Backgrounder Information

This section offers a listing of backgrounders providing supplementary information on various Weather and Meteorology services.


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Severe Weather Forecasts

Canada’s weather is full of contrasts with its hot summers and cold, snowy winters, and with these seasons comes dangerous weather conditions. Helping Canadians protect themselves, their families and their property from the hazards of severe weather is an important part of Environment Canada’s (EC) mandate. In fact, EC is the nation’s official source for: weather watches; warnings; advisories; special weather and information statements.

Severe weather conditions include:

  • hurricanes
  • severe thunderstorms
  • flooding
  • extreme cold
  • extreme heat
  • heavy rain and snow
  • hail
  • snow squalls
  • blizzards
  • tornados

EC also runs the Canadian Hurricane Centre in Dartmouth, Nova Scotia, which provides meteorological information on hurricanes, tropical storms and post-tropical storms to help Canadians make informed decisions of how to protect themselves and their property.

EC issues weather watches when conditions are favourable for the development of a weather or environmental hazard that poses a significant threat to public safety and property, but when the occurrence, location, and/or timing of the expected condition(s) is still too uncertain to issue a warning.

EC issues weather warnings when a hazardous weather or environmental event that poses a significant threat to public safety and property is certain or imminent.

EC provides expert advice to emergency management authorities to mitigate emergency situations when weather conditions are important factors.

Severe weather analyses and forecasting

EC meteorologists produce severe weather warnings and forecasts for Canadians 24/7.

Forecasting severe weather begins with an examination of real-time weather data. This leads to an analysis of which atmospheric processes are occurring, and ends with a prediction of the severe weather events that could occur.

All bulletins, forecasts and warnings are produced with the aid of a great deal of technology including:

  • EC’s supercomputer
  • Satellites
  • Doppler radar
  • wind profilers
  • ground weather stations
  • weather balloon data
  • lightning detection

How do weather warnings reach the public?

 When severe weather is on its way, EC takes its role as the official warning provider very seriously. Each year EC issues on average 15,000 severe weather warnings, watches and information statements via:

  • Environment Canada’s Weatheradio system, which continually broadcasts on VHF radio frequencies;
  • Online at Environment Canada’s Meteorological Service website;
  • By phone through the local automated telephone recordings;
  • User-pay phone 1-900 / 1-888 service that enables callers to access meteorologists from 5 am to 6 pm daily;
  • RSS weather and weather warning feeds; 
  • Media outlets across the country

The media is one of EC’s primary means of reaching Canadians about severe weather. The media generally obtain information through their local wire services or through EC’s internet media portal.  The media are vital to ensuring that Canadians receive weather information and alerts in a timely manner.

For more information on the science behind severe weather forecasting, visit the following links:

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One-to-Seven-Day Weather Forecasts

With such a vast country full of defining seasons, it is no wonder that Canadians are often known for being weather obsessed. This is also likely why Environment Canada’s (EC) main forecasting website, receives an average of 50 million visits a month, making it one of the most popular websites in Canada. Despite the relative ease with which we access weather information, the science behind EC’s popular one-to-seven-day weather forecasts is more complex.

Weather forecasters use science and technology to predict the state of the atmosphere at a future time for a given location.
A daily weather forecast provides:

  • Weather alerts, if in effect
  • Temperature
  • Precipitation, including type, probability of and amounts
  • Wind, including speed and direction
  • Fog and other obstructions to visibility
  • Wind chill and Humidex, if appropriate
  • UV Index
  • Air Quality Health Index (for certain communities across the country)

In a seven-day forecast, forecasts for the first two days are expressed as a relatively detailed sequence of expected weather events. Days three to seven are usually listed in a more general sense, focusing on the most significant expected weather for each day.

Environment Canada’s Meteorological Service of Canada plays a very important role in providing the country with its weather forecasts and is the official provider of Canada’s weather alerts (warnings, watches, advisories and special weather statements).

Severe weather warnings, watches and special weather statements alert Canadians to current or expected weather conditions that could impact their safety and their property. It is EC’s goal to ensure that all Canadians know about potential severe weather impacts well in advance.

How are weather forecasts made?

EC’s weather forecasts and alerts are produced using technology, including satellites, Doppler radars, a powerful supercomputer, new forecaster workstations and a greater use of weather information received from the general public.

