Public Alerting Criteria

Environment Canada issues alert bulletins for the following weather hazards:

Please note for the following tables “Threshold criteria” is defined as “A set of defined weather or environmental parameters, and their associated values, related to a known hazard that are used as a level marker for the beginning of and ending of a weather or environmental instance of a hazard, for which an alert is normally issued.”

 

Blizzard

Table 1. Alerting parameters Environment Canada uses for issuing a Blizzard Warning
Alert TypeLocationThreshold Criteria
WarningNational, except North of the tree lineWhen winds of 40 km/hr or greater are expected to cause widespread reductions in visibility to 400 metres or less, due to blowing snow, or blowing snow in combination with falling snow, for at least 4 hours.
WarningNorth of the tree lineSame as above, except conditions are expected to last for at least 6 hours.

 

Blowing Snow

Table 2. Alerting parameters Environment Canada uses for issuing Blowing Snow
Alert TypeLocationThreshold Criteria
WarningNational, south of tree lineWhen blowing snow, caused by winds of at least 30 km/h, is expected to reduce visibility to 800 metres or less for at least 3 hours.

Dust Storm

Table 3. Alerting parameters Environment Canada uses for issuing a Dust Storm
Alert TypeLocationThreshold Criteria
WarningAlberta, Saskatchewan and Manitoba (ONLY)When blowing dust is expected to occur, reducing visibility to 800 metres or less for one hour or more.

 

Flash Freeze

Table 4. Alerting parameters Environment Canada uses for issuing a Flash Freeze
Alert TypeLocationThreshold Criteria
WarningNational, except extreme Northern Quebec*When significant ice is expected to form on roads, sidewalks or other surfaces over much of a region because of the freezing of residual water from either melted snow, or falling/fallen rain due to a rapid drop in temperatures.

*No alert of this type exists for this region at this moment.

 

Freezing Drizzle

Table 5. Alerting Parameters Environment Canada uses for issuing a Freezing Drizzle Warning
Alert TypeLocationThreshold Criteria
WarningNational, except extreme Northern Quebec*When a period of freezing drizzle is expected for at least 8 hours.

*No alert of this type exists for this region at this moment.

Freezing Rain

Table 6. Alerting Parameters Environment Canada uses for issuing a Freezing Rain Warning
Alert TypeLocationThreshold Criteria
WarningBritish Columbia, Yukon, Alberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Ontario and Quebec (except extreme Northern Quebec*)When freezing rain is expected to pose a hazard to transportation or property;
or
When freezing rain is expected for at least 2 hours.
WarningNova Scotia, New Brunswick, Prince Edward Island, Magdalen Islands , Newfoundland and LabradorWhen freezing rain is expected to pose a hazard to transportation or property;
or
When freezing rain is expected for at least 4 hours.

*No alert of this type exists for this region at this moment.

Frost

Table 7. Alerting Parameters Environment Canada uses for issuing a Frost Warning
Alert TypeLocationThreshold Criteria
WarningSouthern portions of Canada except British Columbia*Issued during the growing season when widespread frost formation is expected over an extensive area. Surface temperatures are expected to fall near freezing in the overnight period.

*No alert of this type exists for this region at this moment.

High Heat and Humidity

Table 8. Alerting Parameters Environment Canada uses for issuing a
High Heat and Humidity Warning
Alert TypeLocationThreshold Criteria
WarningQuebecIssued when the humidex value is 40 or greater and when the temperature is 30°C or warmer, and both conditions persist for at least one hour. The Quebec Ministry of Health is a co-partner in this program.

Humidex

Table 9. Alerting Parameters Environment Canada uses for issuing a
Humidex Statement /Advisory
Alert TypeLocationThreshold Criteria
Statement AdvisoryAlberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Ontario, Nova Scotia, and New BrunswickIssued when the heat and humidity conditions exceed local criteria values.

