory is lifted. Similarly, men and women who work outdoors take additional precautions when winter windchills reach dangerous levels. At the other end of the seasonal spectrum, a high Ultra-Violet Index will induce most people to reach for sunscreen and a hat for protection from the sun's rays.

activity pad and pen

Activity 5.2: Have your students keep a record for one full day of all the decisions made during the day which were based on the weather. For example, did they wear a rain coat, ride a bike, put on a parka, play hockey, go swimming, etc.

Weather and Buildings

Home builders consider the climate of a region when designing the layout of a house. In many parts of Canada, building a house with large windows facing south, for instance, can reduce heating costs. This is because, in winter, the sun is lower on the horizon. The sunshine pouring in through the windows will partially heat the house. Interestingly, in summer, the sun is more directly overhead so it does not have the same effect. The amount of insulation you put in the walls and ceilings of your home may vary, too, depending on winter temperatures in your area.

Contractors must also build in adequate support for the maximum anticipated snow load. The weight of snow on a roof which is under-supported can cause it to collapse.

Although homeowners may rejoice at their savings during dry, mild winters, a bitterly cold winter can cost Canadians as a whole an additional $500 million just to heat their homes.

activity pad and pen

Activity 5.3: Have your students compile a list of the features of their own homes that make good or bad environmental sense - for instance, coniferous trees to provide shade from the sun and shelter from cold winds, double- or triple-pane windows, colour and type of building material.

Weather and Business

Weather has economic consequences for many Canadian industries such as farming, transportation, and construction. Few, if any, occupations are totally safe from the vagaries of weather. For example, even a computer programmer who works from home is dependent on a continuous supply of electricity. The Canadian economy absorbs not only the direct costs for property damage from bad weather but also millions of dollars worth of indirect costs from the loss of revenue from sales and cancelled events. It is not only the large-scale events that affect the economy like the $1 billion Saguenay flood, the multi-million dollar hail storms in Calgary, or the infamous ice storm of '98 in eastern Canada. Even a garden-variety thunderstorm can spell disaster for the farmer who just cut hay or the contractor who just poured $10,000 worth of concrete.

Retailers can almost chart the weather from their record of sales. Fewer air conditioners and ice cream cones are sold during a cool summer than a hot summer, and snow blowers stay on the store's inventory much longer during a winter with little snow. It is not all bad news, though - the same snow-less winter that causes sales of snow blowers to decline is great for the city's snow removal budget.

Many retailers have learned to make the weather work to their advantage. For example, bakeries will produce more hot dog and hamburger buns if fair weather is anticipated for the weekend than they will if storms are predicted, as fewer people will fire up the barbecue.

activity pad and pen

Activity 5.4: Have your students list 10 occupations greatly affected by the weather and identify which weather element is the most critical for each. Then see if they can identify 2 occupations not affected in any way. Remind them that most jobs are dependent to some degree on travel conditions to get to work and the availability of electricity once they arrive.

Weather and Invention

Canada's weather, specifically the winters, has brought out the best in some of the country's more inventive minds. Canadians invented the snow blower, the snowmobile and snow garments such as polar fleece. Not surprisingly Canadians also invented insulation and frozen fish and have perfected the art of making ice wine.

Weather and Geography

Canada is a huge country. It covers 7 per cent of the earth's surface. There are 4,600 kilometres separating the country's northernmost point, Cape Columbia on Ellesmere Island, and the southernmost tip, Point Pelee in Ontario. And there are 4,955 kilometres between Beaver Creek in the Yukon, Canada's westernmost town, and Cape Spear, Newfoundland, which is the easternmost point in North America. It is no surprise, then, that the normal weather patterns are so different from one part of the country to another.


To help your students visualize the climatic variations in Canada, have them do Activity number 15 - mapping exercise.

Climate Change

The terms weather and climate are not interchangeable. Weather is the state of the atmosphere at any given time. Climate is weather taken over a relatively longer period of time. The climate of a region is the longer-term average that describes the type of weather you may expect there from season to season. Or to put it another way, climate is the weather you expect - weather is what you get.

Climate is never static or stable. The earth's natural climate system has always been, and still is, changing. Scientists have looked at information recorded over the ages in ancient rocks, tree rings, and ice sheets. The evidence suggests that the earth has experienced numerous warming and cooling periods over the past 1 million years. Global ice ages appear to have occurred at roughly 100,000 year intervals, followed each time by a dramatic 4° to 6°C warming period. Scientists believe that natural climate change is caused, in part, by periodic variations in the earth's orbit and the sun's output. There is also a close correlation between warm periods and high concentrations of greenhouse gases in the atmosphere.

Greenhouse Gases

Life can exist on earth only because it has an atmosphere. The surface of the earth receives energy from 2 sources: the sun and the atmosphere. Part of the incoming energy from the sun is absorbed by the earth and then radiated back into the atmosphere. Several gases that exist naturally in the atmosphere absorb this energy and, in turn, send some of it back to earth. These are popularly known as greenhouse gases, although the analogy is not strictly accurate. The glass in a greenhouse physically traps the sun's warmth inside whereas these gases do not deflect heat - they absorb it. Greenhouse gases that occur naturally include water vapour, carbon dioxide, methane, and nitrous oxide. Without these gases, the sun's heat would escape and the average temperature of the earth would drop from 15°C to -18°C, too cold to support life.


Fast Fact: The earth receives most of its energy from the atmosphere, rather than directly from the sun. The sun's rays, while more intense, strike only part of the earth at any given time. The atmosphere, on the other hand, covers the whole earth all of the time.

How People Affect The Balance

Human activities seem to be upsetting the delicate balance of greenhouse gases in the atmosphere. They are causing more of these gases to be released into the atmosphere. For instance, carbon dioxide is produced when people drive their cars or burn fossil fuels to heat their homes. The burning of fossil fuels alone adds nearly 22 billion tonnes of carbon dioxide to the atmosphere every year. Plants and trees absorb carbon dioxide but clear-cutting forests reduces the number of trees available to absorb and hold it. Consequently, more carbon dioxide remains in the atmosphere.

Decaying matter in landfill sites and the burning of fossil fuels release large amounts of methane gas. Nitrous oxide is released when chemical fertilizer is used and fossil fuels are burned. Adding more of these energy-absorbing gases to the air means they will radiate even more heat back to earth, adding to the natural warming effect of the atmosphere.


Fast Fact: One car produces 3.5 times its weight in carbon dioxide every year.

Although scientists may not agree on exactly how much global warming will occur, or exactly how much the climate will change, they do agree that some warming has already occurred. Further, they agree that there will likely be more change to come.

Potential Consequences

A rapid warming of the planet could have a huge effect on all forms of life. Melting ice and glaciers could cause the sea level to rise, flooding coastal regions. The climate of various regions could change too quickly for many plants and animals to adjust. Warmer ocean temperatures would affect the fish population, causing some species to disappear and others to migrate. Harsh weather conditions such as heat waves and droughts could also happen more often and be more intense. These are just a few of the many implications of increased global warming.

How to Help

There are many things Canadians can do everyday to reduce greenhouse gas emissions.

  • use the car less - walk, cycle, ride the bus, or start a car pool whenever possible
  • use less energy in the house - turn down the heat when you are away and turn off lights and appliances when you are not using them
  • send less garbage to the landfill - reduce, reuse, recycle, and compost waste whenever possible
  • plant a tree - it will absorb carbon dioxide as well as provide shade to keep your house cooler in the summer and sheltered from the wind in winter.


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Chapter 6 - Ultraviolet Radiation

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Ultraviolet Radiation

Although energy from the sun sustains all life on earth, some forms of the sun's energy can be harmful. Ultraviolet (UV) rays, for example, cause sunburns and skin cancer.

As a result of ozone depletion, much attention has been focused on UV in recent years, but UV rays have always been dangerous. About 76,000 new cases of non-melanoma skin cancers and 4200 melanoma skin cancers are now diagnosed each year in Canada. This is largely a result of poor sun protection practices.


Tips: You may want to cover UV topics in spring as the associated activities work better when UV rays are stronger. Also, learning about UV in April or May would encourage sun protective practices leading up to the time of year when they're needed most.

What is UV?

The sun radiates energy that travels through space like a wave. Some of this energy - about 45 percent of it - reaches us as visible light. The rest is invisible radiation. One form of invisible solar radiation is Ultraviolet or UV. It has a shorter wavelength than visible light but carries more energy. UV is classified into three types, by decreasing wavelength: UV-A, UV-B, and UV-C.

Much of the sun's UV-A reaches the earth's surface. However, most of the UV-B, and all of the UV-C, are filtered out by the earth's atmosphere, primarily by the ozone layer.

Diagram of sun's UV-A, UV-B and UV-C rays and how they are filtered by the ozone layer to reach the earth's surface.

Image 18. The ozone layer absorbs some but not all types of ultraviolet radiation.

Factors Affecting UV

Factors that affect the amount of UV radiation reaching the earth's surface include:

  • height of the sun in the sky, which depends on latitude, time of year and time of day - when the sun is most directly overhead, its rays have the least distance to travel through the atmosphere and the rays are more intense, being focused on a smaller area
  • ozone layer thickness - the thicker it is, the more UV it can absorb
  • altitude - at higher altitudes, there is less atmosphere above to absorb UV rays
  • cloud cover and atmospheric pollution - both can reduce UV levels.

You may want to revisit Activity number 1 to demonstrate how the strength of the sun's rays - including UV rays - varies depending on the angle at which they hit the earth.

The Ozone Connection

The Ozone Layer

Ozone is a noxious, colourless gas with a harsh odour. Fortunately, ozone occurs in greatest concentrations in the stratosphere, forming the ozone layer at an altitude of 15 to 35 km.

The ozone layer is produced naturally, by the reaction of UV rays on ordinary oxygen. Ozone, in turn, will also break apart as it absorbs UV. This cycle of forming, then breaking up ozone molecules maintains a natural balance of ozone in the atmosphere, protecting us from harmful UV radiation. Most ozone is made above the tropics where the sun is strongest, but it is transported around the globe by high level winds.

Ozone Depletion

The natural balance between the production and destruction of ozone has been tipped in the direction of destruction since about 1980 by manufactured chemicals such as chlorofluorocarbons (CFCs). These chemicals have long atmospheric lifetimes, and when they reach the stratosphere, they react with UV to create new ozone-destroying products like chlorine.


Fast Fact: A single chlorine atom can destroy thousands of ozone molecules, and bromine is about 50 times more destructive!

Although much of the earth is affected, thinning of the ozone layer has been most severe over the poles in spring. That means less UV is absorbed by the ozone layer and more reaches the earth's surface.

A Look Ahead

As ozone is made from atmospheric oxygen, the ozone layer can repair itself once the quantity of destructive chemicals in the stratosphere is reduced. However, scientists are concerned that rising levels of greenhouse gases will affect ozone loss, and even with international cooperation, it will likely be at least 2050 before any substantial recovery occurs. Higher than normal UV levels, then, will be with us for decades to come.

UV Effects

Human Health Effects

The thinning of the ozone layer over southern Canada has resulted in an average 5 percent increase in sunburning UV. In the spring, though, UV increases are often much higher. UV can affect human health because it penetrates into the skin and can cause skin cancer. The number of new cases of skin cancer diagnosed each year in Canada has more than tripled over the past 20 years. Since these develop over time, most new cancers have likely been caused by sun exposure which occurred decades ago, prior to any serious ozone thinning. Ozone depletion may worsen the problem unless the effects of increased UV are offset by better sun protection habits.

Sunburn is a short-term, or acute effect of UV radiation. When you get a sunburn, cells in the skin are damaged, resulting in pain. The body responds by increasing blood flow to the small vessels of the skin, causing the redness associated with sunburn. There is a link between repeated, severe (blistering) sunburns and skin cancer later in life.


Fast Fact: More than 1 in 7 Canadians over the course of their lifetimes can expect to develop some form of skin cancer.

In addition to skin cancers and sunburns, over-exposure to UV rays can also lead to other health problems, such as premature aging of the skin, weakening of the immune system and eye problems such as cataracts.

activity pad and pen

Activity 6.1: Ask your students for details of their last sunburn experience, when it happened, when they noticed it, what time they were in the sun that day, and what they were doing. Prepare a log of the results and have your students look for behaviour patterns that contribute to over-exposure.

Other Effects of UV

Plant growth is affected by increased UV levels. Some agricultural crops, such as canola, oats, and even cucumbers, show reduced yields at higher levels of UV. Effects on forests are harder to measure, as trees may be exposed over many decades.

Ultraviolet radiation also has an effect on natural communities. Increased UV exposure in lakes and oceans can damage tiny single-celled plants called phytoplankton, that provide food for fish and other animals. Sudden, brief UV increases during early spring can damage young vegetation or the eggs of fish and frogs which are laid in shallow water.

Increased UV also reduces the lifetime of the construction materials used in our homes and other structures.


Note :
To see the effect of UV on ordinary newspaper, have your students do Activity number 19.

The UV Index

Environment Canada's UV Index program was launched in 1992, the first of its kind in the world.

The UV Index was designed to measure the burning effect of UV radiation on human skin. The simple numerical scale runs from 0 to about 11 in Canada. As you go further south, the Index can go considerably higher, sometimes reaching the teens in places like Florida. The higher the number, the faster you'll burn.

Line Graph of typical clear-sky UV Index Maximum level at bi-monthly intervals throughout the year.

Image 19. Typical Clear-sky UV Index Maximum (Southern Canada): In Southern Canada, the UV index is generally lower in the winter than in the summer. Winter UV Index values range below 1, while summer values range above 7. The curve on the graph shows the typical clear-sky maximum at specific dates during the year.

activity pad and pen

Activity 6.2: If any of your students are going to Florida for March break, you could compare UV readings in the 2 locations. Each day during the week prior to March break, have a student record the UV and amount of cloud at noon. Ask the student going to Florida to do the same while on holiday. Compare the differences and discuss the effect of latitude and sun angle on UV strength.

Environment Canada computers produce a daily UV Index forecast for specific locations, based on the angle of the sun at midday, the predicted amount of ozone overhead and the forecast cloud amount. The UV Index forecast is produced for Canadian cities and for holiday destinations as well. The UV Index forecast is often included in the public weather forecast, especially during the spring and summer. You may see it on your local newspaper's weather page, and may hear it in radio, television or Weatheradio Canada broadcasts. The UV Index forecast can also be found on the Internet.

activity pad and pen

Activity 6.3: To locate the UV Index forecast for Canadian locations, visit Canadian Weather and select Regional Forecast Text from the menu on the left. If your community is not listed in the Daily UV Forecast bulletin, then check your public forecast through the web site instead. The UV Index is included from mid-April to mid-September.

The UV Index forecast represents the maximum value expected during the day. Under clear skies, this will occur at midday when the sun is at its highest point in the sky. In the summer, this generally occurs from 1 to 2 p.m.

Starting in 2004, Canada will follow the Global UV Index guidelines of the World Health Organization. Under these guidelines, there are five categories: Low, Moderate, High, Very High, and Extreme. Learning the significance of each category will help you take appropriate sun protection measures during your outdoor activities.