  • Step 1:
    • The first step in forecasting the weather involves an analysis of the state of the atmosphere. EC collects data daily from thousands of weather monitoring sites across the country and the world.
  • Step 2:
    • All the data collected are analyzed and used in EC’s numerical weather prediction models. These models are essentially the mathematical representations of what is present in the atmosphere. This process is done through the use of EC’s supercomputer.
  • Step 3:
    • Current observations and the numerical model output are used by meteorologists in the analysis and diagnosis of current weather conditions. The meteorologists pay special attention to possible severe weather in the upcoming two days, and will issue severe weather alerts as appropriate. Forecasts are disseminated out to Canadians through EC’s Weather website, Weatheradio, automated telephone answering devices, to the media and for display on numerous weather websites in Canada.

For more information on the science behind weather forecasting, and EC’s one-to-seven-day forecasts visit:

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Monthly and Seasonal Weather Outlooks

Canadians love their weather, which is why Environment Canada (EC) is dedicated to providing Canadians with daily weather forecasts and weather alerts that are often issued alongside them.  However, there is also a benefit in knowing what the weather may be like in the future, which is why EC produces both Monthly and Seasonal Weather Outlooks.

  • Monthly Weather Outlooks are issued on the 1st and 15th day of each month, for temperature only.  
  • Seasonal Weather Outlooks are issued on the 1st day of each month, for temperature and precipitation. A season is three months long.  

These monthly and seasonal outlooks are not meant to describe a sequence of specific weather events, nor to give details about upcoming weather, but are useful because they provide advance notice of possible long range weather conditions.  Monthly and seasonal weather outlooks are of particular interest to weather-sensitive sectors such as agriculture, construction, transportation, forestry, tourism, hydro-electricity generation and to various provincial and federal agencies. 

How are monthly and seasonal outlooks produced?

In December 2011, the Canadian Meteorological Centre (CMC) began running a newly developed Canadian global coupled (one-tier) multi-seasonal prediction system, called the Canadian Seasonal and Interannual Prediction System (CanSIPS), for forecasting monthly to multi-seasonal climate conditions.

CanSIPS is a multi-model ensemble system based on two climate models developed by the Canadian Centre for Climate Modeling and Analysis in Victoria, B.C.  It is a fully coupled atmosphere-ocean-ice-land prediction system, integrated into the CMC operational prediction suite and relies on CMC data assimilation infrastructure.

Deterministic and Probabilistic Forecasts

Before 2013, EC produced only deterministic monthly and seasonal forecasts.  A deterministic forecast is one that gives only one description (example: tomorrow at 1:15 p.m. the temperature will be 3.2 degrees Celsius, and it will begin to rain five minutes later at 1:20 p.m.).

To produce a deterministic forecast, the results from CanSIPS models are averaged and compared to past climatology (currently covering the years 1981 to 2010) to create the temperature and precipitation outlooks.

The monthly deterministic outlook shows three forecast categories, color coded to indicate if the temperature will be:

  • below normal* values in blue;
  • above normal values in red;
  • near normal in white.

For examples of temperature and precipitation probabilistic forecasts, visit the website.

Since 2013, EC also produces probabilistic forecasts (with probability expressed in percent), which is considered a better approach when it comes to monthly and seasonal forecasts.  A probabilistic forecast would say “tomorrow, there is an 85% probability that the temperature will be 3 degrees Celsius or higher at 1:15 p.m., and a 65% probability that rain will have begun by 1:20 p.m.”.

To produce a probabilistic forecast, ten simulations from each model are produced, creating an ensemble of 20 predictions used to calculate probability distributions.  If all of the predictions have similar results, the probability and the confidence level of the outlook is higher.  The more the results differ from each other, the lower the probability and confidence level.

*Note: Presently the monthly weather outlook is a deterministic forecast and is available for temperature only on the website.  EC is currently working at designing a probabilistic monthly weather outlook which will use the Global Ensemble Prediction System, making it more precise and reliable.

For examples of temperature and precipitation deterministic forecasts, visit the website.

At a glance, you can see by region which category- above, near or below normal- is the most probable and the probability that this forecast will come true. 

For more information on the science behind weather forecasting, visit the following links:

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