 

Hurricane

Table 10. Alerting Parameters Environment Canada uses for issuing a
Hurricane Watch and/or Warning
Alert TypeLocationThreshold Criteria
WatchNational, including all coastal and inland regionsWhen, within the following 36 hours, a hurricane or a developing hurricane is expected to pose a possible threat, with the risk of hurricane force winds (sustained gales of 118 km/h or higher) threatening the area.
WarningNational, including all coastal and inland regionsWhen hurricane-force gales (average sustained winds of 118 km/h or higher) caused by a hurricane, or a strong tropical storm that may strengthen to hurricane force before making landfall, are expected to occur in 24 hours or less.  It may also include areas where storm surge or exceptionally high waves are expected, even though winds may be less than hurricane force.

Rainfall

Table 11. Alerting parameters for Short Duration Rainfall Events (Heavy Downpour)
Alert TypeLocationThreshold Criteria
WarningAlberta, Saskatchewan, Manitoba, Ontario, and Quebec (except extreme Northern Quebec*)When 50 mm or more of rain is expected within one hour.
WarningBritish Columbia, Yukon, Northwest Territories, Nunavut, New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and LabradorWhen 25 mm or more of rain is expected within one hour.

 

Table 12. Alerting parameters Environment Canada uses for issuing a
Rainfall Warning in the Summer
Alert TypeLocationThreshold Criteria
WarningNational, except extreme Northern Quebec* and portions of British Columbia, as specified belowWhen 50 mm or more of rain is expected within 24 hours;
or
When 75 mm or more of rain is expected within 48 hours.
WarningInland Vancouver Island,  West Vancouver Island, North Vancouver Island, Central Coast – coastal sections, and North Coast – coastal sectionsWhen 100 mm or more of rain is expected within 24 hours.

 

Table 13. Alerting parameters Environment Canada uses for issuing a
Rainfall Warning in the Winter
Alert TypeLocationThreshold Criteria
WarningNational, except extreme Northern Quebec* and British ColumbiaWhen 25 mm or more of rain is expected within 24 hours.
WarningBritish Columbia, exceptWhen 50 mm or more of rain is expected within 24 hours;
or
When 75 mm or more of rain is expected within 48 hours.
WarningInland Vancouver Island,  West Vancouver Island, North Vancouver Island, Central Coast – coastal sections, and North Coast – coastal sectionsWhen 100 mm or more of rain is expected within 24 hours.

 

Table 14. Alerting parameters Environment Canada uses during a thaw only
Alert TypeLocationThreshold Criteria
WarningInterior British Columbia, Fort Nelson, Muncho Lake Park - Stone Mountain Park, Dease Lake, Cassiar Mountains, and AtlinWhen 25 mm or more of rain is expected to within 24 hours.

*No alert of this type exists for this region at this moment.

Severe Thunderstorm

Table 15. Alerting parameters Environment Canada uses for issuing a
Severe Thunderstorm Watch and/or Warning
Alert TypeLocationThreshold Criteria
WatchNational, except extreme Northern Quebec*
When conditions are favourable for the development of severe thunderstorms with one or more of the following conditions:
  • Wind gusts of 90 km/h or greater, which could cause structural wind damage;
  • Hail of two centimeters (cm) or larger in diameter; or
  • Heavy rainfall, as per rainfall criteria, excluding those for winter and during thaw (see above).
WarningNational, except extreme Northern Quebec*
When there is evidence based on radar, satellite pictures, or from a reliable spotter that any one or more of the following three weather conditions is imminent or occurring:
  • Wind gusts of 90 km/h or greater, which could cause structural wind damage;
  • Hail of two centimeters (cm) or larger in diameter; or
  • Heavy rainfall, as per rainfall criteria, excluding those for winter and during thaw (see above).

*No alert of this type exists for this region at this moment.

 

Snowfall

Table 16. Alerting parameters Environment Canada uses for issuing a Snowfall Warning
Alert TypeLocationThreshold Criteria
Warning
Newfoundland and Labrador, New Brunswick, Nova Scotia, Prince Edward Island, Magdalen Islands , Quebec (except extreme Northern Quebec*) , Ontario and British Columbia, including:

Whistler, Howe Sound, Inland Vancouver Island, North Columbia, West Columbia, Kinbasket, Elk Valley, Yoho Park - Kootenay Park, and North Coast - Inland Sections Regions
When 15 cm or more of snow falls within 12 hours or less.
WarningAlberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Yukon, British Columbia -all regions not specified elsewhereWhen 10 cm or more of snow falls within 12 hours or less.
WarningBritish Columbia: Southern and Central Coast – coastal sectionsWhen 10 cm or more of snow falls within 12 hours or less;
or
When 5 cm or more of snow falls within 6 hours or less.
WarningHaines Skagway roads, YukonWhen 20 cm or more of snow falls within 24 hours or less.