Table 6.1 UV Index Categories
UV IndexCategory
8 to 10Very High
6 to 7High
3 to 5Moderate
0 to 2Low

Note :
If you're planning a day outdoors with your class, take along a UV meter and do the graphing exercise in the Activities section.

UV Protection

You can still enjoy being outside if you remember to take a few precautions. First, take a moment to find out the weather forecast and the UV Index forecast. If there will be sunshine during your outing, the UV Index forecast will give you some guidance on the appropriate level of sun protection.


Fast Fact: The higher the sun is in the sky, the shorter your shadow, and the stronger the UV. A rule of thumb is that, if your shadow is shorter than you are, then the UV will be 4 or higher and students should protect themselves from too much sun.

When the UV Index is low (0-2).

  • Minimal sun protection required for normal activity
  • Wear sunglasses on bright days. If outside for more than one hour, cover up and use sunscreen
  • Reflection off snow can nearly double UV strength. Wear sunglasses and apply sunscreen

When the UV Index is moderate (3-5).

  • Take precautions - cover up, wear a hat, sunglasses and sunscreen especially if you will be outside for 30 minutes or more
  • Look for shade near midday when the sun is strongest

When the UV Index is high (6-7).

  • Protection required - UV damages the skin and can cause sunburn
  • Reduce time in the sun between 11 a.m. and 4 p.m. and take full precautions - seek shade, cover up, wear a hat, sunglasses and sunscreen

When the UV Index is very high (8-10).

  • Extra precautions required - unprotected skin will be damaged and can burn quickly
  • Avoid the sun between 11 a.m. and 4 p.m. and take full precautions - seek shade, cover up, wear a hat, sunglasses and sunscreen

When the UV Index is extreme (11+).

  • Values of 11 or more are very rare in Canada. However, the UV Index can reach 14 or more in the tropics and southern U.S.
  • Take full precautions. Unprotected skin will be damaged and can burn in minutes. Avoid the sun between 11 a.m. and 4 p.m., cover up, wear a hat, sunglasses and sunscreen
  • White sand and other bright surfaces reflect UV and increase UV exposure

Remember that reflection off snow, white sand, or reflective paint - especially light coloured - can greatly increase the amount of UV reaching the skin and eyes. The unprotected eye is particularly vulnerable to reflected radiation.

activity pad and pen

Activity 6.4: If you have a UV meter, your students can evaluate the protection offered by shade, clothing, and sunglasses by doing the UV experiments that begin on page 69 of the Activities section. Not all fabrics are created equal, nor does all shade offer the same amount of protection.


Fast Fact: Sunbeds and sunlamps generally use UV-A, and are not safe alternatives to natural tanning. A tan, like a sunburn, is a sign that the skin has already been damaged.


Tips: Listen for Environment Canada's UV Indexit's included in your local weather forecast whenever it is forecast to reach 3 (moderate) or more that day.

It is important to adopt good sun protection strategies at an early age, because most skin cancers and other sun-related disorders are preventable.

Here are a few things that can be done at school to reduce exposure to UV:

  • schedule outdoor sports and other activities early in the day to avoid the peak sunshine hours of 11 a.m. to 4 p.m., especially in May and June
  • provide shaded play areas and encourage their use
  • make hats and protective clothing mandatory for outdoor recesses and outside activities
  • encourage the use of sunscreen with a sun protection factor (SPF) of 15 or higher and with both UVA and UVB protection
  • develop a formal school sun safety policy
  • post or announce the daily UV Index forecast

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Chapter 7 - Putting It All Together

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Forecasting Without Computers

There are 3 steps to delivering a forecast - observing, analysing and disseminating. This is where you have the chance to do all three.


For thousands of years, men and women forecast the weather by observing what was happening around them - where the wind was coming from, what clouds were in the sky and whether they were having a bad hair day. Well, perhaps not that. But remember, hair stretches, especially if it is blond, on days when the relative humidity is high and rain may be approaching.

You can develop an eye for weather by using the information you collect from your Sky Watchers weather station and by paying attention to what is happening around you. The sun, moon, clouds, ponds, flowers and even the flies are some of the natural sign posts of the weather which may lie ahead.

First, take a hint from Sky Watchers and be a sky watcher. Observe the skies and, in particular, the clouds, where they move and how they develop.


When you see a bank of wispy cirrus clouds coming in high in the sky on a sunny day, you may expect a change in the weather. Cirrus clouds are sometimes the first sign of an approaching warm front.

Nimbostratus is the dull, gray cloud that covers the sky from horizon to horizon in a blanket of gloom. This cloud usually means rain or drizzle - all day.

On hot, humid days, if towering cumulus clouds pop up rapidly, then showers are likely. There is also a possibility a thunderstorm will develop.

Generally speaking, the more types of clouds there are in the sky, the greater the chance of rain or snow.

On a brighter note, if you see the sun shining behind a thundercloud, you know the cumulonimbus cloud is moving on, and the end of that particular thunderstorm is in sight.

Jet trails

If you look up on a sunny day and see in the cloudless sky a jet leaving a long, white plume, then rain, snow or some other form of precipitation may be on the way. That white plume is called a contrail. It is the condensation trail of ice crystals left behind by the exhaust of a flying jet aircraft. These aircraft fly 8 to 12 kilometres above the ground pulling in very cold, dry air and spewing out hot, water-filled exhaust. The hot water vapour mixes with the colder surrounding air, and in the process, expands and then freezes in 1 or 2 seconds forming a trail of ice crystals.

If a jet leaves no trail or only a short trail or if the trail fades quickly then the air at that level is relatively dry. This means the fair weather is likely to continue. But, if the exhaust trail lingers for an hour or more or spreads across the sky, that means the surrounding air is moist and rain or some other form of precipitation may be on the way.

Sundogs and halos

Halos around the sun during the day or the moon at night are caused by the refraction of the sun's or moon's rays through the ice crystals in cirrostratus clouds. These clouds are an early sign that a warm front is approaching and that rain may be on the way within the next 20 to 24 hours.

Sundogs or mock suns are bright spots on either or both sides of the sun. Their technical name is parhelia. These bright spots can also occur around the moon, in which case they are known as moon dogs. Sun or moon dogs are images of the sun formed as a result of light bending through tiny, floating ice crystals in the air or high clouds such as cirrus or cirrostratus. Like halos, sundogs may mean rain or snow will arrive within 18 to 36 hours.

Be careful though - the most brilliant sundogs occur on cold, clear winter mornings or evenings under high pressure systems, when the air is loaded with ice crystals and the sun is low on the horizon.

Now lower your sights and check out the world around you


Pine cones close and so do some flowers such as tulips and daisies when the relative humidity is high and rain may be on the way. One theory suggests the flowers do this to prevent the pollen necessary for reproduction from washing away.


When dew or frost appear on the ground early in the morning, there is a good chance of a bright day ahead. That is because frost, dew or fog form more readily on clear, cool and calm nights when there are no clouds to interfere with the cooling of the ground. As calm, clear nights are typical of high pressure areas, the fair weather is likely to continue for at least another day.


Flies swarm more readily on humid days because they find flying more difficult in warm moist air. Consequently they sit on the nearest available object.


If you think the pond or ditch smells stronger just before rain, you are probably right. When organic debris such as leaves and grass decay in stagnant ponds, drains or gutters, it produces methane and other gases, all of which have a pungent odour. When the air pressure is high, these gases stay trapped in the mud. But when low pressure systems - which are usually associated with stormy weather - move in, the bubbles of these gases expand, rise to the surface and break loose scenting the air above with the odour of decay.


If the wind changes direction, then the weather may also change. Further, the direction the wind is blowing from may give you a hint at the type of weather in store for your area.

Generally speaking, winds blowing from the southeast, northeast and north are likely to bring steady rain or snow. More pleasant weather may be en route when the winds are blowing from the west to the northwest.

If the wind shifts to the north or northwest from the south or southwest, the temperature may start falling. Again, conversely, if the wind shifts to the south or southwest from the north, then temperatures may rise.

Weather Lore

Weather lore is another source of information about the weather but be careful which weather lore you use. Most weather lore, you may want to file under interesting but fanciful. But some weather lore has firm meteorological foundations. These folk sayings often link one weather sign to the coming weather. They are the product of years of careful observation and probably painful experience. Still, even these do not ring true every time and in every place. For instance, some weather lore does not travel well and what works in one part of the world, such as Europe, does not work in another, such as Canada.

"Cows lie down in a pasture when rain is coming." Perhaps, but cows also lie down when they are tired.

"Red sky at night, sailor's delight. Red sky in the morning sailor's warning."

Yes. You may also have heard this saying with shepherds instead of sailors because sailors, shepherds and farmers needed to know what the next day's weather would be. In any case, this rhyme works well in Canada because the prevailing winds come from the west. High pressure systems which usually bring fair weather are characterized by settling air which traps dust and small particles. When the sun's rays shine through the particles, they colour the sky red. So if the sky is red in the west at night, then the high pressure area and the fair weather usually associated with high pressure systems are coming towards you. If the sky is red in the morning, though, that means the high pressure area and its fair weather have passed you by.

"Showers before seven, fine before eleven."

Yes. Showers in the morning usually do not last long - for good reason. If they formed during the night when it was cool, then when the sun comes up and heats up the day, the humidity drops, the clouds dry out and the rain ends.

"Aches and pains. Coming rain."

It is a well recognized and well researched bit of folk wisdom that changing weather causes existing aches and pains to intensify. One reason is that when the air pressure drops, tissue expands and nerve cells become more sensitive.

"Thunder and lightning turn milk sour." Only if you leave it out of the refrigerator for the whole day (or night).

"Rain long foretold, long last. Short notice soon past."

Yes. This simple verse talks about the scale of weather in time and distance. A large low pressure area with clouds that covers the whole sky and steady rain, often announces its presence with a thin layer of cirrus cloud which moves in about 24 hours beforehand. In contrast, showers or storms from towering cumulus or cumulonimbus clouds often arrive with little warning and leave almost as rapidly.

activity pad and pen

Activity 7.1: Ask your students to interview their grandparents or senior citizens in your community about weather lore or folk sayings. Then ask your students to select and test two or three sayings. Do they work?


Now, you are ready to forecast the day's weather, using everything at your disposal -- the readings from the instruments in your Sky Watchers weather station, your observations of the sky and the world around you as well as your knowledge of weather lore. Here are a few guidelines to help you.

Look for cloudy, unsettled weather when:

  • the barometer falls;
  • the wind blows strongly in the early morning;
  • the temperature at night is higher than usual;
  • the clouds move in different directions at different levels;
  • high, thin, wispy cirrus clouds increase, sometimes producing a ring around the sun or moon;
  • the clouds darken on a summer afternoon;
  • the sunrise is red.

Expect steady rain or snow when there have been signs of unsettled weather and:

  • the wind is south or southeast;
  • the pressure is falling; (A hint: If the pressure falls slowly, rain or snow will come within a day; if it falls rapidly, expect rain soon.)
  • the clouds are low and uniformly flat and gray;
  • there is a ring around the moon or sun;
  • leaves show their undersides.

Look for showers and, perhaps, thunderstorms when:

  • the barometer falls;
  • dark, threatening thunderclouds accompany a west wind;
  • thick, towering cumulus clouds develop rapidly in the spring or summer during early afternoon;
    winds blow from the south or southeast;
  • you hear loud static on your AM radio. (thunderstorms are an hour away)

Look for clearing skies when:

  • the barometer rises;
  • the wind shifts into the west or northwest;
  • the temperature falls rapidly, especially in the afternoon;
  • the dark clouds become lighter and rise steadily in altitude;
  • the humidity decreases.

Look for continued pleasant weather when:

  • the barometer is steady or rising slowly;
  • the wind continues to blow from the west or northwest;
  • the number of clouds decreases in the afternoon;
  • the clouds are higher in the sky;
  • the evening sky is clear and the setting sun looks like a ball of fire;
  • the morning fog breaks within 2 hours of sunrise;
  • there is heavy dew or frost on the ground in the early morning;
  • the moon shines brightly and the wind at night is light.

Look for heavy snow when:

  • the temperature is between -10°C and -1°C;
  • the barometer falls rapidly;
  • the winds blow from the east or northeast;
  • a storm lies to the south and east of you.

Look for temperatures to rise when:

  • the winds shift from the north or west to the south;
  • the night sky is overcast and there is a moderate wind from the south;
  • the sky is clear all day;
  • in the winter, the barometer falls.

Look for temperatures to fall when:

  • in the winter, the barometer rises steadily;
  • the wind shifts from the south to the north or northwest;
  • the wind is light and the sky is clear at night;
  • the skies are clearing - this is especially true in the winter;
  • snow flurries fall with a west or north wind.

Look for fog when:

  • warm winds are blowing humid air across a large body of much colder water or a large stretch of cold land;
  • the night before the sky is clear, the winds are light and the air is humid;
  • warm rain is falling ahead of warm air;
  • the temperature of the water is warm and the air is much colder.

One last suggestion to help you when you forecast the weather. This comes from Blame it on the Weather, by David Phillips, a senior climatologist at Environment Canada, "One indicator makes lucky your guess, two indicators make errors much less; so take the weather sign at its word if you look again and see a third."


activity pad and pen

Activity 7.2: Ask your students to form forecast teams. Using the information they have collected from their Sky Watchers weather station, their observations of the sky and the world around them and the weatherlore they have collected, ask the teams to put together a weather forecast for the next day. Then ask the teams to suggest how they plan to tell others about their forecasts. They could, for example, do a weather forecast each afternoon before they go home, broadcast it over the school's public announcement system or post the forecast on the bulletin board in the classroom or the school hall. Next, ask the teams what clothes and outdoor activities are suitable for the weather they have forecast for the next day. Finally, your students may want to keep a record of their forecasts and of the weather which actually occurred.

If your students had fun with this activity, they could be tomorrow's forecasters. Environment Canada has a continuing requirement for meteorologists, atmospheric scientists, hydrological technicians, and electronic technicians, to name just a few of the career opportunities. To keep these career choices open, students need only maintain math and science courses as they progress through school. For more information, contact your Sky Watchers co-ordinator.

Forecast Activity

Today's Weather: _______________________________________________________________ 

Date and time of Weather Observation: ______________________________________________

Cloud type and cloud cover: _______________________________________________________

Weather: _______________________________________________________________________

Air pressure:  ____________ rising falling

Wind speed and direction: __________________________________________________________

Preciptiation : (type and amount in millimetres) _________________________________________

Temperature : ____________________________________________________________________

Tomorrow's Weather Forecast: ______________________________________________________

Sky condition (ie. sunny, overcast, etc.) _______________________________________________

Weather: ________________________________________________________________________

Wind speed and dirction: ___________________________________________________________

Precipitation: (type and amount) _____________________________________________________

Afternoon temperature : ____________________________________________________________

Based on my forecast, I recommend the following activities:


A short walk not too far from shelter
A trip to the local museum, library or art gallery by bus
A long hike
A long car trip to visit relatives
Outdoor sports such as baseball, swimming, skiing, snow boarding
Indoor activities such as playing board games or reading a book
Cycling in the park or through open space
Cleaning up the school yard

Forecasting With Computers

Environment Canada's meteorologists follow the same 3 steps which Sky Watchers do when preparing and delivering a forecast - observing, analysing and disseminating.


