Guide to marine weather forecasts

Environment Canada (EC) provides a marine forecasting service to mariners and marine interests. This enables them to make informed decisions about marine weather conditions that may impact their safety, security or operations. EC also provides marine forecasts in order to meet Canada’s treaty obligations under the International Maritime Organization’s Safety Of Life At Sea (SOLAS) Convention.

There are three main marine forecast bulletins issued by EC. In addition to this, descriptive marine synopses are issued by the Department in conjunction with these marine forecast bulletins. The three marine forecast bulletins are each described in further detail in the next section.

On this page

  1. Types of marine forecasts
  2. Forecast issue times and valid periods
  3. Forecast time qualifiers in relation to clock time
  4. What information is included in the marine forecast?
  5. Marine forecasts - sample text bulletins
  6. Marine forecasts - Weather.gc.ca website
  7. Forecast updates - when and why
  8. Major weather elements included in the marine forecasts
  9. Interpreting the wording of a marine forecast
  10. Marine warnings and watches program
  11. Synoptic warnings
  12. Localized warnings and watches
  13. Ice warnings

Types of marine forecasts

Regular marine forecast

The regular marine forecast gives a description of the marine winds and weather, visibility, and/or freezing spray (if applicable), expected over the marine district. It also states any marine warnings or watches that may be in effect.

Extended marine forecast

The extended marine forecast is meant for longer range planning purposes and therefore only gives a description of the marine winds expected over the marine district. Marine wind warnings are not included with the extended marine forecast because of the greater potential for forecast variability in longer range outlooks.  

Wave height forecast

The wave height forecast gives a description of the significant wave heights expected over the marine district.

Marine synopses

The marine synopses consist of two bulletins:

Forecast issue times and valid periods

Regular marine forecast

The regular marine forecast is issued two to four times daily. The number of forecasts and the issue times are determined regionally. The period of coverage is from the forecast issue time out to midnight of the second day of the stated forecast period. Each day of this two-day period is referred to as Day 1 and Day 2 (See Table 1).

Extended marine forecast

The extended marine forecast is issued twice a day, and the issues times are determined regionally. The period of coverage begins after midnight of Day 2 and extends out to midnight of the fifth day of the stated forecast period. Each day of this extended three-day period is referred to as Day 3Day 4, and Day 5 (See Table 1).

Wave height forecast

For waters where wave height forecasts are issued, the wave height forecast is issued two times daily. The issue times are determined regionally, but issue-times are usually the same as, or shortly after, the regular marine forecast issue time. The period of coverage is from the forecast issue time out to midnight of the second day of the stated forecast period. Each day of this two-day period is referred to as Day 1 and Day 2 (See Table 1).

Technical marine synopsis

The technical marine synopsis is issued with the regular marine forecast, and its time period of coverage corresponds to the time period of coverage of the regular marine forecast.

Marine weather statement

A marine weather statement is a non-scheduled bulletin that is issued on an “as needed” basis. It is used in special circumstances to describe the synoptic situation or potentially high impact marine weather expected to occur beyond the period of coverage of the regular marine forecast. This type of marine weather statement is issued at the forecaster’s discretion.

Table 1.  Definition of the periods of coverage associated with the regular forecast (day 1 and day 2) and the extended forecast (day 3, day 4, and day 5)
Forecast terms Corresponding valid time period (local time) Remarks
Today Issuing time to 5:59 p.m.  
Tonight

6:00 p.m. - 5:59 a.m.

or

issue time to 05:59 a.m.

When a forecast is issued after 6:00 p.m., valid time for the phrase Tonight covers from the time of issue to 5:59 a.m. the next day
Day 2 6:00 a.m. - 11:59 p.m. Identified using the name of day
Day 3 12 midnight - 11:59 p.m. Identified using the name of day
Day 4 12 midnight - 11:59 p.m. Identified using the name of day
Day 5 12 midnight - 11:59 p.m. Identified using the name of day

For simplicity, the marine forecast will make use of a limited number of time-qualified phrases such as “diminishing early this afternoon” or “ending tonight” to convey information about when significant changes to the marine weather are expected to occur.

These timing phrases are defined based on (local) clock time. For reference, forecast timing phrases and their associated defined clock times are stated in Table 2 below.

Forecast time qualifiers in relation to clock time

Table 2. Time and sub-time period definitions
Time period term Corresponding time period (local time) Sub-time period term Corresponding time period (local time) 
Morning 6:00 a.m. - 11:59 a.m.

