Criteria for public weather alerts

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.”

Arctic Outflow

Table 1. Alerting parameters Environment Canada uses for issuing an Arctic Outflow Warning
Alert Type Location Threshold Criteria
Warning Coastal British Columbia regions only Any combination of wind speed and temperature giving a wind chill of -20 or lower for 6 hours or more. A separate Wind Warning is not required.

Blizzard

Table 2. Alerting parameters Environment Canada uses for issuing a Blizzard Warning
Alert Type Location Threshold Criteria
Warning National, except North of the tree line When 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.
Warning North of the tree line Same as above, except conditions are expected to last for at least 6 hours.

Blowing Snow

Table 3. Alerting parameters Environment Canada uses for issuing a Blowing Snow Advisory
Alert Type Location Threshold Criteria
Advisory National, south of tree line When 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 4. Alerting parameters Environment Canada uses for issuing a Dust Storm Warning
Alert Type Location Threshold Criteria
Warning Alberta, Saskatchewan and Manitoba (ONLY) When blowing dust is expected to occur, reducing visibility to 800 metres or less for one hour or more.

Extreme Cold

Table 5. Alerting parameters Environment Canada uses for issuing an Extreme Cold Warning
Alert Type Location Threshold Criteria
Warning South-central and Southwestern Ontario Issued when the temperature or wind chill is expected to reach minus 30°C for at least two hours.
Warning Southeastern Ontario, Southern Interior and Coastal B.C., Atlantic Canada except Labrador Issued when the temperature or wind chill is expected to reach minus 35°C for at least two hours.
Warning Western, Central and Eastern Quebec Issued when the temperature or wind chill is expected to reach minus 38°C for at least two hours.
Warning Central Interior B.C., Northern Ontario, Prairies - Alberta, Southern Saskatchewan, Southern Manitoba Issued when the temperature or wind chill is expected to reach minus 40°C for at least two hours.
Warning Far Northern Ontario, northern Saskatchewan, northern Manitoba, Northern B.C., Labrador Issued when the temperature or wind chill is expected to reach minus 45°C for at least two hours.
Warning Northern Quebec Issued when the temperature or wind chill is expected to reach minus 48°C for at least two hours.
Warning Yukon, NWT (except Paulatuk, Sachs Harbour and Ulukhaktok), Baffin Island (except Igloolik and Hall Beach), extreme northeast Manitoba Issued when the temperature or wind chill is expected to reach minus 50°C for at least two hours.
Warning Nunavik Issued when the temperature or wind chill is expected to reach minus 52°C for at least two hours.
Warning NWT (Paulatuk, Sachs Harbour and Ulukhaktok only), Baffin Island (Igloolik and Hall beach only) Western and Northern Nunavut Issued when the temperature or wind chill is expected to reach minus 55°C for at least two hours.

Flash Freeze

Table 6. Alerting parameters Environment Canada uses for issuing a Flash Freeze Warning
Alert Type Location Threshold Criteria
Warning National, except Nunavik* 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.

Fog

Table 7. Alerting parameters Environment Canada uses for issuing a Fog Advisory
Alert Type Location Threshold Criteria
Advisory Newfoundland and Labrador, New Brunswick, Nova Scotia and Prince Edward Island When low visibilities in fog are expected for at least 18 hours.
Advisory Elsewhere National, except Nunavik* When low visibilities in fog are expected for at least six hours.

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

Freezing Drizzle

Table 8. Alerting Parameters Environment Canada uses for issuing a Freezing Drizzle Advisory
Alert Type Location Threshold Criteria
Advisory National, except Nunavik* When a period of freezing drizzle is expected for at least eight hours.

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

Freezing Rain

Table 9. Alerting Parameters Environment Canada uses for issuing a Freezing Rain Warning
Alert Type Location Threshold Criteria
Warning British Columbia, Yukon, Alberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Ontario and Quebec (except Nunavik*) When freezing rain is expected to pose a hazard to transportation or property;
Or
When freezing rain is expected for at least two hours.
Warning Nova Scotia, New Brunswick, Prince Edward Island, Magdalen Islands, Newfoundland and Labrador When freezing rain is expected to pose a hazard to transportation or property;
Or
When freezing rain is expected for at least four hours.

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

Frost

Table 10. Alerting Parameters Environment Canada uses for issuing a Frost Advisory
Alert Type Location Threshold Criteria
Advisory Southern 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.