Meteorologists use the same type of information collected by Sky Watchers. The staff at Environment Canada, however, rely increasingly on sophisticated new remote-sensing technologies which pull in data from orbiting satellites, weather radars, lightning detectors, and weather balloons.


The United States launched the first weather satellite - called TIROS - in 1960. Soon after, in 1963, Canada opened a laboratory in Toronto to process satellite pictures. Today, each of Environment Canada's weather centres has its own satellite receiver to pick up photos transmitted from space.

Weather satellites have become an indispensable tool for observing and forecasting weather. Previously, forecasters could not see entire weather systems. With the photographs sent from the satellites, though, they are able to observe cloud formations over large areas of the globe, even areas where weather observing stations are sparse - such as in the Arctic or over the oceans.

In the past, forecasters laboriously collected weather reports, drew up weather maps, and identified weather systems. By repeating this procedure every 6 to 12 hours, they estimated the speed and direction of movement of each system. Today, forecasters can string together successive satellite pictures and then animate them. From the animated loop, they get precise information on the motion of and changes to weather systems over a set time period. In addition to weather forecasting, meteorologists and other scientists use satellite pictures to determine snow cover, monitor ice conditions, and detect forest fires.

Environment Canada uses images from 2 types of weather satellites: the geostationary satellite and the polar orbit satellite.

A geostationary satellite orbits around the earth's equator at an altitude of about 36,000 kilometres. This satellite completes one orbit every 24 hours, which is the same length of time it takes for the earth to rotate on its axis. The result is that the satellite remains over the same spot on the earth's surface.

Each geostationary satellite, then, monitors the same portion of the earth continuously, producing a picture every 15 minutes. Because its position relative to the earth stays the same, forecasters are able to put together and animate consecutive pictures from the same satellite to show a movie of the weather. This is the view normally seen on the evening news.

A polar orbit satellite travels at a much lower altitude, about 860 kilometres above the earth and provides more detailed images. As the name suggests, when this satellite circles the earth, its orbit carries it over the North and South Poles. The polar orbiter circles the earth about 14 times each day. However, as the earth rotates under it, each successive orbit covers a swath about 2 time zones further west. For example, the satellite's 10:00 a.m. pass may take it north to south over the province of Ontario. By the time it goes all the way down over the South Pole and back up the other side of the earth, the earth has rotated enough that the satellite's next sweep may be over Saskatchewan.

These weather satellites produce 2 main types of images. The first type requires visible light (light you can see) just like 35 millimetre cameras. These visual shots are the easiest to interpret, as they are comparable to what you would see with your own eyes if you were on the satellite. However this type of image is only transmitted during the daylight hours and cannot be used overnight. The second type of image is infrared. The equipment senses temperatures and displays them in shades of grey - the colder the temperature of the ground or cloud top, the whiter it appears on the image. Conversely, the warmer a surface, the darker it appears. This type of picture allows forecasters to monitor clouds overnight as well.

Weather radar


The word radar is an acronym for radio detection and ranging. This technology was developed prior to the Second World War as a way of detecting and locating hostile aircraft. Sometime later, meteorologists began to use it as a means of detecting and locating precipitation in clouds.

Weather radar uses microwave energy to measure the size, motion, and concentration of water droplets or ice crystals within a storm. This energy is transmitted in a burst. Then the antenna on the radar listens to see how much is bounced back by the precipitation. That is why, when precipitation is detected, it is called an echo. The greater the size or density of water droplets, the more microwave energy is scattered back to the antenna.

Conventional radars are used to determine the severity of storms and their motion. Their range is limited to 200 to 400 kilometres.

Doppler radars

In addition to measuring the intensity of precipitation, Dopplar radar measures the speed and direction of the motion of precipitation within storms. This helps forecasters to identify the tell-tale circular rotation typical of budding funnel clouds. Further, this radar can detect areas of high winds in the atmosphere not observable from the ground. It can also sense areas of wind-shear. These are regions where the wind's direction and/or its speed changes dramatically within a relatively narrow layer of the atmosphere. Meteorologists believe this to be an indicator of severe weather including the development of tornadoes.

Doppler radars are named after the Austrian physicist J.C. Doppler. He hypothesized that the frequency of the sound waves from a moving source would increase as they approached an observer and decrease as it moved away. You have probably observed it - or more accurately, heard it - sometime in the past week when a train passed by blowing its whistle or when a car or truck passed by with its horn blaring.

The whistle's pitch climbs as the train comes towards you and then drops noticeably as it speeds away. This happens because as the train approaches you, its motion combines with the motion of the sound wave from the whistle and compresses it. When the train continues off into the distance, the pitch of the sound drops because the sound wave you hear is no longer being compressed by the motion. This process is called a frequency shift and is known as the Doppler effect.

Doppler weather radar is not the only place where the Doppler effect is put to good use. Radar guns are also based on the Doppler effect. Baseball officials use these radar guns to measure the speed of a baseball when it leaves the pitcher's hand. The police use them to detect speeders.

Environment Canada has a Doppler weather radar network.  Doppler weather radars are located across Canada,  from Vancouver Island in British Columbia to Holyrood, near St. John's, Newfoundland.

These new radars will have a range of 250 kilometres. The full network covers those areas of the country which are prone to severe weather. About 90 per cent of the country's population lives in these areas.

Lightning detectors

Canada has a network of 81 lightning detection units across the country. The sensors on these units can accurately place lightning strikes to within 500 metres of where the lightning hits, and are capable of detecting more than 90 per cent of the lightning strokes.

The data from the sensors are relayed to a satellite and then to Environment Canada's weather centres. Lightning detectors relay information about lightning strikes, including their location and whether they were cloud-to-cloud or cloud-to-ground lightning. Meteorologists use this information to help track the motion and intensity of thunderstorms. On a day when large thunderstorms develop, the lightning detection system can record upwards of 15,000 lightning strikes per hour over an area the size of southern Ontario.

Canada's lightning detection network is integrated with the system in the United States creating the first North American lightning detection system. This allows Canadian and American meteorologists to exchange data on weather and work more closely together.

Weather Observations

At the surface:

Staffed and automatic weather stations transmit weather data at least once an hour from all over the continent. They send information on everything from air pressure to visibility, giving forecasters an hourly snapshot of surface weather patterns.

To compare weather reports from different parts of the country or different parts of the world, though, it is essential to establish that the observations were taken at the same time. But local time varies even from one end of Canada to the other. Because of the earth's rotation, the sun rises first in eastern parts of the country - when it's 8 a.m. in Halifax, it is only 4 a.m. in Vancouver. To clearly identify the time the observations are taken, all countries label their weather observations in Universal Time, formerly called Greenwich Mean Time.


Fast Fact: Greenwich Mean Time got its name by virtue of the fact that the prime meridian (0o longitude) runs through Greenwich, England.

activity pad and pen

Activity 7.3: Have your students convert the present time to Universal Time. To help them do this, have them record the local time in hours and minutes. Convert this to the 24-hour clock by adding 12 hours if it is past noon. Then apply the correction for Universal Time from the chart below. (If you are on Daylight Savings Time right now, the offset will be 1 hour less.)

Table 7.1 Time Zones of Canada
Time Zone
Offset for Standard Time
Newfoundland+ 3 ½ hours
Atlantic+ 4 hours
Eastern+ 5 hours
Central+ 6 hours
Mountain+ 7 hours
Pacific+ 8 hours

Environment Canada uses several different types of automatic weather stations to supplement reports from human observers. Most automatic stations transmit their observations by telephone line. In remote locations, however these stations can be set up to use solar-charged batteries as a power source and relay their observations by communications satellites.

Environment Canada's newest type of automatic weather station uses the very latest in remote-sensing technology. For example, the height of a cloud is measured by transmitting a laser beam up into the sky and timing the reflection of that light by the bases of the cloud. The precipitation sensor is basically a Doppler radar that measures the speed at which precipitation particles are falling. This, combined with the air temperature, identifies the type of precipitation. That is because droplets of different size and composition fall at different rates. To measure depth of snow, a high-frequency pulse of sound is transmitted toward the ground and the length of time required for it to travel to the ground and back tells meteorologists how far it is to the snow's surface. Some stations are even equipped with video cameras so that forecasters can dial in to see a digital picture of the weather at that location.

In the upper atmosphere:

Because weather is a process involving the entire atmosphere, Environment Canada also releases weather balloons twice a day from selected sites. These balloons carry instruments and transmitters as high as 30 kilometres into the atmosphere. As the balloons rise, the equipment sends back information about the temperature, air pressure, relative humidity, and winds at various levels in the atmosphere. When the balloons finally expand enough to burst, the small, white disposable instrument boxes float back to earth on parachutes.

Further, Environment Canada relies heavily on volunteer weather observers who collect information. For example, in the climate network, volunteers record daily temperatures and precipitation from weather stations in their own backyards. CANWARN volunteers are ham radio operators who have been trained in severe weather reporting. They watch the skies when severe weather is expected and alert Environment Canada if they witness severe weather such as hail or funnel clouds.

Finally, because weather really is a global affair, meteorologists use observations gathered by weather services all over the world.


Regardless of the technology used to collect the data, all the information plays a role in preparing the daily weather forecast. To produce a forecast for a particular town or region, the meteorologists need to know what the present weather is at that location and what is happening hundreds of miles up stream of the community. In addition, meteorologists must also consider how the weather system approaching the community is likely to change as it advances.

For example, they look at satellite and radar images to track the movement and development of storms. The rate of change in air pressure at observing stations tells meteorologists where and how quickly the high and low air pressure systems are moving. Information about the direction and speed of the wind at the mid-point of the atmosphere - 5.5 kilometres above the earth's surface - shows meteorologists what currents are steering the weather. Although the prevailing movement of weather across Canada is from west to east, weather systems can move up from the south, push down from the north, or back in from the east.

Today, computers are an essential tool for producing forecasts. Meteorologists use computers to store, display, analyse, and manipulate data from all of these sources. The supercomputer in Environment Canada's Montreal office is the largest in Canada. The computer has been programmed with the laws of physics that govern the behaviour of the atmosphere. That computer ingests information from all sources, analyses it, and projects the movement and development of weather systems in a series of 12-hour snapshots. These theoretical projections of how weather systems may evolve provide guidance for meteorologists as they prepare the forecasts.


Once the forecast is written, the next and equally important step is to tell people what it is. Today, meteorologists use a mix of the many technologies available to get the forecasts out to the pubic. They are sent to television and radio stations and newspapers, posted on the Internet, included on telephone recordings, and broadcast over Environment Canada's Weatheradio network.

activity pad and pen

Activity 7.4: Now that your students have finished the program and have become weather-wise, let them have some fun with their new knowledge. Suggestions for designing their own board game can be found in chapter 8.

Return to Table of Contents


PDF Version (PDF; 675 KB)

Activity Number 1 - An Experiment
Purpose - To see the effect of the earth's tilt

Activity Number 2 - An Experiment
Purpose - To show that air has weight

Activity Number 3 - Building A Weather Instrument
Purpose - This project explains how to make a barometer to show changes in air pressure

Activity Number 4 - An Experiment
Purpose - To show that air exerts pressure

Activity Number 5 - Building A Weather Instrument
Purpose - An anemometer measures the speed of the wind. You can make one easily with a ping pong ball and the protractor from your math set

Activity Number 6 - Building A Weather Instrument
Purpose - To make a wind streamer for use as a wind vane to discover from which direction the wind is blowing

Activity Number 7 - An Experiment
Purpose - To show that the rate at which the sun's energy is absorbed is affected by the colour of a material

Activity Number 8 - Building A Weather Instrument
Following the instructions, your students can build their own thermometer. They can then compare its performance against the Sky Watchers thermometer.

Activity Number 9 - An Experiment
Purpose - To show that water vapour enters the air through evaporation and transpiration

Activity Number 10 - An Experiment
Purpose - To make your own rainbow

Activity Number 11 - Building A Weather Instrument
This is a simple rain gauge that students can make on their own

Activity Number 12 - An Experiment
Purpose - To observe and compare different sizes of raindrops

Activity Number 13 - An Experiment
Purpose - To observe a tornado

Activity Number 14 - Graphing
Goal: To plot a graph

Activity Number 15 - Mapping
Goal: to locate and name major geographic features, bodies of water and communities in your region

Activity Number 16 - Mapping
Goal: To locate the capital of Canada, the 10 provinces and 3 territories and their capital cities on a map and label the 3 oceans, the Great Lakes, and Hudson and James Bays

Activity Number 17 - Mapping
Goal: To show how the climate varies across a country with the size and geography of Canada

Activity Number 18 - Design A Board Game

Activity Number 19 - An Experiment
To demonstrate the effect of UV on newspaper

Activity Number 20 - Today's UV
Purpose - To increase understanding of daily variation in UV

Activity Number 21 - Made In The Shade
Purpose - To show the importance of reducing direct UV exposure, and to illustrate the degree of protection provided by various sources of shade

Activity Number 22 - UV And Clothing
Purpose - To demonstrate the effectiveness of a variety of fabrics on reducing UV

Activity Number 23 - UV And Sunglasses
Purpose - To show that some sunglasses block a high percentage of UV radiation

Supplement Activity Number 1 - A Demonstration
Purpose - To illustrate the difference between visible and invisible air pollution.

Supplement Activity Number 2 - A Graphing Exercise
Purpose - To allow students to measure the ground-level ozone in their area, and to examine the trend over a specific length of time.

Supplement Activity Number 2 - A Graphing Exercise (Optional)
Purpose - To allow students to measure the ground-level ozone in their area, and to examine the trend over a specific length of time.

Supplement Activity Number 3 - The Clean Air Game
Purpose - To familiarize students with air pollution vocabulary and concepts

Supplement Activity Number 4 - Breathing Troubles
Purpose - To simulate the breathing troubles of children with asthma and other breathing problems

Supplement Activity Number 5 - The Rubber Band Test
Purpose - To demonstrate the effect air pollution can have on rubber

Supplement Activity Number 6 - Smog Prediction
Purpose - To allow students to apply what they have learned to predicting smog levels in their area.