Early morning

Late morning

6:00 a.m. - 08:59 a.m.

9:00 a.m. - 11:59 a.m.

Near noon 11:01 a.m. - 12:59 p.m.    
Afternoon 12 noon - 5:59 p.m.

Early afternoon

Late afternoon

12 noon - 2:59 p.m.

3:00 p.m. - 5:59 p.m.

Late in the day 3:00 p.m. - 11:59 p.m.    
Evening 6:00 p.m. - 11:59 p.m.

Early evening

Late evening

6:00 p.m. - 8:59 p.m.

9:00 p.m. - 11:59 p.m.

Near midnight 11:01 p.m. - 12:59 a.m.    
Overnight 12 midnight - 5:59 a.m.

After midnight

Late overnight

12 midnight - 2:59 a.m.

3:00 a.m. - 5:59 a.m.

What information is included in the marine forecast?

Day 1 and day 2 (regular and wave height forecasts)

The regular marine forecast will contain the following marine weather elements:

The wave height forecast includes the following:

Days 3, 4 and 5 (extended marine forecast)

The extended marine forecast includes the following:

Marine forecasts - sample text bulletins

Regular marine forecast text bulletin

The numbers on the left are provided as a reference to the description of the forecast text associated with that particular section of the forecast bulletin.

  1. FQCN13 CYQX 211330
    Marine forecast for Newfoundland issued by Environment Canada at 10:00 a.m. NST Wednesday 21 January 2009 for today tonight and Thursday.
    The next scheduled forecast will be issued at 3:30 p.m.

  2. Fog implies visibility less than 1 mile.

  3. Strait of Belle Isle.

  4. Gale warning in effect.
    Freezing spray warning in effect.

  5. Wind southwest 15 to 20 knots increasing to northwest 35 early this evening diminishing to 20 Thursday morning. A few flurries beginning this evening. Visibility 1 mile or less in flurries. Over open water freezing spray beginning this evening and ending Thursday morning. Temperature minus 5 falling to minus 15 this evening.

Description

  1. The first line of the title block states the telecommunication header of the marine forecast. The telecommunication header is a World Meteorological Organization (WMO) alphanumeric identifier that indicates the country and regional issuing office, as well as the UTC time and date of issue. The title block then states the regional waters for which the forecast pertains to, then the (local) time and date of issue. The period of coverage the forecast is valid for, and when the next forecast will be issued, are also included.

  2. The visibility-in-fog statement is used to advise mariners that the presence of fog in the marine forecast implies obstruction to visibility that can range from near zero in thick fog to almost 1 nautical mile in patlihy fog. The fog statement also avoids having to mention visibility in fog each time fog is forecast, so the visibility-in-fog statement helps to shorten the marine forecast too.

  3. The geographic name of the marine district is stated for the forecast it applies to.

  4. The warning or watch status statement is included if there are any warnings or watches in effect for the marine district.

  5. The marine forecast text may contain up to four marine weather elements: (1) wind direction and speed, (2) weather conditions and visibility, if applicable, (3) freezing spray, if applicable, and (4) air temperature, if applicable.

Extended marine forecast text bulletin

Wave height forecast text bulletin 

The numbers on the left are provided as a reference to the description of the forecast text associated with that particular section of the forecast bulletin.

  1. FQCN23 CYQX 210930
    Wave height forecast for Newfoundland issued by Environment Canada at 6:00 a.m. NST Wednesday 21 January 2009 for today tonight and Thursday.
    The next scheduled forecast will be issued at 6:00 p.m.

  2. Forecast values are combined wind wave and swell heights.
    Wave heights may vary considerably due to shoreline and depth effects.

  3. Strait of Belle Isle
    Northeast Gulf.

  4. Over open water seas 1 metre building to 1 to 2 Thursday afternoon.

Description:

  1. Title block (including telecommunication header) provides the same level of detail as described for the regular marine forecast bulletin.

  2. An advisory stating that the wave heights expected are based on the combined effect of wind waves generated within the marine district as well as swell waves that may originate from outside the marine district. The advisory also states that the bathymetry of coastal zones may cause considerable variations from the forecast wave heights closer to shore.

  3. The geographic name(s) the marine districts immediately precede the wave height forecast statement.

  4. The wave height forecast statement. Wave height is the only element described. (Note that the term Seas is used to denote waves in ocean water and Waves is used for the Great Lakes.)

Technical marine synopsis text bulletin

The numbers on the left are provided as a reference to the description of the forecast text associated with that particular section of the forecast bulletin.