Heat

Table 11. Alerting parameters Environment Canada uses for issuing a Heat Warning
Alert Type Location Threshold Criteria
Warning Newfoundland and Labrador, New Brunswick, Nova Scotia and Prince Edward Island Issued when humidex value or temperature expected to reach 40 or higher for at least one hour.
Warning Quebec, except Nunavik* Issued when the humidex value is 40 or higher and when the temperature is 30°C or warmer, and both conditions persist for at least one hour.
Or
Issued when temperature is 40°C or warmer.
Warning Ontario - extreme southwest (Essex and Chatham-Kent Counties) Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 31°C or warmer and nighttime minimum temperatures are expected to fall to 21°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 42 or higher.
Warning Ontario - remainder of southern Ontario (including the District of Parry Sound) Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 31°C or warmer and nighttime minimum temperatures are expected to fall to 20°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 40 or higher.
Warning Ontario - North Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 29°C or warmer and nighttime minimum temperatures are expected to fall to 18°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 36 or higher.
Warning Manitoba - South Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 32°C or warmer and nighttime minimum temperatures are expected to fall to 16°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 38 or higher.
Warning Manitoba - North Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 29°C or warmer and nighttime minimum temperatures are expected to fall to 16°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 34 or higher.
Warning Saskatchewan - South (excluding Meadow Lake, The Battlefords, Prince Albert, and Hudson Bay) Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 32°C or warmer and nighttime minimum temperatures are expected to fall to 16°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 38 or higher.
Warning Saskatchewan - North and Central (including Meadow Lake, The Battlefords, Prince Albert, and Hudson Bay) Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 29°C or warmer and nighttime minimum temperatures are expected to fall to 14°C or warmer.
Or
Issued when 2 or more consecutive days of humidex values are expected to reach 34 or higher.
Warning Alberta - Extreme south (including Pincher Creek, Cardston, Lethbridge, and Medicine Hat) Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 32°C or warmer and nighttime minimum temperatures are expected to fall to 16°C or warmer.
Warning Alberta - Remainder of Alberta (including the Cities of Edmonton, Red Deer and Calgary) Issued when 2 or more consecutive days of daytime maximum temperatures are expected to reach 29°C or warmer and nighttime minimum temperatures are expected to fall to 14°C or warmer.
Warning British Columbia - Metro Vancouver, Fraser Valley, Howe Sound, Whistler, Sunshine Coast only. Issued when the average of today’s 2 PM temperature and tomorrow’s forecast high is expected to equal or exceed 29°C at the Vancouver International Airport.
Or
Issued when the average of today’s 2 PM temperature and tomorrow’s forecast high is expected to equal or exceed 34°C at the Abbotsford Airport.
Warning Northwest Territories and Nunavut Issued when humidex value or temperature expected to reach or exceed 40°C.

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

Hurricane

Table 12. Alerting Parameters Environment Canada uses for issuing a Hurricane Watch and/or Warning
Alert Type Location Threshold Criteria
Watch National, including all coastal and inland regions When, 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 (average sustained winds of 118 km/h or higher) threatening the area.
Warning National, including all coastal and inland regions When 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 13. Alerting parameters for a Short Duration Rainfall (Heavy Downpour) Warning
Alert Type Location Threshold Criteria
Warning Alberta, Saskatchewan, Manitoba, Ontario, and Quebec (except Nunavik*) When 50 mm or more of rain is expected within one hour.
Warning Interior dry sections of British Columbia When 15 mm or more of rain is expected within one hour.
Warning Remaining sections of British Columbia, Yukon, Northwest Territories, Nunavut,
New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and Labrador
When 25 mm or more of rain is expected within one hour.

Table 14. Alerting parameters Environment Canada uses for issuing a Long Duration Rainfall Warning in the Summer
Alert Type Location Threshold Criteria
Warning National, except Nunavik* and portions of British Columbia, as specified below When 50 mm or more of rain is expected within 24 hours;
or
When 75 mm or more of rain is expected within 48 hours.
Warning NEW - Interior dry sections of British Columbia When 25 mm or more of rain is expected within 24 hours.
Warning Inland Vancouver Island,  West Vancouver Island, North Vancouver Island, Central Coast - coastal sections, and North Coast - coastal sections When 100 mm or more of rain is expected within 24 hours.

Table 15. Alerting parameters Environment Canada uses for issuing a Long Duration Rainfall Warning in the Winter
Alert Type Location Threshold Criteria
Warning National, except Nunavik* and British Columbia When 25 mm or more of rain is expected within 24 hours.
Warning British Columbia, except except Inland Vancouver Island,  West Vancouver Island,
North Vancouver Island, Central Coast - coastal sections, and North Coast - coastal sections
When 50 mm or more of rain is expected within 24 hours;
or
When 75 mm or more of rain is expected within 48 hours.
Warning Inland Vancouver Island,  West Vancouver Island, North Vancouver Island,
Central Coast - coastal sections, and North Coast - coastal sections
When 100 mm or more of rain is expected within 24 hours.