Return to Table of Contents

References and Resource Materials

PDF Version (PDF; 97 KB)

Prepared by:
Environment Canada Library Downsview - Ontario Region
Revised July 18, 2001


  • Allen, Oliver E. Atmosphere. The Planet Earth series. Alexandria, Virginia: Time-Life Books, 1983.
  • Dickinson, Terence. Exploring the sky by day: the Equinox guide to weather and the atmosphere. Camden East, ON : Camden House, 1989.
  • Engelbert, Phillis. The Complete Weather Resource. 3 vols. Detroit: U.X.L., 1997. Vol.3. Forecasting and Climate.
  • Environment Canada. A Matter of Degrees: A Primer on Climate Change. Ottawa: Environment Canada, 1997
  • Environment Canada. Ice Storm '98: January 4-10, 1998. Ottawa: Environment Canada, 1998.
  • Environment Canada. Learning Weather Kit. 2 vols. Ottawa: Environment Canada. Vol 1. Knowing Weather: Facts and Myths.
  • Environment Canada. Sky Watchers Guide: Pacific and Yukon Region. Vancouver: Environment Canada.
  • Environment Canada. Weather Watchers Teachers' Guide. Edmonton: Environment Canada, 1997.
  • Environment Canada. Wind, Weather & Waves: A Guide to Marine Weather in the Great Lakes region. Ottawa: Environment Canada, 1998.
  • Environment Canada, Atlantic Region. East Coast Marine, Weather Manual: A guide to local forecasts and conditions. Ottawa: Minister of Supply and Services, 1989.
  • Ludlum, David, M. The Audubon Society Field Guide to North American Weather. New York: Alfred A Knopf, 1991.
  • Phillips, David. The Climates of Canada. Ottawa: Ministry of Supply and Services, 1990
  • Phillips, David. The Day Niagara Falls Ran Dry. Toronto: Key Porter Books Ltd., 1993.
  • Phillips, David. Blame it on the Weather: Canadian Strange Weather Facts. Toronto: Key Porter Books Ltd., 1998.
  • Pommainville, Pierre. Aware: Aviation Weather Already for Emergency. 2nd ed. St. Hubert: Environment Canada, Quebec Region. 1996.
  • Schonland, Sir Basil. The Flights of Thunderbolts. 2nd ed. Oxford: Claredon Press, 1964.
  • Williams, Jack. The Weather Book: An Easy to Understand Guide to the USA's Weather. New York: Vintage Books, 1992.
  • Wood, Richard, A., ed. The Weather Almanac. Detroit: Gale Research, 1996.
  • Wyma Brenda. Weather. Cypress, California: Creative Teaching Press, 1995.
  • Wyatt, Valerie. Weather Watch. Toronto: Kids Can Press Ltd., 1990.

Web Sites Used for the Sky Watchers Guide to Weather

Primary Grades K-3

  • Ardley, Neil. La météo. Texte français établi par Kidi Etonde Bebey.
    Paris : Bordas Jeunesse, 1993. (Le petit chercheur)

    ISBN 2-04-019695-1 (2-4)
  • Ardley, Neil. The science book of weather.
    Toronto : Doubleday Canada, 1992.
    ISBN 0-385-25386-9 (2-4)
  • Bower, Miranda. Experiment with weather. Science consultant, Bob Aran ; Education consultant, Ruth Bessant.
    Ocala, FL : Action Publishing, 1992. (Jump science book)
    ISBN 1-882210-96-2 (2-4)
  • Brandt, Keith. What makes it rain: the story of a raindrop. Illus. By Yoshi Miyake.
    Mahwah, NJ : Troll Communications, 1996.
    ISBN 0-89375-583-4 (K-3)
  • Branley, Franklyn M. Down comes the rain. Illus. by James Graham Hale.
    New York : HarperCollins Publishers, 1997.
    (Let's-read-and-find-out science books)
    ISBN 0-06-025338-X (K-3)
  • Branley, Franklyn M. Flash, crash, rumble and roll.
    New York : Harper Collins, 1985. (Let's-read-and-find-out science books)
    ISBN 0-690-04425-9 (K-3)
  • Branley, Franklyn M. Hurricane watch.
    New York : Harper Collins, 1985. (Let's-read-and-find-out science books)
    ISBN 0-690-04471-2 (K-3)
  • Branley, Franklyn M. It's raining cats and dogs : all kinds of weather and why we have it.
    Boston : Houghton Mifflin, 1987.
    ISBN 0-395-33070-X (K-2)
  • Branley, Franklyn M. Rain & hail. Rev. ed.
    New York : Thomas Y. Crowell, 1983. (Let's-read-and-find-out science books)
    ISBN 0-690-04353-8 (K-3)
  • Branley, Franklyn M. Snow is falling. Rev. ed. Illus. by Holly Keller.
    New York : Harper Collins, 1986. (Let's-read-and-find-out science books)
    ISBN 0-06-445058-9 (K-2)
  • Branley, Franklyn M. Tornado alert.
    New York : Harper Collins, 1988. (Let's-read-and-find-out science books)
    ISBN 0-690-04688-X (K-3)
  • Burby, Lisa N. Heat waves and droughts. 1st ed.
    New York : PowerKids Press, 1999.
    ISBN 0-8239-5292-4 (2-4)
  • Butler, Daphne et Denis-Paul Mawet. Pourquoi le vent souffle-t-il? Montréal : Les Éditions École Active, 1994.
    ISBN 2-89069-440-2 (K-3)
  • Butler, Daphne. What happens when wind blows?
    Austin, TX : Raintree Steck-Vaughn, 1996.
    ISBN 0-817241531 (K-3)
  • Cole, Joanna. The magic school bus inside a hurricane.
    New York : Scholastic Inc., 1995.
    ISBN 0-590-44686-X (K-3)
  • Cooper, Kay. Too many rabbits and other fingerplays : about animals, nature, weather and the universe.
    New York ; Toronto : Scholastic, 1995.
    ISBN 0-590-45564-8 (K-1)
  • Craig, Jean M. Questions and answers about weather.
    New York : Scholastic Inc., 1996.
    ISBN 0-59041142-X (K-3)
  • De Paola, Tomie. Clouds. Words and pictures by Tomie de Paola.
    New York : Holiday House, 1975.
    ISBN 0-8234-0259-2 (hc)
    ISBN 0-8234-0531-1 (pbk) (K-3)
  • DeWitt, Lynda. What will the weather be? Illus. by Carolyn Croll. New York : HarperCollins, 1991. (Let's-read-and-find-out science books)
    ISBN 0-06-021596-8 or
    ISBN 0-06-445113-5 (pbk) (K-3)
  • Evans, David and Claudette Williams. Seasons and weather.
    New York : Scholastic, Inc., 1993. (Let's explore science series)
    ISBN 0-590-74592-1 (K-3)
  • Gakken Co. Ltd. Staff. Wind and weather.
    New York : Time-Life, 1989. (A Child's first library of learning series)
    ISBN 0-8094-4829-7 (K-3)
  • Gibbons, Gail. Weather forecasting.
    New York : Four Winds Press, 1987.
    ISBN 0-02-737250-2 (K-3)
  • Gibbons, Gail. Weather words and what they mean.
    New York : Holiday House, 1990.
    ISBN 0-8234-0805-1 (K-3)
  • Gillis, Jennifer Storey. Puddle jumpers : fun weather projects for kids. Illustrations by Patti Delmonte.
    Pownal, Vt. : Storey Communications, 1996.
    ISBN 0-88266-938-9 (pbk) (2-4)
  • Hewitt, Sally. Weather.
    New York : Children's Press, 2000. (It's science!)
    ISBN 0-516-21657-0 (1-3)
  • Hiscock, Bruce. The big storm.
    New York : Atheneum, 1993.
    ISBN 0-689-31770-0 (2-4)
  • Hiscock, Bruce. When will it snow?
    New York : Atheneum, 1995.
    ISBN 0-689-31937-1 (2-4)
  • Hopkins, Lee Bennett. Weather. Poems selected by Lee Bennett Hopkins.
    New York : HarperCollins, 1994. (An I can read book)
    ISBN 0-06-021463-5 (K-2)
  • Humphrey, Paul. Weather. Illus. by roger Stewart and Shirley Tourret.
    London ; New York : Children's Press, 1997. (Step-by-step geography)
    ISBN 0-516-20238-3 (K-3)
  • Kalman, Bobbie and Janine Schaub. The air I breathe.
    New York : Crabtree Pub. Co., 1993. (Primary ecology)
    ISBN 0-86505-556-4 (K-3)
  • Krupp, Edwin C. The rainbow and you. Illus. by Robin Rector Krupp.
    New York : HarperCollins Publishers, 2000.
    ISBN 0-688-15601-0 (2-4)
  • Llewellyn, Claire. Why do we have wind and rain?
    London : Hamlyn, 1995.
    ISBN 0-60058522 (K-3)
  • Mayes, Susan. What makes it rain?
    London : Usborne Pub., 1989.
    ISBN 1-851233237 (K-3)
  • The magic school bus kicks up a storm[videorecording]. (Based on the Magic school bus series by Joanna Cole and illustrated by Bruce Degen).
    [New York, N.Y.] : KidVision, 1999. (Scholastic's the magic school bus)
    1 videocassette (ca. 30 min).
    ISBN 1-568-32838-9 (K-3)
  • The magic school bus kicks up a storm : a book about weather. (From an episode of the animated TV series produced by Scholastic Productions, Inc. ; based on the Magic school bus books written by Joanna Cole and illustrated by Bruce Degen)
    New York : Scholastic, Inc., 2000.
    ISBN 0-439-10275-8 (K-3)
  • Malam, John. Wacky weather. Illus. by Mike Foster. Toronto : Macmillan Canada, 1998, 1997. (How it works)
    ISBN 0-7715-7565-3 (2-4)
  • Martin, Terry. Pourquoi il y a des éclairs? : et autres questions sur la météo. Richmond Hill, Ont. : Éditions Scholastic, 1997.
    ISBN 0-590-16684-0 (K-3)
  • Martin, Terry. Why does lightning strike? : questions children ask about the weather.
    Richmond Hill, Ont. : Scholastic Canada, 1996.
    ISBN 0-590-24945-2 (K-3)
  • Owen, Andy. Rain. Andy Owen and Miranda Ashwell. Des Plaines, ILL : Heinemann Library, 1999. ((What is weather?)
    ISBN 1-57572-789-7 (K-3)
  • Owen, Andy. Watching the weather. Andy Owen and Miranda Ashwell.
    Des Plaines, Ill. : Heinemann Library, 1999. (What is weather?)
    ISBN 1-57572-792-7 (K-3)
  • Petty, Kate. People chase twisters. Illustrators, Peter Roberts and Jo Moore.
    Brookfield, Conn. : Copper Beech Books, 1998. (I didn't know that .)
    ISBN 0-7613-0715-X (lib. bdg.) or
    ISBN 0-7613-0647-1 (trade) (2-4)
  • Richardson, Joy. The weather.
    New York : Franklin Watts, 1992. (Picture science)
    ISBN 0-531-14164-0 (1-3)
  • Rowe, Julian and Molly Perham. Weather watch!
    Chicago : Children's Press, 1994. (First science)
    ISBN 0-516-48142-8 (1-4)
  • Simon, Seymour. Lightning.
    New York : Morrow, 1997.
    ISBN 0-688-14639-2 (hc) 0-688-16706-3 (pbk) (K-3)
  • Simon, Seymour. Storms.
    New York : Morrow, 1989.
    ISBN 0-688-07413-8 (hc) 0-688-11708-2 (pbk) (K-3)
  • Simon, Seymour. Tornadoes.
    New York : Morrow, 1999.
    ISBN 0-688-14646-5 (hc) 0-688-14647-3 (pbk) (2-4)
  • Simon, Seymour. Weather.
    New York : Morrow, 1993.
    ISBN 0-688-10547-5 (1-4)
  • Singer, Marilyn. On the same day in March : a tour of the world's weather. 1st ed.
    Illus. by Frané Lessac. [New York] : HarperCollins Publishers, 2000.
    ISBN 0-06-028187-1 (K-2)
  • Spier, Peter. Crash! Boom! Bang!
    Garden City, N.Y. : Doubleday, 1990.
    ISBN 0-385-26569-7 (K-2)
  • Wallace, Karen. Whatever the weather.
    Bolton, Ont. : Fenn Publishing Ltd., 1999. (Know it all readers. Level 1)
    (ISBN 1-55168-215-X (PreS-1)
  • Weather and climate [videorecording].
    [Mahwah, N.J.] : Troll Associates, 1977, 1986. 1 videocassette (ca. 25 min.). (K-3)