  1. FQCN10 CWVR 211100
    Technical marine synopsis for the Pacific waters issued by Environment Canada at 4:00 a.m. PDT Thursday 21 May 2009 for today tonight and Friday.
    The next scheduled forecasts will be issued at 10:30 a.m.

  2. Systems position.
    At 4:00 a.m. PDT today ridge located on a line north-south overeastern Queen Charlotte Sound.
    By 5:00 p.m. PDT today ridge located 60 miles west of the Queen Charlotte Islands.

Description:

  1. Title block (including telecommunication header) provides the same level of detail as described for the regular marine forecast bulletin.

  2. The body of the synopsis text begins with the heading “Systems position,” followed by a brief description of the expected movements and trends of the weather systems impacting the marine district. Only significant weather systems are mentioned.

Technical marine synopsis text bulletin

The numbers on the left are provided as a reference to the description of the forecast text associated with that particular section of the forecast bulletin.

  1. FQCN10 CWVR 211100
    Technical marine synopsis for the Pacific waters issued by Environment Canada at 4:00 a.m. PDT Thursday 21 May 2009 for today tonight and Friday.
    The next scheduled forecasts will be issued at 10:30 a.m.<$code>

  2. Systems position.
    At 4:00 a.m. PDT today ridge located on a line north-south overeastern Queen Charlotte Sound.
    By 5:00 p.m. PDT today ridge located 60 miles west of the Queen Charlotte Islands.

Description:

  1. Title block (including telecommunication header) provides the same level of detail as described for the regular marine forecast bulletin.

  2. The body of the synopsis text begins with the heading “Systems position,” followed by a brief description of the expected movements and trends of the weather systems impacting the marine district. Only significant weather systems are mentioned.

Marine weather statement text bulletin

The numbers on the left are provided as a reference to the description of the forecast text associated with that particular section of the forecast bulletin.

  1. FQCN20 CWHX 122000
    Marine weather statement for Nova Scotia issued by Environment Canada at 4:00 p.m. AST Thursday 12 March 2009.

  2. A prolonged period of freezing rain is forecast over coastal sectionlong Eastern Shore and Forchu tonight as temperatures remain steady near zero. The freezing rain may result in hazardous icing on vessels and marine infrastructure.Freezing rain will end overnight or early Friday morning as a milder southerly flow develops over the district and temperatures rise above zero.Mariners are advised to take necessary safety precautions and to monitor Coast Guard marine radio or Weatheradio for updated forecasts or warnings.End

Description:

  1. Title block (including telecommunication header) provides the same level of detail as described for the regular marine forecast bulletin.

  2. The text of the marine weather statement itself; the statement will describe potentially hazardous marine weather, or may provide additional information about marine weather conditions not covered in forecasts or warnings.

Marine forecasts - weather.gc.ca website

The map on Marine forecasts and warning for Canada allows you to select the marine district forecasts.

For more weather information, click on the tabs above the text box once a marine district has been selected.

Forecast updates - when and why

Forecasts are updated as needed when the difference between the forecast and actual conditions are such that the security or safety of mariners is at risk, or when the difference between forecast and actual conditions poses a hindrance to normal marine operations. Updated forecasts will only include the marine areas to which the update applies.

Regular marine forecasts will be updated when one or more of the following criteria are met:

Major weather elements included in the marine forecasts

Wind element

Wind

Included in the forecast for Day 1 and 2?  Yes.
Included in the forecast for Day 3, 4, and 5? Yes.

Days 1 and 2

Wind is a compulsory element in all regular marine forecasts; in the context of the marine forecast, wind is defined as the prevailing or mean wind speed and direction expected at 10 meters above sea level.

The term gusts may be used when the mean wind speed is observed or expected to increase by 10 knots or more for short durations, on the order of seconds. Example: Wind south 25 knots with gusts to 35 along the coast.

Days 3, 4 and 5

Wind is the only element included in the extended marine forecast. Extended marine forecasts will have less detail than the regular marine forecast, with a maximum of three significant changes in wind stated for Day 3, and a maximum of two significant changes stated for Days 4 and 5.

A significant change in observed or forecast winds for Days 1 to 5 is defined with reference to the following criteria:

Weather conditions, precipitation and visibility element

Weather conditions and precipitation, visibility

Included in the forecast for Day 1 and 2?  Yes.
Included in the forecast for Day 3, 4, and 5?  No.

Days 1 and 2

Weather conditions and precipitation are elements that are included in the regular marine forecast. If these elements are expected to reduce visibility to 1 nautical mile or less, this will be stated. Precipitation amounts are never stated.