*No alert of this type exists for this region at this moment.

Snow Squall

Table 17. Alerting parameters Environment Canada uses for issuing a
Snow Squall Watch and/or Warning
Alert TypeLocationThreshold Criteria
WatchNational, except extreme Northern Quebec*
When conditions are favourable for the development of open water snow squall down wind of large bodies of water, like the Great Lakes, with one or more of the following conditions:
  • Localized, intense snowfall producing snowfall amounts of 15 cm or more in 12 hours or less.
  • Reduced visibility (less than 400 metres) caused by heavy snow with or without blowing snow for 3 hours or more.

Note that local snow accumulations may be significant.

 

Table 18. Alerting parameters Environment Canada uses for issuing a
Snow Squall Watch and/or Warning in Open-Water
Alert TypeLocationThreshold Criteria
WarningLocationThreshold Criteria
WarningNational, except extreme Northern Quebec*
When, down wind of large bodies of water, like the Great Lakes, snow squalls are imminent or occurring with one or more of the following conditions being produced:
  • Localized, intense snowfall producing snowfall amounts of 15 cm or more in 12 hours or less.
  • Reduced visibility (less than 400 metres) caused by heavy snow with or without blowing snow for 3 hours or more.
Note that local snow accumulations may be significant.

 

Table 19. Alerting parameters Environment Canada uses for issuing a
Snow Squall Watch and/or Warning in a Front
Alert TypeLocationThreshold Criteria
WarningNational, except extreme Northern Quebec*When there is a brief period (less than one hour) of very poor visibility (400 metres or less), caused by heavy snow and blowing snow, and accompanied by strong, gusty winds of 45 km/hr or greater, is expected to occur with the passage of a cold front.

*No alert of this type exists for this region at this moment.

Storm Surge

Table 20. Alerting parameters Environment Canada uses for issuing a Storm Surge Warning
Alert TypeLocationThreshold Criteria
WarningNova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, Gulf of Saint Lawrence coastal areas and the Magdalen Islands (ONLY)Issued for abnormally high water levels and high waves (storm surge or storm tide) caused by storms, which have the potential to cause coastal flooding. This usually occurs when astronomical tides are at their maximum.

 

Tornado

Table 21. Alerting parameters Environment Canada uses for issuing a
Tornado Watch and/or Warning
Alert TypeLocationThreshold Criteria
WatchNational, except extreme Northern Quebec*When conditions are favourable for the development of severe thunderstorms with one or more tornadoes.
WarningNational, except extreme Northern Quebec*When a tornado has been reported; or when there is evidence based on radar, or from a reliable spotter that a tornado is imminent.

*No alert of this type exists for this region at this moment.

 

Tropical Storm

Table 22. Alerting parameters Environment Canada uses for issuing a
Tropical Storm Watch and/or Warning
Alert TypeLocationThreshold Criteria
WarningNational, including all coastal and inland regions
When, within the following 36 hours, a tropical storm or a developing tropical storm is expected to pose a possible threat, with the risk of tropical-storm force winds (sustained gales of 63-117 km/h) threatening the area. This watch could be issued for:
  • A tropical storm; or
  • A hurricane that might approach an area but be far enough away that it is expected to bring gales that are less than hurricane force (118 km/h or higher).
WarningNational, including all coastal and inland regionsWhen coastal and/or coastal winds of 63 to 117 km/h caused by a tropical cyclone are expected to occur.