Junior Grades 4-6

  • Archer, Cheryl. Snow watch.
    Toronto : Kids Can Press, 1994.
    ISBN 1-55074-190-X (4-6)
  • Armbruster, Ann, and Elizabeth A. Taylor. Tornadoes.
    New York : Watts, 1993. (First books)
    ISBN 0-531-15666-4 (4-6)
  • Arnold, Caroline. El Niño : stormy weather for people and wildlife.
    New York : Clarion Books, 1998.
    ISBN 0-395-77602-3 (5-7)
  • Artell, Mike. Weather whys : questions, facts and riddles about weather.
    Glenview, IL : GoodYearBooks, 1995.
    ISBN 0-673-36173-X (4-6)
  • Asimov, Isaac. What's happening to the ozone layer?
    Milwaukee : Gareth Stevens Publishing, 1992.
    ISBN 0-8368-0795-2 (4-5)
  • Beecroft, Simon. The new book of El Niño.
    Brookfield, Conn. : Copper Beech Books, 1999.
    ISBN 0-7613-0920-9 (lib. bdg.) or
    ISBN 0-7613-0797-4 (pbk.) (4-6)
  • Bender, Lionel. Heat and drought.
    Austin, Tex. : Raintree Steck-Vaughn, 1998. (Living with the weather)
    ISBN 0-8172-5051-4 (4-6)
  • Bianchi, John. Snow : learning for the fun of it.
    Newburgh, Ont. : Bungalo Books, 1992.
    ISBN 0-92185-09-4 (4-6)
  • Breen, Mark. The kids' book of weather forecasting : build a weather station, "read" the sky & make predictions. With meteorologist Mark Breen and Kathleen Friestad. Charlotte, VT : Williamson Publishing, 2000. (A Williamson kids can! Book)
    ISBN 1-885593-39-2 (4-6)
  • Buxton, John. Weather. [illustrated by John Buxton; written by Tom Kierein]
    Washington, DC : National Geographic Society, 1994.
    ISBN 0-7922-2782-4 (4-6)
  • Carroll, Colleen. The weather : sun, wind, snow, rain.
    1st ed. New York : Abbeville Kids, 1996. (How artists see)
    ISBN 0-7892-0031-7 or
    ISBN 0-7892-0478-9 (library ed.) (4-7)
  • Casey, Denise. Weather everywhere.
    New York : Macmillan, 1995.
    ISBN 0-02-717777-7 (4-6)
  • Christian, Spencer. Can it really rain frogs? the world's strangest weather events.
    New York : Wiley, 1997.
    ISBN 0-471-15290-0 (4-6)
  • Dickinson, Terence. Exploring the sky by day : the equinox guide to weather and the atmosphere.
    Camden East, ON : Camden House, 1989.
    ISBN 0-920656-73-0 (4-6)
    Buffalo, N.Y. : Firefly Books, 1997. (Reprint)
    ISBN 0-920656-71-4 (pbk) (4-6)
  • Elsom, Derek. Weather : an accessible guide that really explains the elements.
    London : Marshall Publishing, 1997. (Your world explained)
    ISBN 1-84028-158-8 (4-6)
  • Encyclopedia Britannica Educational Corporation. The atmosphere in motion. [videorecording] Rev. ed.
    Chicago, IL : Encyclopedia Britannica Educational Corporation, 1987.
    1 videocassette [14 min.]
    ISBN 0-83473-654-3 (5-8)
  • Farndon, John. Weather : how to watch and understand the weather and its changes.
    Toronto : Stoddart Pub. Co., 1992. (Eyewitness explorers)
    ISBN 0-7737-2581-4 New York : DK Publishing, 1992 ISBN 1-56458-019-9 (4-6)
  • Fergusson, Angus. The UV Index, weather & you : the UV Index Children's Sun Awareness Program : activity information guide.
    Downsview, ON : Science Assessment and Integration Branch, Meteorological Service of Canada, 2000.
    ISBN 0-662-28949-8 Govt. Cat. No. EN56-154/2000E (5-8)
  • Fergusson, Angus. L'indice UV, le temps & vous : Programme de l'indice UV pour la sensibilisation des enfants aux effets du soleil : guide d'activités d'information.
    Downsview, ON : Direction de l'évaluation et de l'intégration scientifique, Service météorologique du Canada, 2000.
    ISBN 0-662-84694-X Govt. Cat. No. EN56-154/2000F (5-8)
  • Flint, David. Météorologie et climat.
    Saint-Lambert, Québec : Héritage
    , 1994.
    ISBN 2-713016150 (4-6)
  • Flint, David. Weather and climate.
    London ; Toronto : Gloucester Press, 1991. (Hands on science)
    ISBN 0-531-17321-6 (4-6)
  • Ganeri, Anita. Weather.
    New York : Franklin Watts, 1993. (Nature detective)
    ISBN 0-531-14250-7 (4-6)
  • Harper, Suzanne. Clouds : from mare's tails to thunderheads.
    New York : Franklin Watts, 1997. (First books)
    ISBN 0-531-20291-7 (4-6)
  • Harper, Suzanne. Lightning.
    New York : Franklin Watts, 1997. (First books)
    ISBN 0-531-20290-9 (4-6)
  • Jennings, Terry. Weather.
    Jersey City, N.Y. : Park West Publications, 1999.
    ISBN 0-563-37382-2 (3-5)
  • Jones, Lorraine.
    Super science projects about weather and natural forces. New York: Rosen Publishing Group,2000. (Psyched for science)
    ISBN 0-8239-3105-6 (3-5)
  • Kahl, Jonathan D.W. Hazy skies : weather and the environment.
    Minneapolis, MN : Lerner, 1997. (How's the weather)
    ISBN 0-8225-2530-5 (5-8)
  • Kahl, Jonathan D.W. Storm warning! : the power of tornadoes and hurricanes.
    Minneapolis, MN : Lerner, 1993. (How's the weather)
    ISBN 0-8225-2527-5 (5-7)
  • Kahl, Jonathan D.W. Thunderbolt : learning about lightning.
    Minneapolis, MN : Lerner, 1993. (How's the weather)
    ISBN 0-8225-2528-3 (5-7)
  • Kahl, Jonathan D.W. Weather watch : forecasting the weather.
    Minneapolis, MN : Lerner, 1996. (How's the weather)
    ISBN 0-8225-2529-1 (5-7)
  • Kahl, Jonathan D.W. Weatherwise : learning about the weather.
    Minneapolis, MN : Lerner, 1992. (How's the weather)
    ISBN 0-8225-2525-9 (5-7)
  • Kahl, Jonathan D.W. Wet weather : rain showers and snowfall.
    Minneapolis, MN : Lerner, 1992. (How's the weather)
    ISBN 0-8225-2526-7 (5-7)
  • Kerrod, Robin. The weather.
    New York : Marshall Cavendish, 1994. (Let's investigate science)
    ISBN 1-85435-630-5 (4-6)
  • Kramer, Stephen. Avalanche.
    Minneapolis : Carolrhoda Books, 1992.
    ISBN 0-87614-422-9 (4-6)
  • Kramer, Stephen. Eye of the storm : chasing tornadoes with Warren Faidley.
    New York : Putnam Pub. Group, 1999. ISBN 0-399-23029-2 (hc) (2-5)
    ISBN 0-698-11766-2 (pbk) (2-5)
  • Kramer, Stephen. Lightning.
    Minneapolis, MN : Carolrhoda Books, 1992.
    ISBN 0-87614-659-0 (4-6)
  • Kramer, Stephen. Tornado.
    Minneapolis, MN : Carolrhoda Books, 1992.
    ISBN 0-87614-660-4 (4-6)
  • Kramer, Stephen. Tornado : nature in action.
    Minneapolis, MN : Carolrhoda Books, 1997.
    ISBN 1-57505-058-7 (4-6)
  • Lee, Sally. Hurricanes.
    New York : Franklin Watts, 1993. (First books)
    ISBN 0-531-15665-6) (4-6)
  • Lye, Keith. Temperate climates.
    Austin, Tex. : Raintree Steck-Vaughn, 1997.
    ISBN 0-81724-827-7 (4-6)
  • Jones, Lorraine.
    Super science projects about weather and natural forces. New York: Rosen Publishing Group,2000. (Psyched for science)
    ISBN 0-8239-3105-6 (3-5)
  • Kahl, Jonathan D.W. Hazy skies : weather and the environment.
    Minneapolis, MN : Lerner, 1997. (How's the weather)
    ISBN 0-8225-2530-5 (5-8)
  • Kahl, Jonathan D.W. Storm warning! : the power of tornadoes and hurricanes.
    Minneapolis, MN : Lerner, 1993. (How's the weather)
    ISBN 0-8225-2527-5 (5-7)
  • Kahl, Jonathan D.W. Thunderbolt : learning about lightning.
    Minneapolis, MN : Lerner, 1993. (How's the weather)
    ISBN 0-8225-2528-3 (5-7)
  • Kahl, Jonathan D.W. Weather watch : forecasting the weather.
    Minneapolis, MN : Lerner, 1996. (How's the weather)
    ISBN 0-8225-2529-1 (5-7)
  • Kahl, Jonathan D.W. Weatherwise : learning about the weather.
    Minneapolis, MN : Lerner, 1992. (How's the weather)
    ISBN 0-8225-2525-9 (5-7)
  • Kahl, Jonathan D.W. Wet weather : rain showers and snowfall.
    Minneapolis, MN : Lerner, 1992. (How's the weather)
    ISBN 0-8225-2526-7 (5-7)
  • Kerrod, Robin. The weather.
    New York : Marshall Cavendish, 1994. (Let's investigate science)
    ISBN 1-85435-630-5 (4-6)
  • Kramer, Stephen. Avalanche.
    Minneapolis : Carolrhoda Books, 1992.
    ISBN 0-87614-422-9 (4-6)
  • Kramer, Stephen. Eye of the storm : chasing tornadoes with Warren Faidley.
    New York : Putnam Pub. Group, 1999. ISBN 0-399-23029-2 (hc) (2-5)
    ISBN 0-698-11766-2 (pbk) (2-5)
  • Kramer, Stephen. Lightning.
    Minneapolis, MN : Carolrhoda Books, 1992.
    ISBN 0-87614-659-0 (4-6)
  • Kramer, Stephen. Tornado.
    Minneapolis, MN : Carolrhoda Books, 1992.
    ISBN 0-87614-660-4 (4-6)
  • Kramer, Stephen. Tornado : nature in action.
    Minneapolis, MN : Carolrhoda Books, 1997.
    ISBN 1-57505-058-7 (4-6)
  • Lee, Sally. Hurricanes.
    New York : Franklin Watts, 1993. (First books)
    ISBN 0-531-15665-6) (4-6)
  • Lye, Keith. Temperate climates.
    Austin, Tex. : Raintree Steck-Vaughn, 1997.
    ISBN 0-81724-827-7 (4-6)
  • Petty, Kate et Jakki Wood. Le ciel et ses mystéres.
    Saint-Lambert, Québec : Héritage, 1994
    ISBN 2-7130-1583-9 (4-6)
  • Petty, Kate and Jakki Wood. The sky above us.
    Hauppauge, NY : Barron's Educational Series, 1993. (Around and about)
    ISBN 0-8120-1234-8 (4-6)
  • Rosado, Maria. Blizzards! And ice storms. 1st ed.
    New York : Simon spotlight, 1999. (The Weather channel presents)
    ISBN 0-689-82016-X (pbk.) (4-6)
  • Science in the air. Presented by World Book Encyclopedia.
    Chicago, IL : World Book, 1998. (How and why science)
    ISBN 0-7166-7111-5 (pbk.) (4-6)
  • Sky watchers guide to weather.
    Downsview, Ont. : Environment Canada, Ontario Region, 1998.
    ISBN 0-662-27032-0 Catalogue no.: En 21-180/1998E (5-8)
  • Steele, Philip. Snow and ice.
    Austin, TX : Raintree Steck-Vaughn, 1998. (Living with the weather)
    ISBN 0-8172-5052-2 (4-6)
  • Suzuki, David. Looking at weather.
    Toronto : Stoddart, 1990.
    ISBN 0-7737-5141-6 (4-6)
  • Suzuki, David. Looking at weather. [sound recording].
    Toronto : CNIB, 1993. 1 cassette. (4-6)
  • Suzuki, David. La température.
    St.-Lambert, Québec : Les Éditions Héritage, 1991
    ISBN 2-7625-6406-9 (4-6)
  • Suzuki, David. You are the earth : from dinosaur breath to pizza from dirt.
    Vancouver : Greystone Books, 1999.
    ISBN 1-55054-751-8 (4-6)
  • Swanson, Diane. The day of the twelve story wave : grinding glaciers, howling hurricanes, spewing volcanoes, and other awesome forces of nature.
    Vancouver ; Toronto : Whitecap Books, 1995.
    ISBN 1-55110-374-5 (4-6)
  • Taylor, Barbara. Le temps et le climat.
    [adaptation française, Véronique Bussolin]
    Bonneuil-les-Eaux ,[France] : Gamma ; Montréal, Qué. : École active
    , [1997?].
    (Flash info) ISBN 2-71301-809-9 (Gamma).
    ISBN 2-890695484 (École active)
  • Taylor, Barbara. Wind and weather.
    New York : Franklin Watts, 1991. (Science starters)
    ISBN 0-531-14184-5 (4-6)
  • Taylor, Barbara. Weather and climate. 1st American ed.
    New York : Kingfisher Books, 1993. (Young discovers)
    ISBN 1-856-97940-7 (4-6)
  • Le Temps et la météo.
    Aartselaar, Belgique : Éditions Chantecler, 1989. (Regarde autour de toi)

    ISBN 2-8034-1772-3 (3-6)
  • Twist, Clint. Ice caps & glaciers.
    New York ; Toronto : Gloucester Press, 1992. (Hands on science)
    ISBN 0-531-17396-8 (4-6)
  • Twist, Clint. Hurricanes and storms.
    Danbury, CT : Children's Press, 1992. (Repairing the damage)
    ISBN 0-02-789685-4 (4-6)
  • VanCleave, Janice Pratt. Janice VanCleave's weather : mind-boggling experiments you can turn into science fair projects.
    New York : John Wiley, 1995. (Spectacular Science Projects)
    ISBN 0-471-03231-X (4-6)
  • Walker, Sally M. Water up, water down : the hydrologic cycle.
    Minneapolis, MN : Carolrhoda Books, 1992.
    ISBN 0-87614-695-7 (4-6)
  • Ward, Alan. Sky and weather.
    New York ; Toronto : Franklin Watts, 1993. (Project science)
    ISBN 0-531-14176-4 (4-6)
  • Weather's fury! a kid's guide to Xtreme forces[videorecording].
    (Hosted by Spencer Christian).
    Wynnewood, PA : Schlessinger Media, 1998.
    1 videocassette [25 min.]
    ISBN 1-57225-151-4 (4-7)
  • Wilson, Francis. The weather pop-up book.
    New York : Little Simon, 1987.
    ISBN 0-671-63699-5 (3-6)
  • Wilson, Francis. Le grand livre animé de la météo.
    [Saint-Lambert, Qué.] : Héritage, 1989. (Héritage jeunesse)

    ISBN 2-762-55242-3 (3-6)
  • Wood, Jenny. Storm.
    Austin, TX : Raintree Steck-Vaughn, 1993 (Violent earth)
    ISBN 1-56847-002-9 (3-7)
  • Wood, Jenny. Storms : facts, stories, projects.
    New York : Puffin Books, 1990.
    ISBN 0-14-034466-7 (4-7)
  • Wyatt, Valerie. Weather : frequently asked questions. Illus. by Brian Share.
    Toronto : Kids Can Press, 2000.
    ISBN 1-55074-582-4 (hc) or
    ISBN 1-55074-815-7 (pbk.) (3-5)
  • Wyatt, Valerie. Weather watch.
    Don Mills, Ont. : Addison-Wesley, 1990.
    ISBN 0-201154-04-8
  • Wyatt, Valerie. La météo.
    St.-Lambert, Québec : Les Éditions Héritage
    , 1991.
    ISBN 2-762-56563-4 (4-6)
  • Wyma, Brenda. Weather. Illus. by Diane Valko.
    Cypress, CA : Creative Teaching Press, 1995. (Investigations in science)
    ISBN 0-003-48280-2 (4-7)
  • Yolen, Jane. Weather report : poems selected by Jane Yolen.
    Honesdale, Penn. : Wordsong, 1993.
    ISBN 1-56397-101-1 (4-6)

Intermediate and Senior Grades 7-12

(Younger students will enjoy the illustrations.)