Freezing spray element

Freezing spray

Included in the forecast for Day 1 and 2?  Yes.
Included in the forecast for Day 3, 4, and 5?  No.

Days 1 and 2

Freezing spray refers to ice build-up on marine infrastructure such as vessel hulls, decks, guy wires, etc that may affect vessel stability or deck operations. The impact of icing due to freezing spray is also dependent on individual vessel characteristics and operating conditions.

A freezing spray warning is issued when ice accretion resulting from freezing spray is expected to reach moderate criteria, defined as ice accretion rates of between 0.7 and 2 centimetres per hour (cm/h); or severe criteria, defined as ice accretion rates exceeding 2 cm/h.

A significant change in freezing spray is defined as the onset or cessation of freezing spray conditions, or when freezing spray intensity changes from moderate to severe, or vice versa.

Air temperature element

Air temperature

Included in the forecast for Day 1 and 2? YesFootnote 1 .
Included in the forecast for Day 3, 4, and 5? No.

Days 1 and 2

Air temperature is expressed in degrees Celsius and it must be mentioned if it is expected to be zero or below zero °C. The temperature is not mentioned if it is expected to remain above the freezing point.

A change in air temperature is considered significant when temperature falls below the freezing point or when there is a change of 5 degrees or more. (Note: A significant change in temperature does not necessitate an update of the regular forecast).

* Note that marine forecasts issued for Ontario Region do not include air temperature.

Interpreting the wording of a marine forecast

As mentioned in Section 1 of this Guide (types of marine forecast), there may be up to four marine weather elements included in regular or updated marine forecasts. At times the marine forecast can become quite lengthy, particularly during the winter storm season as extra wording may be required to convey the meteorological and warning information comprising the marine forecast.

As such, in the interests of brevity and utility for the end-user, the marine forecast will exclude wording that may be redundant, or that does not provide additional information for the end-user.

Since the marine forecast is worded in such a way so as to minimize length, end-users should note that insignificant changes in marine weather elements, such as wind and visibility, are not usually mentioned so as to avoid unnecessary or redundant wording. However, significant changes to marine weather elements are explicitly stated to ensure the forecast information is conveyed.

If the last significant change to the wind forecast occurs on Day 1, the wind statement will not be repeated in the Day 2 wind forecast. To illustrate, refer to wind statement of the following marine forecast:

FQCN13 CWUL 190700
MARINE FORECASTS FOR THE ST. LAWRENCE AND SAGUENAY RIVERS ISSUED BY ENVIRONMENT CANADA AT 3:00 A.M. EDT THURSDAY 19 MARCH 2009 FOR TODAY TONIGHT AND FRIDAY.
THE NEXT SCHEDULED FORECASTS WILL BE ISSUED AT 3:00 P.M.

FOG IMPLIES VISIBILITY LESS THAN 1 MILE.

MONTREAL TO TROIS-RIVIERES.
WIND WEST 15 KNOTS DIMINISHING TO LIGHT EARLY THIS EVENING. HIGH TODAY PLUS 3. LOW TONIGHT MINUS 12. HIGH FRIDAY MINUS 1.

Note that the stated period of coverage for the above forecast is TODAY TONIGHT AND FRIDAY, and that the wind forecast states WIND WEST 15 KNOTS DIMINISHING TO LIGHT EARLY THIS EVENING. Since there is no further mention of changes to the wind after early this (Thursday) evening, this implies that light winds are expected beginning early Thursday evening and persisting through to midnight Friday.

In this case there is no significant change in the wind during the forecast period, and the marine forecast will notrepeat the same wind forecast for subsequent times of the forecast part-periods (this afternoon, tonight, etc). To illustrate, refer to wind statement of the following marine forecast:

FQCN13 CWUL 190700
MARINE FORECASTS FOR THE ST. LAWRENCE AND SAGUENAY RIVERS ISSUED BY ENVIRONMENT CANADA AT 3:00 A.M. EDT THURSDAY 19 MARCH 2009 FOR TODAY TONIGHT AND FRIDAY.
THE NEXT SCHEDULED FORECASTS WILL BE ISSUED AT 3:00 P.M.

FOG IMPLIES VISIBILITY LESS THAN 1 MILE.

MONTREAL TO TROIS-RIVIERES.
WIND WEST 15 KNOTS. HIGH TODAY PLUS 3. LOW TONIGHT MINUS 12. HIGH FRIDAY MINUS 1.