Tsunami

Table 23. Alerting parameters Environment Canada uses for issuing a Tsunami Warning
Alert TypeLocationThreshold Criteria
WarningEast Coast : Coastal areas of Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, Gulf of Saint Lawrence coastal areas, the Magdalen Islands

West Coast : Coastal areas of British Columbia
For a potential tsunami with significant widespread effects, that is either imminent or expected. Advisories are also issued for a threat of a potential tsunami that may produce strong currents or waves dangerous to those in or near the water.  

Note: Tsunami warnings are issued in partnership with provincial and federal organizations.

 

Weather

Table 24. Alerting parameters Environment Canada uses for issuing a Weather Warning
Alert TypeLocationThreshold Criteria
WarningNational, except extreme Northern Quebec*A generic weather warning may be issued for extreme weather events for which there is no suitable warning type, because they rarely occur. For example: a major fog event.

A generic weather warning may also be issued for other weather events during situations where the environment is vulnerable due to pre-existing conditions and any further weather could result in a significant hazard. For example:
50 km/h winds following an ice storm which could cause structural wind damage.

A generic weather warning may also be issued for situations where the event is not expected to reach warning criteria values, but there is a special reason for the warning. For example: the first event of the season, or an off-season event.

*No alert of this type exists for this region at this moment.

Wind

Table 25. Alerting parameters Environment Canada uses for issuing a Wind Warning
Alert TypeLocationThreshold Criteria
WarningNational
Including:

Les Suêtes (The warning covers only the coast of the “INVERNESS COUNTY - MABOU AND NORTH” forecast region in Nova Scotia)
70 km/h or more sustained wind;
and/or
Gusts to 90 km/h or more.
WarningExcept:
Alberta

Crowsnest Pass - Pincher Creek - Waterton Lakes Nat. Park
Cardston - Fort Macleod – Magrath
City of Lethbridge;

Newfoundland and Labrador, including:
Wreckhouse Winds (The warning covers only the Wreckhouse area of the West Coast of Newfoundland)

Yukon
Dempster

British Columbia
Western Vancouver Island
80 km/h or more sustained wind;
and/or
Gusts to 100 km/h or more.
WarningExcept:
British Columbia

North Vancouver Island
Central Coast - coastal sections
North Coast - coastal sections
Queen Charlottes
90 km/h or more sustained wind;
and/or
Gusts to 110 km/h or more.

 

Wind Chill

Table 26. Alerting parameters Environment Canada uses for issuing a Wind Chill Warning
Alert TypeLocationThreshold Criteria
WarningNationalIssued to warn of conditions that will cause frostbite to exposed skin. Criteria vary across the country, ranging from wind chill values of -55 in some Arctic regions to -30 in Southwestern Ontario.

Winter Storm**

Table 27. Alerting parameters Environment Canada uses for issuing a
Winter Watch and/or Warning
Alert TypeLocationThreshold Criteria
WatchNational, except extreme Northern Quebec*
When conditions are favourable for the development of severe and potentially dangerous winter weather, including:
  • A blizzard;
  • A major snowfall (25 cm or more within a 24 hour period); and
  • A significant snowfall (snowfall warning criteria amounts) combined with other winter weather hazard types such as: freezing rain, rainfall (over coastal BC only), strong winds, blowing snow and/or extreme wind chill.
WarningNational, except extreme Northern Quebec*
When severe and potentially dangerous winter weather conditions are expected, including:
  • A major snowfall (25 cm or more within a 24 hour period); and
  • A significant snowfall (snowfall warning criteria amounts) combined with other cold weather precipitation types such as: freezing rain, strong winds, blowing snow and/or extreme wind chill.
Blizzard conditions may be part of an intense winter storm, in which case a blizzard warning is issued instead of a winter storm warning.

*No alert of this type exists for this region at this moment.
**Winter storm conditions are not necessarily restricted to the winter season, and may occur in the late autumn and early spring, as well.

Appendix A - Map of the Treeline in Canada

A map of Canada on which the green highlighted area represent the coverage of trees. All regions of Canada can support the growth of trees except in the extreme northern areas of the Yukon, Northwest Territories, Nunavut, Northern Quebec, and Labrador where the influences from the Arctic Circle and Hudson Bay move the treeline southward. This area of no growth creates an "U" shaped area on the map.

Map of the Treeline in Canada