  • Canada. Environment Canada. Ice storm '98 : January 4-10, 1998. [Downsview,], Ont. : Environment Canada, Specialized Clients and Partners Branch, 1998 or 1999].
    Also available over the Internet at: ice_storm/index_e.cfm
  • Canada. Environnement Canada. Tempête du 4 au 10 janvier 1998. [Downsview], Ont. : Environnement Canada, Direction générale des services, les clients et les partenaires, [1998 ou 1999].
    Also available over the Internet at: ice_storm/index_f.cfm
  • Carpenter, Clive. The changing world of weather.
    New York : Facts on File, 1991.
    ISBN 0-8160-2521-5 (7-12)
  • Climate change presentation kit. [CD-ROM format].
    [Washington, D.C. : U.S. Environmental Protection Agency, 199-?]
    1 computer optical laser disc. Some files in PDF format ; slide presentation formatted to run on PowerPoint.
  • Cosgrove, Brian. Le temps qu'il fera. Paris : Gallimard, 1990.
    ISBN 2070565521 (7-12)
  • Cosgrove, Brian. Weather.
    Toronto : Stoddart, 1991. (Eyewitness books series)
    ISBN 0-7733-2461-3 (7-12)
  • Crowder, Bob. The wonders of weather. [Melbourne, Vict., Australia] : Bureau of Meteorology, 2000.
    ISBN 0-6423-7357-4
    (N.B.: This book contains excellent information on weather and weather patterns, but the reader should be aware that many of the concepts are described from the perspective of the Southern Hemisphere.)
  • Day, John A. Peterson first guide to clouds and weather.
    Boston : Houghton Mifflin, 1991.
    ISBN 0-395-56268-6 (7-Adult)
  • Global warming : hot times ahead? [videorecording]
    [Calif.?] : Churchill Films ; Edmonton : Access Network, 1990.
    1 videocassette (23 min.) Access Network ID No. BPN 331101 (7-Adult)
  • Gold, Susan Dudley. Blame it on El Niño. Expert review by David Adamec, NASA oceanographer.
    Austin, Tex. : Raintree Steck-Vaughn, 2000
    ISBN 0-7398-1376-5 (6-10)
  • Hodgson, Michael. Weather forecasting 2nd ed.
    Guildford, CT : Globe Pequat Press, 1999. (Basic essentials)
    ISBN 0-7627-0478-0 (7-10)
  • Kahl, Jonathan D. National Audubon Society first field guide. Weather.
    New York : Scholastic Press, 1998. ISBN 0-590-05469-4 (hc) or
    ISBN 0-590-05488-0 (pbk) (7-12)
  • Mason, John. Weather and climate.
    Morristown, NJ : Silver Burdett, 1991.
    ISBN 0-382-24255-4 (5-8)
  • McMillan, Bruce. The weather sky.
    New York : Farrar Straus Giroux, 1991.
    ISBN 0-374-38261-1 (6-12)
  • Murphree, Tom. Watching weather. Tom Murphree and Mary K. Miller with the Exploratorium.
    New York : Henry Holt & Co., 1998. (The accidental scientist)
    ISBN 0-8050-4542-2 (7-12)
  • Project ATMOSPHERE. Clouds : teacher guide.
    Washington, DC : Project ATMOSPHERE, American Meteorological Society,1993. (10 and up)
  • Project ATMOSPHERE. Global climate change (Teacher's guide). Washington, DC : Project ATMOSPHERE, American Meteorological Society, 1992. (10 and up)
  • Project ATMOSPHERE. Glossary of weather and climate with related oceanic and hydrologic terms.
    Boston, Mass. : Project ATMOSPHERE, American Meteorological Society,
    ISBN 1-878220-21-7 (10 and up)
  • Project ATMOSPHERE. Hazardous weather (Teacher's guide). Washington, DC : Project ATMOSPHERE, American Meteorological Society, 1992. (10 and up)
  • Project ATMOSPHERE. Look up! An atmosphere education source for teachers.
    Washington, DC : Project ATMOSPHERE, American Meteorological Society, 1992. (contains the Aug./Sept. 1992 issue of Weatherwise) (10 and up)
  • Project ATMOSPHERE. Water vapor : unseen weather. [videorecording].
    Washington, DC : Project ATMOSPHERE, American Meteorological Society, 1993. 1 videocassette (15min., 40sec.) (10 and up)
  • Project ATMOSPHERE. Water vapor and the water cycle (Teacher's guide). Washington , DC : Project ATMOSPHERE, American Meteorological Society, 1993. (10 and up)
  • Ramsey, Dan. Weather forecasting : a young meteorologist's guide. New York : McGraw-Hill (TAB Books), 1990. ISBN 0-8306-8338-0 (7-12)
  • Sciencepower 10 : science, technology, society, environment.
    Toronto : McGraw-Hill Ryerson, 2001.
    ISBN 0-07-560363-2 (9-12)
  • Tesar, Jenny E. Global warming.
    New York : Facts on File, 1991.
    ISBN 0-816-02490-1 (7-12)
  • Violent Earth. [CD-ROM format].
    Hove, East Sussex, England : Wayland Multimedia, 1995. 1 computer laser optical disc ; 1 User guide & curriculum notes.
  • Weather Channel (Television Station). Everything weather : the essential guide to the
    whys & wonders of weather
    . [CD-ROM format].
    Livonia, Mich. : The Weather Channel Education Dept., 1995, 1996.
    1 computer laser optical disc.
  • Watt, F. Weather and climate.
    Tulsa, OK : EDC (Usborne), 1992. (Science and experiments series)
    ISBN 0-88110-511-2 (pbk.), 0-7460-0683-7 (hard cover) (6-12)

Adult and Teacher Reference

  • Abley, Mark. The ice storm : an historic record in photographs of January 1998.
    Toronto : McClelland & Stewart, 1998.
    ISBN 0-7710-6100-5
  • Abley, Mark. Stories from the ice storm. (Edited by Mark Abley.)
    Toronto : McClelland & Stewart, 1999.
    ISBN 0-7710-0653-5 (bound)
    ISBN 0-7710-0654-3 (pbk)
  • Ahrens, C. Donald. Meteorology today : an introduction to weather, climate and the environment. 5th ed.
    St. Paul, MN : West Pub. Co., 1994.
    ISBN 0-314-02779-3
  • Allen, W.T.R. Wind and sea : state of sea photographs for the Beaufort wind scale = Le vent et la mer : photographies de l'état de la mer pour l'échelle de Beaufort. [Ottawa] : Environment Canada, Atmospheric Environment Service = Environnement Canada, Service de l'environnement atmosph l'environnement atmosphérique, 1983.
    ISBN 0-660-52328-0 Gov't Cat. No. En56-62/1983
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  • Berger, John J. Beating the heat : why and how we must combat global warming.
    Berkeley, CA : Berkeley Hills Books, 2000.
    ISBN 1-893-16305-9
  • Bluestein, Howard B. Tornado alley : monster storms of the Great Plains.
    New York, N.Y. ; Oxford, U.K. : Oxford University Press, 1999.
    ISBN 0-19-510552-4
  • Bowyer, Peter J. Where the wind blows : a guide to marine weather in Atlantic Canada.
    (Published in co-operation with Environment Canada).
    St. John's, Nfld. : Breakwater Books Ltd., 1995.
    ISBN 1550811193
  • Burroughs, William James. The climate revealed.
    Cambridge, U.K. ; New York : Cambridge University Press, 1999.
    ISBN 0-521-77081-5
  • Canada. Environment Canada. Ontario Region. Clouds. [wall chart] [Downsview, Ont.] : Environment Canada, Ontario Region, Commercial Services Branch, [1999]. ISBN 0-662-27621-3
    Gov't. Cat. No. En56-134/1999E
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    ISBN 0-662-83539-5
    No. gouv. de cat. No. En56-134/1999F
  • Canadian Geographic. Mysteries in the ice : secrets of the past in Canada's glaciers.
    [Toronto, Ont.] : Summerhill Entertainment, 2000.
    1 videocassette (47 min.)
    ISBN 1-894524-03-9
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    [Scarborough, Ont.] : Baton CTV News, 1998.
    1 videocassette [36 min.]
  • Crépeau, Pierre. Pointing at the wind : the weather-vane collection of the Canadian
    Museum of Civilization
    . with the assistance of Pauline Portelance. Hull, Quebec : Canadian Museum of Civilization, 1990.
    ISBN 0-660-12904-3.
    Gov't Cat. No. NM98-3/68-1990E
  • Crépeau, Pierre. Signes des vents : la collection de girouettes du Musé canadien des
    . avec le concours de Pauline Portelance.
    Hull, Québec : Musé canadien des civilisations, 1990.

    ISBN 0-660-90296-6
    Gov't. Cat. No. NM98-3/68-1990F
  • DeBlieu, Jan. Wind : how the flow of air has shaped life, myth, and the land.
    Boston : Houghton Mifflin, 1998.
    ISBN 0-395-78033-0
  • Dunlop, Storm. A dictionary of weather.
    Oxford : Oxford University Press, 2001.
    ISBN 0-19-280063-9
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    Willowdale, ON : Firefly Books, 1995.
    ISBN 1-895565-64-2
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    New York ; Oxford : Oxford University Press, 1996. ISBN 0-19-509485-9 (set)
  • Engelbert, Phillis. The complete weather resource. (4 vol. set)
    Detroit, Mich. : UXL, 1997-2000.
    ISBN 0-8103-9787-0 (set)
  • Faidley, Warren. Storm chaser [videorecording].
    Atlanta : Weather Channel, 1996.
    1 videocassette (55min.)
  • Faidley, Warren. Storm chaser : in pursuit of untamed skies.
    Atlanta : Weather Channel, 1996.
    ISBN 1-888763-00-0
  • Fleming, James Rodger. Historical perspectives on climate change. New York ; Oxford : Oxford University Press, 1998. ISBN 0-19-507870-5
  • Freier, G. D. Weather proverbs : how 600 proverbs, sayings, and poems accurately explain our weather . rev. ed.
    Tucson, AZ : Fisher Books, 1992.
    ISBN 1-55561-045-5
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    New York : Random House, 1999.
    ISBN 0-517-20194-1
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    New York : Alpha Books ; Distr. by Macmillan, 1999. ISBN 0-02-862709-1
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    New York : Scientific American Library, 1995.
    ISBN 0-7167-5049-X
  • The Great Lakes marine weather kit for safe boating[multimedia].
    [Downsview, Ont. ; Hamilton, Ont.] : Environment Canada, Ontario Region, 1998.
    1 videocassette, 1 vol.
    ISBN 0-660-17262-3 (set).
    Gov't Cat. No. En56-125/1-1998E.
  • Haggerty, Don. Rhymes to predict the weather.
    Seattle, WA : Springmeadow Publishers, 1985.
    ISBN 0-9614703-0-5
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    Montreal, Que. : National Film Board of Canada, 1996.
    1 videocassette (48 min., 43sec.) Cat. No. 9196-017
  • Heidorn, Keith. The Weather Doctor's almanac 2000.
    Victoria, B.C. : Spectrum Educational Enterprises, 2000.
  • Heidorn, Keith. The Weather Doctor 1998. [electronic publication] Victoria, B.C. : Spectrum Educational Enterprises, 2000.
  • Hengeveld, Henry. Understanding atmospheric change.
    Ottawa : Environment Canada, 1991. (SOE Report No. 91-2)
    ISBN O- 662-18687-7 : SSC Cat, No. EN1-11/91-2E
  • Hengeveld, Henry. Comprendre l'atmosphère en évolution.
    Ottawa : Environnement Canada, 1992. (Rapport EDE No. 91-2)
    ISBN 0-662-96769-0 ; SSC Cat. No. EN1-11/91-2F
  • Hodgson, Michael. Weather forecasting. 2nd ed. Illus. by Devin Wick. Old Saybrook, Conn. : Globe Pequot Press, 1999. (Basic essentials)
  • Hurricane! [videorecording]. Written, produced and directed by Larry Eagle and Thomas Lucas, for WGBH EF Television in Boston, Mass.
    [Livonia, Mich. : The Weather Channel], 1989. (Nova television program) 1 cassette [60 min.]
    ISBN 1-88473-864-8 (Caution : some disturbing images)
  • "Hurricane" : a familiarization booklet. Rev ed.
    [Silver Springs, MD] : U.S Dept. of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, 1993.
    Gov't pub. No. NOAA PA 91001
  • Images of meteorology. [CD-ROM format].
    [Edinburgh : Dept. of Meteorology, University of Edinburgh, 1996?]
    1 computer laser optical disc. Information on software found at:
  • Kramer, Stephen P. Eye of the storm : chasing storms with Warren Faidley. Photographs by Warren Faidley.
    New York : G.P. Putnam's & Sons, 1997.
    ISBN 0-399-23029-7
  • Lange, Owen S. The wind came all ways : a quest to understand the winds, waves and
    weather in the Georgia Basin
    Vancouver, B.C. : Environment Canada, Atmospheric Environment Service, 1998.
    ISBN 0-660-17517-7. Gov't Cat. No. En56-74/1998E.
  • Lehr, Paul E., et al. Weather : air masses, slouds, rainfall, storms, weather maps, climate.
    New York : Golden Books, 1987. (Golden guides) ISBN 0-307-24051-7
  • Lockhart, Gary. The weather companion : an album of meteorological history, science, legend, and folklore.
    New York : John Wiley & Sons, 1988.
    ISBN 0-471-62079-3
  • Ludlum, David M. National Audubon Society field guide to North American weather.
    New York : A.A. Knopf : Distr. By Random House, 1991. (National Audubon Society field guide series) ISBN 0-6794-0851-7
  • Lyons, Walter A. The handy weather answer book.
    Detroit, MI : Visible Ink Press, 1997.
    ISBN 0-7876-1034-8
  • Miller, Albert. Elements of meteorology. 4th ed. Reprint ed.
    Columbus, OH : C.E. Merrill Pub. Co., 1983.
    ISBN 0-318-39709-9
  • Monmonier, Mark. Air apparent : how meteorologists learned to map, predict, and dramatize weather.
    Chicago, ; London, : University of Chicago Press, 1999.
    ISBN 0-226-53422-7
  • National Film Board of Canada. The northern lights[videorecording].
    Edmonton, : National Film Board (distributor), 1992.
    1 videocassette (48 min., 38 sec.) Cat. No. 9192-041
  • National Geographic Society. Cyclone![videorecording].
    Washington, DC : National Geographic Society, 1995.
    1 videocassette (ca. 60 min.)
    ISBN 0-7922-1979-1
  • National Geophysical Data Center (U.S.). 1998 Atlantic hurricanes. [slide set]
    Boulder, CO : National Geophysical Data Center, 2000. (20 slides)
    NOAA/NGDC product code # GO1940-SLI-A0001
  • National Geophysical Data Center (U.S.). 1998 Northwest Pacific hurricanes. [slide set]
    Boulder, CO : National Geophysical Data Center, 2000. (18 slides)
    NOAA/NGDC product code # GO1943-SLI-A0001
  • National Geophysical Data Center (U.S.). The most intense tropical storms of 1998. [wall poster]
    Boulder, CO : National Geophysical Data Center, 2000. (14 images, 2' x 3')
    NOAA/NGDC product # GO1937-POS-A0001
  • Organisation météorologique mondiale. Une décennie contre les catastrophes.
    Genève, Suisse : OMM, 1994. [OMM No. 799]

    ISBN 92-63-20799-2
  • Organisation météorologique mondiale. En première ligne : Les services
    météorologiques publics
    Genève, Suisse : OMM, 1994. [OMM No. 816]

    ISBN 92-63-20816-6
  • Organisation météorologique mondiale. Météo et sports.
    Genève, Suisse : OMM, 1996. [OMM No. 835]

    ISBN 92-63-20835-2
  • Organisation météorologique mondiale. Observer l'environnement de la planète :
    le temps, le climat, l'eau
    Genève, Suisse : OMM, 1994. [OMM No. 796]

    ISBN 92-63-20796-8
  • Organisation météorologique mondiale. L'OMM et le réchauffement mondial.
    Genève, Suisse : OMM, 1990. (OMM No. 741)

    ISBN 92-63-20741-0
  • Organisation météorologique mondiale. Le temps, le climat et la santé.
    Genève, Suisse : OMM, 1999. (OMM No. 892)

    ISBN 92-63-20892-1
  • Pembina Institute for Appropriate Development. The Canadian environmental education catalogue : a guide to selected resources and materials.
    Drayton Valley, Alta. : The Pembina Institute, 1991. ISBN 0-921-71907-8
  • Pembina Institute for Appropriate Development. Who's who in environmental education.
    Drayton Valley, Alta. : The Pembina Institute, 1993.
  • Phillips, D.W. Blame it on the weather : strange Canadian weather facts.
    Toronto, Ont. : Key Porter, 1998.
    ISBN 1-55013-968-1
  • Phillips, D.W. Canadian weather trivia calendar.
    Downsview, Ont. : Environment Canada, 2001.
  • Phillips, D.W. L'Almanach météorologique canadien.
    Downsview, Ont. : Environment Canada, 2001.
  • Phillips D.W. The climates of Canada.
    Ottawa, Ont. : Environment Canada, 1990.
    ISBN 0-660-13459-4
  • Phillips D.W. Les climats du Canada.
    Ottawa, Ont. : Environnement Canada, 1990.
    ISBN 0-660-92845-0
  • Phillips D.W. The day Niagara Falls ran dry! Canadian weather facts and trivia.
    Toronto, Ont. : Key Porter Books, 1993.
    ISBN 1-55013-491-4
  • Pielke, Roger A. Hurricanes : their nature and impacts on society.
    Roger A. Pielke , Jr. And Roger A. Pielke, Sr.
    New York : John Wiley & Sons, 1997.
    ISBN 0-471-97354-8
  • Pommainville, Pierre. AWARE : aviation weather . playing by the rules.
    [Saint-Laurent, Qué] : Environment Canada, Quebec Region, 1996.
    ISBN 0-660-16445-0.
    Gov't Cat. No. En56-84/1996E.
  • Pommainville, Pierre. MÉTAVI : tout sur les règles du jeu en météo aviation.
    [Saint-Laurent. Qué.] : Environnement Canada, Région du Québec, 1996.