Note that the stated period of coverage for the above forecast is TODAY TONIGHT AND FRIDAY, and that the wind forecast states WIND WEST 15 KNOTS. Since there are no further stated changes, this implies that 15 knot westerlies are expected to persist during the entire forecast period, from 3 AM Thursday morning through to midnight Friday.

Marine Warnings and Watches Program

The Marine Warning and Watches Program provides advisories to mariners or marine interests to inform them of marine weather conditions that may pose a hazard to their safety, security, or operations.

Marine warnings and watches are issued year round, or during the shipping season where forecast waters may close seasonally due to the presence of ice. Marine warnings or watches are issued whenever criteria are met or expected to be met during the valid period of the regular or updated forecast.

Although warnings or watches are not issued for anticipated marine weather events which occur beyond the regular or updated marine forecast time period of coverage, marine weather statements may be issued to provide further detail regarding potentially high impact marine weather events expected to occur during the extended marine forecast time period of coverage.

Marine warnings and watches fall into two main categories: (1) synoptic warnings and (2) localized warnings & watches. Another category of warnings include the ice warnings of which the Canadian Ice Service is the responsible issuing agency.

Synoptic warnings

The term “synoptic warning” in this context means that that the geographic extent over which the warning applies is of larger scale. Synoptic warnings are issued for potentially hazardous marine weather events that affect a significant portion of the marine district, or multiple marine districts.

Synoptic warnings include the following four categories of winds and freezing spray:

Note that synoptic wind warnings apply to the mean wind only. Synoptic wind warnings are not issued for wind gusts that happen to reach warning criteria.

Synoptic warnings appearance in text bulletins

In the text bulletin of the regular or updated marine forecast, synoptic warnings in effect will be stated in a headline immediately after the marine district names(s) to which the warnings apply (refer to section 5 of this Guide).

Synoptic warnings appearance on Weather.gc.ca

On EC’s Weather.gc.ca marine forecast website, synoptic warnings in effect will be highlighted by the red banner immediately below the marine district name(s) to which the warnings apply (refer to section 6 of this Guide).  Clicking on the banners will navigate the webpage user to a criteria description of the synoptic warning in effect.  This information is located under the Warnings Tab on the relevant marine district’s Forecast page.

Localized warnings and watches

The terms “localized warning” and “localized watch” in this context means that the geographic extent to which the localized warning or watch applies is of smaller scale. Localized warnings or watches would be issued for potentially hazardous marine weather events that only affect a localized portion of the marine district.

Localized marine warnings

Localized warnings are issued for the following marine weather events:

Localized marine watches

Localized watches are issued if conditions are favourable for the development of the potentially hazardous marine weather events. The following watches may be issued:

Note that High water level watches are not issued.

Localized warnings/watches appearance in text bulletins

In the text bulletin of the regular or updated marine forecast, localized warnings and watches in effect will be stated in a headline immediately after the marine district name(s) to which the localized warnings or watches apply.

WHCN13 CWNT 051715
Marine warning for the Western Arctic waterway issued by Environment Canada at 2:15 p.m. MDT Monday 5 June 2006.

For immediate broadcast

Squall warning for :
=New= Tuktoyaktuk.

       In effect from 2:15 p.m. to 4:00 p.m.

Squall watch for :
           Baillie.

       In effect from 2:15 p.m. to 8:00 p.m
-----------------------------------------------
Watches/warnings ended

Squall warning ended for :
           Mackenzie.
-----------------------------------------------
==Discussion==
Scattered thunderstorms will accompany a cold front crossing southwestern waters this afternoon. Winds gusting to 35 knots or more are forecast in association with the thunderstorms.

This is a warning that potentially hazardous marine weather is imminent. Mariners are advised to take necessary safety precautions and monitor the forecast for updated warnings.

End

Localized warnings/watches appearance on Weatheroffice

On EC’s Weather.gc.ca marine forecast website, localized warnings in effect will be highlighted by red banners immediately below the marine district name(s) to which the localized marine warnings apply. Localized marine watches will be highlighted by yellow banners immediately below the marine district name(s) to which the localized watch(es) apply.

Clicking on either of these banners will navigate the webpage user to detailed information regarding the localized warning or watch in effect. This information is located under the Warnings Tab on the relevant marine district’s Forecast page.  

Ice warnings

Ice warnings are issued to report hazardous conditions within an ice field. They are included in the Ice Forecast bulletin. Further information regarding the ice forecast program can be obtained from the Canadian Ice Service by visiting their website and reviewing their Ice Products Guide.

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