Public weather forecast bulletins

There are two types of public weather forecast bulletins: the regular forecast bulletin, and the extended forecast bulletin.

The regular public forecast bulletin provides a description of the most significant weather conditions expected within the next two days (refer to Table 1 for exact time periods).

The extended forecast bulletin provides a description of the anticipated weather conditions beyond the time period covered by the regular public forecast bulletin: days three to seven. This extended forecast (also referred to as the long range forecast) is more general than the regular forecast.

• Issuing time of forecasts
• Time period covered by forecasts
• Determination of forecast regions
• Forecast time period terminology
• What information is included in the forecast?
• Sample forecast
  • Sample regular forecast (text bulletin)
  • Sample extended forecast (text bulletin)
• Forecast Revision
• Hourly Forecasts

Issuing time of forecasts

Although there are some regional differences, the regular and extended public forecast bulletins are most commonly issued three times a day, at 5:00 a.m., 11:00 a.m., and 4:00 p.m. local time. Issue times of a few bulletins are different from the national standard due to time zone differences within a region.

Time period covered by forecasts

The following table indicates the time period that the forecast covers for each of the three above-mentioned forecast issue times.

Table 1. Time periods for the public forecast bulletin

Below, the same information can be seen along a timeline:

5:00 a.m. forecast issue

The timeline starts with the Today period, which covers the times of 5:00 a.m. to 6:00 p.m. It moves on to the Tonight period, which covers the times of 6:00 p.m. to 6:00 a.m. It then goes into the Tomorrow period, which covers the times of 6:00 a.m. to 6:00 p.m. Lastly, the timeline includes the Nights from Two to Six and the Days from Three to Seven.  Nights are from 6:00 p.m. to 6:00 a.m and Days are from 6:00 a.m. to 6:00 p.m.

11:00 a.m. forecast issue

The timeline starts with the Today period, which covers the times of 11:00 a.m. to 6:00 p.m. It moves on to the Tonight period, which covers the times of 6:00 p.m. to 6:00 a.m. It then goes into the Tomorrow period, which covers the times of 6:00 a.m. to 6:00 p.m. Lastly, the timeline includes the Nights from Two to Six and the Days from Three to Seven.  Nights are from 6:00 p.m. to 6:00 a.m and Days are from 6:00 a.m. to 6:00 p.m.

4:00 p.m. forecast issue:

The timeline starts with the Tonight period, which covers the times of 4:00 p.m. to 6:00 a.m. It moves on to the Tomorrow period, which covers the times of 6:00 a.m. to 6:00 p.m. It then goes into the Tomorrow night period, which covers the times of 6:00 p.m. to 6:00 a.m. Lastly, the timeline includes the Days from Three to Seven and Nights from Three to Six.  Nights are from 6:00 p.m. to 6:00 a.m and Days are from 6:00 a.m. to 6:00 p.m.

Determination of forecast regions

Forecast regions are closely aligned with cities, communities and municipal boundaries. Local factors such as terrain, climatology, land cover and population patterns were used to define these regions. The names of the forecast regions generally correspond with those of the most prominent communities or the geographic regions. All official place names can be found in the Canadian Geographical Names Database.

Forecast time period terminology

Table 2. Terms for Day One and Day Two

What information is included in the forecast?

Days One & Two

The regular public forecast bulletin will always contain the following standard weather elements: (see the Weather Elements and when they are included in the forecast, for further details)

• Sky condition / Precipitation (including type)
• Maximum temperature
• Minimum temperature

The following additional weather elements may also be included, provided certain criteria are met (see the Weather Elements and when they are included in the forecast for these criteria):

• Chance of Precipitation (COP)
• Precipitation amount
• Combinational events (e.g. blizzard)
• Wind
• Obstructions to Visibility (e.g.fog)
• Weather events (e.g. thunderstorm)
• Thermal indices (Wind chill, Humidex)
• Ultraviolet Index (UVI)

Days and Nights Three to Seven

The extended public forecast bulletin will always contain the following standard weather elements (see the Weather Elements and when they are included in the forecast, for further details).

• Sky condition / Precipitation  (including type)
• Minimum temperature
• Maximum temperature
• *Normals for the period

The following additional weather elements may also be included, provided certain criteria are met (see the Weather Elements and when they are included in the forecast for these criteria):

• Chance of precipitation (COP)
• Combinational events (e.g. blizzard)
• Wind
• Obstructions to visibility (e.g.fog)
• Weather events (e.g. thunderstorm)

*Note: The normal temperatures for this period are the climatic normal temperatures for the grouping of regions indicated in the forecast. It is the Day Five normal temperature that is displayed in the extended bulletin. The normal temperatures can change as the grouping of regions in the forecast is changed.