    ISBN 0-660-95253-X. Gov't Cat. No. En56-84/1996F.
  • Posey, Carl A. The living earth book of wind & weather.
    Pleasantville, NY ; Montreal : Readers' Digest Association, Inc., 1994.
    ISBN 0-89577-625-1
  • Resources in Earth Observation. [CD-ROM format]
    Canberra, Australia : CSIRO Office of Space Science & Applications, 1996-
    1 disc issued annually.
  • Reynolds, Ross. Cambridge guide to the weather.
    Cambridge ; New York : Cambridge University Press, 2000.
    ISBN 0-521-77489-6
  • Rosenfeld, Jeffrey O. Eye of the storm : inside the world's deadliest hurricanes, tornadoes, and blizzards.
    New York : Plenum Press, 1999.
    ISBN 0-306-46014-9
  • Rubin, Louis D. The weather wizard's cloud book : how you can forecast the weather accurately and easily by reading the clouds. Louis D. Rubin and Jim Duncan.
    Chapel Hill, N.C. : Algonquin Books, 1984, 1989. ISBN 0-912-69710-5
  • Schaefer, Vincent. A field guide to the atmosphere.
    Boston : Houghton Mifflin, 1981. 1983. (Peterson field guide series, no. 26)
    ISBN 0-395-24080-8 and ISBN 0-395-33033-5
  • Scorer, Richard. Spacious skies. Photos by Arjen Verkaik.
    London : David & Charles, 1989.
    ISBN 0-7153-9139-9
  • Sorbjan, Zbigniew. Hands-on meteorology : Stories, theories and simple experiments.
    Boston, Mass. : American Meteorological Society, 1996.
    ISBN 1-87220-20-9
  • Soul of the sky : exploring the human side of weather. Edited and compiled by Dave Thurlow and C. Ralph Adler.
    North Conway, NH : Mount Washington Observatory, 1999.
    ISBN 0-931134-99-4
  • Stevens, William K. The change in the weather : people, weather, and the science of climate.
    New York : Delacorte Press, 1999.
    ISBN 0-385-32012-4
  • Stull, Roland B. Meteorology for scientists and engineers. 2nd ed. Pacific Grove, CA : Brooks/Cole Thomson Pub., 2000.
    ISBN 0-534-37214-7
  • Tornado! Hurricane! Flood! : wonders of weather[videorecording].
    Discovery Communications, Inc., 1996.
    1 videocassette [ca. 60 min.]
    ISBN 1-5633-457-6
  • Tornado video classics : the ultimate tornado experience. [videorecording] Edited version.
    [St. Johnsbury, VT] : Environmental Films, 1994.
    1 videocassette [ ca. 90 min] (Caution : some disturbing images)
  • La trousse d'information sur les conditions météorologiques maritimes sur les Grands Lacs pour la sécurité nautique[ensemble multi-supports].
    [Downsview, Ont. ; Hamilton, Ont.] : Environnement Canada, Région de l'Ontario, [1998].
    1 videocassette, 1 v.
    ISBN 0-660-95817-1 (complet).
    Gov't Cat. No. En56-125/1-1009F
  • Verkaik, Arjen. Manuel de l'observateur de temps violent. Éd. Rev. Elmwood, Ont. : Whirlwind Books, 2000.
    ISBN 0-9681537-3-9
  • Verkaik, Arjen. Severe weather watcher handbook. Rev. ed.
    Elmwood, Ont. : Whirlwind Books, 2000.
    ISBN 0-968153702-0
  • Verkaik, Arjen. Le vent, les temps, les vagues : guides des conditions météorologiques
    maritimes sur les Grands Lacs
    . (Aussi inclus dans: La trousse d'information sur les conditions météorologiques maritimes sur les Grands Lacs pour la sécurité nautique).
    [Downsview, Ont. ; Hamilton, Ont.] : Environnement Canada, Région de l'Ontario, 1998.
    ISBN 0-660-95936-4.
    Gov't Cat. No. En56-125/2-1998F.
  • Verkaik, Arjen. Wind, weather & waves : a guide to marine weather in the Great Lakes
    . (Also included with: The Great Lakes marine weather kit for safer boating).
    [Downsview, Ont. ; Hamilton, Ont.] : Environment Canada, Ontario Region, 1998.
    ISBN 0-660-17436-7.
    Gov't Cat. No. En56-125/2-1998E.
  • Verkaik, Jerrine. Under the whirlwind : everything you need to know about tornadoes but didn't know who to ask.
    Elmwood, Ont. : Whirlwind Books, 1997.
    ISBN 0-9681537-0-4
  • Watts, Alan. The weather handbook. 2nd ed.
    Dobbs Ferry, NY : Sheridan House, 1999.
    ISBN 1-574-09081-X
  • Weather Channel (Television Station). Hurricane tracking kit.
    [Livonia, Mich.] : the Weather Channel, [199-?]
    1 map, 1 black felt-tipped marking pen.

  • Weather tracker's kit : explore the changing forces of nature. CD-ROM ed. Philadelphia, PA : Running Pr., 1995. ISBN 1-56138-641-3
    1 computer laser optical disc ; 1 handbook, ;1 observation weather station,
    1 cloud chart. (Handbook written by Gregory C. Aaron.)
  • Weather tracker's kit : exploring the changing forces of nature. (Discovery kit series) Philadelphia, PA : Running Pr., 1991.
    ISBN 0-87471-998-X
    1 handbook ; 1 observation station ; 1 cloud chart.
    (Handbook written by Gregory C. Aaron.)
  • Wheaton, Elaine. But it's a dry cold : weathering the Canadian Prairies. Calgary : Fifth House Publishers, 1998.
    ISBN 1-894004-01-9
  • Williams, Jack. The weather book. 2nd.ed.
    New York : Vintage Books ; Toronto : Random House of Canada, 1997.
    ISBN 0-679776-65-6
  • World Meteorological Organization. Climate and human health. Geneva, Switzerland : WMO, 1996. (WMO No. 843)
    ISBN 92-63-10843-9
  • World Meteorological Organization. A Decade against natural disasters.
    Geneva, Switzerland : WMO, 1994. [WMO No. 799] ISBN No. 92-63-10799-8
  • World Meteorological Organization. Observing the world's environment : weather, climate & water.
    Geneva, Switzerland : WMO, 1994. [WMO No. 796] ISBN 92-63-10769-3
  • World Meteorological Organization. On the front line : Public Weather Services.
    Geneva, Switzerland : WMO, 1994. (WMO No. 816) ISBN 92-63-10816-1
  • World Meteorological Organization. Weather and sports.
    Geneva, Switzerland : WMO, 1996. (WMO No. 835) ISBN 92-63-10835-8
  • World Meteorological Organization. Weather, climate and health.
    Geneva, Switzerland : WMO, 1999. (WMO No. 892) ISBN 92-63-10892-7
  • World Meteorological Organization. WMO and global warming.
    Geneva, Switzerland : WMO, 1990. (WMO No. 741) ISBN 92-63-10741-6
  • World Meteorological Organization. WMO and the ozone issue.
    Geneva, Switzerland : WMO, 1992. (WMO No. 778) ISBN 92-63-10778-5

Internet Websites on Weather and Science

  • Specific Sites on Weather-Related Topics and Publications
  • Bilingual Environment Canada Weather site, showing current conditions across the country, local 7-day forecasts, satellite imagery, etc.
  • : Environment Canada, All Regions Fact Sheets on weather and climate-related topics.
  • : Canadian Meteorological and Oceanographic Society homepage contains a link under Education - Schools to a series of classroom activites about Weather by Dave Phillips.
  • : Great all-round Meteorology Education site from University of Illinois at Urbana-Champaign.
  • : American Meteorological Society site has a program on Weather Education for grades K-12.
  • The Weather Doctor's website by Keith Heidorn is a great site for interesting information on weather events and phenomena, people in weather, effects of weather, book reviews, etc.
  • A great website for kids from the University Corporation for Atmospheric Research. Lots of activities and information.
  • The U.S. National Snow and Ice Data Center has links to some great educational sites dealing with snow, ice, glaciers and polar regions. Kids will have lots of fun "playing in the snow" here.
  • NOAA site gives excellent background information and current status of El Nino and La Nina.
  • El Nino site also provides links to several other El Nino Educational Sites.
  • Excellent hurricane database.
  • : Excellent site for tornado information.
  • : Interesting site shows what the weather is normally like in thousands of places world-wide.
  • One of the best all-round weather education sites with explanations in easily understandable terms. Also gives world weather conditions and forecasts.
  • : An excellent site with lots of information relating to the Great Lakes themselves and the surrounding region.

Resource Sites for Teachers

  • : The CBC's website for teachers includes some excellent information and resources.
  • : This website from Alberta includes ideas for teachers and provides links to other sites with lesson plans and other activities.
  • : U. S. National Weather Service, Central Region's Education website with weather information and lesson plans for teachers.
  • : NOAA's website for teachers includes information on weather, climate change, oceans and satellites, and gives links to many other useful sites.
  • The Education and Outreach website from the University Corporation for Atmospheric Research has great tips for teachers and lesson plans for all grade levels from K-12.
  • The "Explores" website provides links to sites providing curricula information and learning activites.
  • : The Australian Bureau of Meteorology website contains a comprehensive educational section on weather . Of special interest to students and teachers, and also the general public.
  • : An exciting site that lets you design your own snowflake or learn about the Doppler effect, among many other experiments.
  • : The Great Canadian Scientists page with the "Ask a Scientist" feature.

Useful National and International Meteorology-Related Sites

  • Environment Canada's "Green Lane" with links to Regional Offices and EC publications.
  • : Meteorological Service of Canada homepage with links to its services and publications.
  • : U.S. National Oceanic and Atmospheric Administration (NOAA) homepage with links to many different services and current issues.
  • British Met. Office homepage with information on weather in Britain, Europe and around the world.
  • : Météo France homepage with information on local weather and links to other European weather sites.
  • (In French only): Australia's Bureau of Meteorology homepage, with weather information from the Southern Hemisphere.
  • : World Meteorological Organization (WMO) homepage with links to many different national weather services around the world.

Return to Table of Contents

Return to Table of Contents

Air Quality Supplement

Download Air Quality Supplement (PDF; 595 KB)

In this chapter

Air Pollution, Smog and Our Air Quality

Every living thing on earth needs air: plants, trees, animals, birds, humans and everything in between. The air we breathe is made up of different gases (78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, 0.03 percent carbon dioxide and the remaining 0.07 percent a mixture of hydrogen, water, ozone, neon, helium, krypton, xenon and other trace components). In order for us to survive, we require oxygen (O2). In order for plants to survive, they need a different gas, called carbon dioxide (CO2). When we breathe, our lungs take in all the gases in the air around us. Thus it is important for the future of our planet, and the health of all living things, that we do what we can to reduce air pollution.

What Is Smog?

As you know, the air around you is invisible. You can't see yourself take in these gases. Most of the pollution in the air is also invisible. Sometimes, especially if you live in a large city, pollution concentrations can be high enough that you can actually see the pollution in the air. Pollution, whether visible or invisible, is also known as smog.


To illustrate to your students the difference between visible and invisible pollution, try Activity number 1

The term smog originally described a mixture of smoke and fog in the air. Now it is used to describe a mixture of pollutants. This mixture can often be seen as a brownish-yellow or greyish-white haze in the air. The two key components of smog are particulate matter (PM), also known as airborne particles, and ground-level ozone (O3). Other pollutants include sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), and hydrogen sulphide (H2S).


Fast Fact: Motor vehicle exhaust contains five of the components of smog: carbon monoxide, particulate matter, lead, nitrogen oxides, and volatile organic compounds.

Particulate Matter (Airborne Particles)

Particulate matter (PM) is made up of very tiny solid or liquid particles that are small enough to remain suspended in the air. Scientists separate the particles into two categories, depending on their size. Coarse particles, referred to as PM10, are under 10 micrometres in size. A micrometre is 1 millionth of a metre. Coarse particles are 1/8th the size of a human hair. The fine particles, which are less than 2.5 micrometres in size, are in the category referred to as PM2.5. These particles are smaller than a single particle of flour.

Diagram: The relative size of beach sand, a grain of flour, and a fine particle

Image 21. The relative size of beach sand, a grain of flour, and a fine particle less than 2.5 microns.

Particulate matter includes dust, dirt, soot, smoke and tiny particles of chemical pollutants. The major sources of particulate pollution are factories, power plants, trash incinerators, motor vehicles, construction activity, fires and natural dust blown around by the wind. The amount of particulate matter in the air can be worse in winter because we burn wood and other fuel to heat our houses, releasing tiny particles of pollutants. In big cities, where there are lots of cars, particulate matter can be worse than in rural areas where there are fewer cars. The amount of particulate matter can also be greater in places where there are lots of factories and industries that release pollutants into the air.

activity pad and pen

Activity: Particulate matter in the air can be collected. Have your students cover the outside of a small jar, or a small square of plastic, with petroleum jelly and place it outside. Leave it for 24 hours and then observe the dirt particles that were collected. It may be helpful to place a piece of white paper behind and/or use a magnifying glass. Several of these set-ups can be placed in different areas around the school or at home to see which area will collect the most particles.


Fast Fact: 20 percent of homes in Canada use wood as a secondary heating source. That number is higher in Atlantic Canada.

Ground-Level Ozone

Ozone is the same gas, whether it is high up in the atmosphere or near the ground. In the stratosphere, ozone forms a protective barrier for harmful radiation from the sun (Refer to pages 12 and 44 in the Sky Watchers: Guide to Weather for more information). Near the ground, ozone is considered a pollutant and can be harmful to people, animals, plants and other materials.

Diagram: Oxygen, O2 is two oxygen atoms bonded together. The formula for ozone is O3 which is three oxygen atoms.

Image 21. Oxygen, O2 is two oxygen atoms bonded together. The formula for ozone is 03, which is three oxygen atoms.

Unlike particulate matter, ozone is generally a colourless gas and cannot be seen in the air. However, at very high concentrations, ozone can have a bluish tinge. Ground-level ozone is referred to as a secondary pollutant. This means it is formed from other pollutants already present in the air. The other pollutants, mainly nitrogen oxides (NOx) and volatile organic compounds (VOCs), react with oxygen and energy from the sun to produce ground-level ozone. Because sunlight is required to form ozone, the concentrations in the air are normally higher in the summer, when temperatures are warmer and the sun's rays are stronger.


Tips: To help your students better understand the role of the sun in forming ozone, you may want to use a comparison with making Rice Krispie squares. Without heat to melt the marshmallows, you have no squares. The other pollutants will not form ozone without the energy from the sun to start the reaction.


You may want to revisit Activity 1  in the Sky Watchers: Guide to Weather about the sun's rays relative to the earth's rotation to illustrate the difference in the strength of the sun during different seasons.

The pollutants that are "cooked" to make ozone are formed by both man-made and natural sources. Nitrogen oxides are produced whenever natural gas, gasoline, diesel fuel, kerosene and oil are combusted; the sources include cars, trucks, power plants and factories. They are also released into the air by nature during forest fires and by volcanoes. VOCs are produced whenever the fuels above evaporate into the air. VOCs are also released directly to the atmosphere by trees.

activity pad and pen

Activity: To demonstrate the pollution from burning, light a candle and pass the bottom of a white glass plate through the flame. There should be a dark mark on the bottom of the plate where the flame touched. This is the pollution released from the burning of the wax.


Note :
To monitor the ground-level ozone concentrations in your area, try Activity 2

Diagram: Smog trapped in Fraser Valley

Image 22. Smog Trapped in Fraser Valley: Classical smog behaviour in the Fraser Valley.

Smog Behaviour

Local Meteorology

Local weather conditions play a major role in the movement of air pollution. The severity of air pollution can be increased when local wind conditions and/or the unique topography of a region cause the pollutants to become trapped in a layer of relatively still air. Ground-level ozone is usually formed when there is a slow-moving high pressure system influencing the area providing stronger

sunlight and warmer temperatures. Typically, the warmer air will rise and the pollution will be dispersed by the wind. However, pollution can be trapped near the ground when a temperature inversion occurs. What is a temperature inversion? Well, normally the temperature decreases in the troposphere with height. A temperature inversion will form when the temperature increases with height resulting in a stable layer of air. This stable layer acts as a "lid" on the lower atmosphere, resulting in an environment more susceptible to higher pollution concentrations. When this occurs, the winds are light, and the pollution becomes trapped. In southern British Columbia, the delicate interaction between the local topography and the Pacific Ocean is especially important. These features, coupled with a strong temperature inversion, frequently result in atmospheric conditions favorable for elevated ground-level ozone episodes. For example, several cities, including the greater Vancouver region, lie within the Fraser Valley where the mountain walls trap the air. These unique geographical features, along with sea-to-shore breezes off the Strait of Georgia, promote the formation of a temperature inversion. As a result, air-flow patterns become restricted and help to contribute to the area's ozone problem. The air is often polluted by automobile exhaust and other sources and is trapped close to the ground where we breathe it in.

Long-Range Transport

In Chapter 2 of the Sky Watchers Guide to Weather, you learned about the global wind patterns that travel around the earth. Pollution may be carried around the earth by these winds. The pollution that is generated in one place is transported by the wind and can affect people in other areas. Ground-level ozone and other pollutants can travel long distances, from hundreds to a few thousand kilometres in a single day. During this travel, pollutants can be deposited on the ground or on buildings, and undergo chemical changes. These chemical changes can result in an entirely different pollutant being formed. Volatile organic compounds and nitrogen oxides, for instance, may react with oxygen and energy from the sun to form ground-level ozone that will ultimately affect another area. There is always someone downstream of where pollution is released.


Note :
Have your students try Activity 3, The Clean Air Game, in the Activities section. It will help them to remember the concepts and vocabulary covered so far.

Effects Of Pollution

Health Effects

Our lungs inhale all the things in the air around us, including particulate matter and ground-level ozone. Elderly people and those with heart or lung disease - such as asthma, emphysema and chronic bronchitis - are particularly sensitive to air pollutants. When pollution levels are high, sensitive people may experience symptoms after only one or two hours outdoors. Children and active adults are also at a greater risk because they typically spend more time outside and engage in physical activities that increase their heart rate. Also, children tend to be more sensitive than adults because they require more air and thus breathe faster than adults - twice as much air per pound of body weight compared to adults (Journal of Environmental Health Perspectives).

Principal Ozone Problem Areas in Canada

Maritime Provinces:
New Brunswick, Nova Scotia and Prince Edward Island receive air pollution from the Lower Great Lakes region, Southern Quebec and the eastern seaboard of the United States. Cross border pollution, due to long-range transport, is the major contributor to this region's smog problem.
Windsor-Quebec City Corridor:
This heavily populated corridor covers a strip about 100 km wide along the Canadian border, extending from Windsor through Toronto and Montreal to Quebec City. This area experiences high levels of ozone more often and for longer periods than any other part of the country. While much of the smog here is generated locally, air pollution transported from the United States contributes significantly to ground-level ozone in the region.
Lower Fraser Valley:
This valley, which includes the City of Vancouver, is bordered by the Coastal Mountains to the north and the Cascade Mountains to the southeast. These unique geographical features, along with the sea-to-shore breezes off the Strait of Georgia, restrict air-flow patterns and contribute to the area's ozone problem. Here, the majority of the smog is generated locally. Motor vehicles in the Vancouver area are one of the major sources of smog in this region.

Fast Fact: According to the Canadian Lung Association, one in five Canadians now has some form of respiratory problem and 5 to 10 percent of Canadian children have childhood asthma.

Exposure to ozone can irritate the nose and throat and cause chest tightness, coughing and wheezing. Increases in ozone levels in Canada have been linked to increased mortality, emergency hospital visits and admissions for respiratory problems. In sensitive people, the stress of ozone exposure can be particularly damaging. There is also evidence that ozone heightens the sensitivity of asthmatics to allergens. Other studies on animals have indicated that ozone exposure decreases the lungs' ability to ward off disease. The effects also include decreased lung capacity, which can impair performance in athletes.


Note :
Students can simulate the experience of those with asthma and other respiratory problems with Activity 4 in the Activities section.

Many of the adverse health effects resulting from exposure to particulate matter are similar to those for ozone, and are specific to the cardio-respiratory (heart-lung) system. When we inhale particulate matter, the particles can penetrate deep into the lungs. The smaller the particle, the deeper into the lungs it can penetrate. Recent studies have identified strong links between high levels of airborne particles and increased hospital admissions for heart and respiratory problems, as well as higher death rates from these ailments.


Fast Fact: According to a report commissioned by the Ontario Medial Association (OMA), air pollution costs Ontario citizens more than $1 billion a year in hospital admissions, emergency room visits and absenteeism. Approximately 1900 premature deaths occur per year in Ontario as a result of air pollution.

Other Effects of Pollution

Plants also require air to grow. Ozone interferes with the ability of plants to produce and store food. That means that growth and reproduction are threatened along with weakening the overall health of the plant so they may be more susceptible to disease and pests. Some estimate that the provinces of British Columbia and Ontario each lose millions of dollars per year because of lower crop productivity due to high levels of ground-level ozone. Ozone damage can be seen on the foliage of some potato varieties in Atlantic Canada. Beans, tomatoes, potatoes, soya beans and wheat are all crops which are sensitive to ozone. Trees, which live longer than the plants above, are exposed to ozone year after year. If the effects of exposure add up over many years, which is believed to happen, entire forests can be affected. This means that other things, like the plants and animals that depend on the trees to provide shelter, are also affected by prolonged exposure to ground-level ozone.


Fast Fact: Rural pollution can be just as bad as urban pollution, depending on a combination of local weather conditions, topography, or the amount of pollution due to long-range transport.

Other materials you use in everyday life can be weakened by exposure to high levels of ozone. Rubber, textile dyes and fabrics, and certain types of paints and other coatings are either damaged or weakened by ozone exposure. Synthetic elastic materials can become brittle and crack, while the textiles and dyes fade faster than usual.


Note :
To demonstrate the effect of pollution on rubber, try Activity 5 in the Activities section.

Air Quality Prediction

As Sky Watchers, you have learned how Environment Canada meteorologists predict what the weather is going to be like where you live. You also know they predict how strong the UV radiation is going to be for the day. This is done so Canadians can be better prepared for any kind of weather, and can wear sunscreen and protective clothing to prevent sunburns. Environment Canada and your provincial, regional and local governments are also concerned about the air you breathe and the quality of that air. They want people to be able to make informed decisions and plan their activities around the quality of the air. In some cities, like Vancouver and Montreal, the local municipal governments are responsible for issuing the smog information for the local area. Just like you wouldn't plan to have a picnic in the rain, or fly a kite in the middle of a thunder and lightning storm, it is better to avoid strenuous outdoor activities when pollution levels are high. Generally, the highest levels of ozone are in the mid-to-late afternoon. If you want to have a game of soccer, where you will be running around a lot and breathing in a lot more air, depending on the specific conditions for the day, you should try and play in the morning, when the air quality is generally better. The forecast tells you when the air quality will be good or bad, so you can plan your outdoor activities around it.


Tips: For more information on Air Quality Forecasts and Services in your area, login to our website at Air Quality Health Index and select your region from the map.

Smog Alerts

Federal, provincial, regional and local governments are working together to keep Canadians informed about the level of air pollution in their communities, and to educate them about how to reduce smog and limit their exposure. Listen for the following:

Smog or Air Quality Advisories:
Environment Canada, in partnership with provincial & municipal agencies, issue advisories in smog-prone communities across the country. These advisories, usually issued the day before high levels of ozone are expected, encourage people and industries to take action to reduce air pollution. Information is also provides about the effects of smog on the environment and human health.
Air Quality Index:
In some areas, an Air Quality Index (AQI) is issued by the province or local municipality to provide daily information on various air pollutants. Some provinces also use this as a basis to predict air quality. Contact your provincial or local government for more details.
Smog Forecast:
In 1997, a pilot project forecasting smog levels on a daily basis was launched in Saint John, NB. This initiative, which was very successful, was developed in partnership with the provincial government and health organizations. Environment Canada has now expanded this service across NB, NS, and PEI and is working to involve other provinces by building on existing programs and partnerships.

To reduce your exposure to smog, listen for Smog Advisories and other air quality information. Avoid vigorous outdoor exercise when levels of ground-level ozone and airborne particles are high. People with heart and lung disease, especially asthma, should stay indoors if possible.

Smog Forecasts

The categories for the smog forecasts range from good to very poor. In Atlantic Canada and the greater Vancouver area for instance, the categories are good, fair, poor and very poor. In Ontario, the lower categories are further divided into very good, good and moderate. When the forecast is fair, health officials recommend that people who are sensitive to pollution should try to restrict their activity and stay indoors.


Fast Fact: Saint John, NB was the first city in Canada to have a daily smog forecast. The forecast has been operating since 1997.

Most smog forecast programs operate between May and October. The concentrations of ground-level ozone are usually higher during this period due to warmer weather conditions. The number of times each summer that the higher levels are reached depends on where you live, weather conditions and can vary from year to year. If the summer is cool and wet, there will be fewer days with high smog levels. On the other hand, a hot and dry summer can result in additional days with high concentrations.


Note :
Try combining the weather forecasts your class can attempt in Chapter 5 of the Sky Watchers: Guide to Weather with a smog forecast. Activity 6 in the Activities section lists some helpful questions, and answers, along with an answer chart.

Smog Advisories

The Smog Advisory Program, developed in 1993 by Environment Canada, alerts citizens when ground-level ozone concentrations (smog) are expected to exceed the national standard. Smog Advisories are similar to weather warnings, in that they are only issued when conditions are expected to meet specific criteria. In Atlantic Canada, Health Advisories are also issued along with Smog Advisories, recommending that people with sensitivities to pollution consult their physicians. The key difference between Smog Forecasts and Smog Advisories is that the latter are only issued when smog levels threaten to become detrimental to the health of the general population. This occurs when levels are expected to reach the poor category.

What Can We Do To Reduce Pollution?

It is important for the future of our planet, and the health of all living things, that we do what we can to reduce air pollution. Some simple solutions are using a fan instead of air conditioning whenever possible and not letting your car idle unnecessarily. However, by attempting to find alternatives, such as using public transportation or car-pooling, we can lessen our impact on the environment. In the future, it may be that we will be able to utilize other methods to provide us with energy. Solar energy and wind energy are both in use at present and may become more widely used as the technology improves. On the following page, there are some simple tips that you can copy to send home with the students. Encourage them to talk to their parents about trying to work for cleaner air.


Tips: Ask your students to think about all the things they do in a day that contribute to smog formation. Encourage them to keep track of environmentally-friendly choices so they can see the difference they are making.

activity pad and pen

Activity: Ask your students about what can be done to improve the impact we are having on the environment. Have them do research on alternative energy sources such as solar and wind energy.

Tips for Reducing Air Pollution

Many of the choices that we make every day have a direct impact on the amount of pollution that goes into our air from the way we get to work and school in the morning to the way we heat and cool our homes. Since burning fuel is an important part of smog formation, reducing energy use and making wise decisions about the products we use are important steps toward cleaner air. Learn as much as possible about alternative energy sources, and talk about your concerns about smog with other people-including your parents. The following are some simple tips to pass along.

A busGo public.  Use public transportation or car-pool instead of using your car; after all, one bus-load of passengers save nine tonnes of air pollution each year. If smog levels are not too high, try using your bike or walking.
Don't idle your vehicleTurn it off.   Idling your car engine for even one minute uses more fuel than turning it off and re-starting it. Most cars and trucks require only 15 to 30 seconds of idling before being driven, even in winter.
A fuel pumpBe fuel efficient.  Make fuel efficiency a prime factor in your choice of vehicle. Pass on the air conditioning, which burns more gas; buy a smaller vehicle to reduce pollution and save on travel costs; and consider alternatives to gasoline such as propane, natural gas and ethanol.
A bicycleSay good-bye to gas.  Swap gasoline-powered vehicles and other machinery, such as motorboats, motorbikes and gas lawnmowers, for human-powered versions like canoes and sailboats, bicycles, and electric or push lawnmowers.
A car with a plume of exhaust behind itDrive smart.  Differences in driving style can lead to a 20 percent variation in fuel consumption. Driving at moderate speeds and avoiding quick starts and stops uses less fuel.
A man running with a tireStay tuned.  Keeping your car engine tuned and your tires properly inflated increases fuel efficiency.
An electric fanUse air with care.  Save fuel by using air conditioning only when needed for comfort and health. Fans use much less energy.
A bucket of paintSay no to solvents.  The evaporation of solvents found in household cleaners (e.g. mineral spirits) and surface coatings (e.g. oil-based paint) is a major source of pollutants which later form ozone. Use alternative products where possible and dispose of solvent-based products properly.

A homeTight is right. Save fuel by upgrading and maintaining your home heating system, insulation and windows.

Think R-2000. When buying a new house or renovating, make energy-efficient choices. R-2000 homes are better sealed and insulated, and therefore use less energy.

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