The climatic normal temperatures are derived from 30-year averages of daily highs and lows.

Sample forecast

SAMPLE forecast #1 from the Canada.ca/weather

1. The Forecast Quick Link lets you easily browse through each city to find your local weather forecast.
   
2. The watch/warning/advisory banner will warn you of all latest weather watches, warnings and advisories in effect for your location.  Clicking on the banner will open the full details of the message.
   
3. The links provide quick access to the location's past 24 hour conditions, weather radar, satellite and lightning.
   
4. The Current Conditions box displays all available weather information for the location chosen, along with the time and date that the information is valid.
   
5. The links provide quick access to the hourly forecast, air quality, alerts and jet stream.
   
6. Forecast Icons give a quick, visual description of what the forecast is for the next 7 days and 6 nights. The icons will show the sky conditions, precipitation including Chance of Precipitation (COP), visibility restrictions (fog, blowing snow) and high and low temperatures for the days and nights. Also included is a short worded forecast.
   
7. The Forecast Text is the complete forecast and gives more information than the quick look table. For the first three forecast periods, in addition to the information given in the icons, the text is more descriptive and gives Feels like temperatures (wind chill and Humidex), precipitation amounts as well as start and end time of precipitation, UV Index, wind speed and direction. For the remaining forecast periods, very windy conditions can be forecast.

Sample regular forecast (text bulletin)

1. This text is called the “title block”. It indicates the forecast geographic area, the issue date & and the time for which the of the forecast is and the periods for which the forecast is valid. It also indicates when the next forecast will be issued.  (same for the extended forecast 1.)
2. The forecast region name(s) is the full name of the region(s) or metropolitan area(s) for which the forecast is issued.
3. The forecast text is broken into distinct periods (i.e. today, tonight, tomorrow) for ease of readability. See section 1.2 to learn more about the hours associated with the different time periods.

Sample extended forecast (text bulletin)

1. This text is called the “title block”. It indicates the forecast area, the date and the time for which the forecast is. It also indicates when the next forecast will be issued.
2. The forecast region name(s) is the full name of the region(s) or metropolitan area(s) for which the forecast is issued.
3. The extended forecast bulletin covers day 3 to day 7.

Forecast Revision

Forecasts are revised when the difference between the forecast and actual conditions are such that public security and safety are at risk and/or when inconvenience to the public is thought to be extensive. A revision to the regular public forecast bulletin is initiated when one or more of the following criteria have been satisfied:

• The non-occurrence of forecast precipitation or hazards (freezing rain, definite forecast of thunderstorms, etc.) and vice versa.
• A difference in precipitation type (snow as opposed to rain/freezing rain and vice versa).
• A significant change in the timing of forecast event(s).
• A marked change in temperature regime is expected but is not occurring and vice versa.
• When, to the opinion of the supervisor on duty, the latest forecast does not reflect what is actually occurring and what is expected to occur in the next few hours.

The extended forecast is rarely revised, however if it is revised, one or more of the same criteria above would have to be met to warrant the change(s).

Hourly Forecasts

Environment and Climate Change Canada provides a 24 Hour Forecast link in the upper right hand corner of the Forecast section. If you click on the link it will lead you to the weather forecast information for the next 24 hours. The hourly forecast information appears in a table and shows more detail than our text forecasts.

The table will be updated on an hourly basis, and will always provide 24 hours of information, starting with the next hour.

Sample - 24 Hour Forecast

What is included in the 24 Hour Forecast?

The information displayed will consist of the following weather elements:

• Temperature: a value representing the temperature for the following hour.
• Weather conditions: an image and short summary text representing the most probable weather in the following hour.
• Likelihood of Precipitation (LOP): the chance of precipitation in the following hour.
• UV index: a value representing the intensity of ultraviolet radiation from the sun for the following hours, based on the UV index scale from 0 (minimal risk) to 11+ (extreme risk). If there are no UV index values to display for the entire 24 hour period (night time) the statement ''value not significant" will be displayed.
• Wind: wind speed and direction for the following hour. If there are gusts in the forecast, this information will also be displayed. The letters VR indicate a variable wind direction during the hour.
• Wind chill: the wind chill for the following hour. If there are no wind chill values to display for the entire 24 hour period, this column will not appear. Further information on wind chill can be found at the following link: Learn more about Wind Chill.
• Humidex: the Humidex for the following hour. If there are no Humidex values to display for the entire 24 hour period, this column will not appear. Further information on Humidex can be found here: Learn more about Humidex.

Similar to the city pages, alert banners will display at the top of the page if an alert is in effect.