Table 16. Alerting parameters Environment Canada uses for issuing a Long Duration Rainfall Warning during a Thaw Only
Alert Type Location Threshold Criteria
Warning Interior British Columbia, Fort Nelson, Muncho Lake Park - Stone Mountain Park, Dease Lake, Cassiar Mountains, and Atlin When 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 17. Alerting parameters Environment Canada uses for issuing a Severe Thunderstorm Watch and/or Warning
Alert Type Location Threshold Criteria
Watch National, except Nunavik*
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).
Warning National, except Nunavik*
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 18. Alerting parameters Environment Canada uses for issuing a Snowfall Warning
Alert Type Location Threshold Criteria
Warning
Newfoundland and Labrador, New Brunswick, Nova Scotia, Prince Edward Island, Magdalen Islands, Quebec (except Nunavik*), Ontario and the following regrions of British Columbia:

Whistler, Howe Sound, Inland Vancouver Island, North Columbia, West Columbia, Kinbasket, Elk Valley, Yoho Park - Kootenay Park, North Coast - Inland Sections, West Kootenay, Arrow Slocan Lakes, Kootenay Lake, Cassiar Mountains
When 15 cm or more of snow falls within 12 hours or less.
Warning British Columbia: Southern and Central Coast - coastal sections When 10 cm or more of snow falls within 12 hours or less;
or
When five cm or more of snow falls within six hours or less.
Warning Haines Skagway roads, Yukon / British Columbia When 20 cm or more of snow falls within 24 hours or less.
Warning Alberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Yukon, and all remaining areas of British Columbia When 10 cm or more of snow falls within 12 hours or less.

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

Snow Squall

Table 19. Alerting parameters Environment Canada uses for issuing a Snow Squall Watch
Alert Type Location Threshold Criteria
Open-Water
Watch National, except Nunavik*
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.
Frontal
Watch National, except Nunavik* When conditions are favourable for the development of brief periods of very poor visibilities caused by heavy snow and blowing snow.

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

Table 20. Alerting parameters Environment Canada uses for issuing a Snow Squall Warning
Alert Type Location Threshold Criteria
Open-Water
Warning National, except Nunavik*
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.
Frontal
Warning National, except Nunavik* When there is a brief period (less than one hour) of very poor visibility (400 m or less), caused by heavy snow and blowing snow, and accompanied by strong, gusty winds of 45 km/h 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 21. Alerting parameters Environment Canada uses for issuing a Storm Surge Warning
Alert Type Location Threshold Criteria
Warning Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, Quebec - along the St. Lawrence and Gulf of St. Lawrence coastal areas and the Magdalen Islands 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 22. Alerting parameters Environment Canada uses for issuing a Tornado Watch and/or Warning
Alert Type Location Threshold Criteria
Watch National, except Nunavik* When conditions are favourable for the development of severe thunderstorms with one or more tornadoes.
Warning National, except Nunavik* 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 23. Alerting parameters Environment Canada uses for issuing a Tropical Storm Watch and/or Warning
Alert Type Location Threshold Criteria
Watch National, 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 (average sustained winds 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).
Warning National, including all coastal and inland regions When coastal and/or coastal winds of 63 to 117 km/h caused by a tropical cyclone are expected to occur.

Tsunami

Table 24. Alerting parameters Environment Canada uses for issuing a Tsunami Alert
Alert Type Location Threshold Criteria
Advisory East Coast : Coastal areas of Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, and areas of Quebec adjacent to the St. Lawrence River estuary and Gulf of St. Lawrence

West Coast : Coastal areas and inlets of British Columbia

A tsunami advisory indicates a tsunami with the potential to produce strong currents or waves and is dangerous to those in or very near the water is imminent, expected, or occurring.

Large inundations are not expected in areas under advisory status.

Note: Tsunami advisories are issued in partnership with provincial and federal organizations in response to a mesage from the National Tsunami Warning Center.

Warning East Coast : Coastal areas of Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, and areas of Quebec adjacent to the St. Lawrence River estuary and Gulf of St. Lawrence

West Coast : Coastal areas and inlets of British Columbia

A tsunami warning indicates that a tsunami is imminent, expected, or occurring and that coastal locations in the warned area should expect widespread flooding.

Note: Tsunami warnings are issued in partnership with provincial and federal organizations in response to a mesage from the National Tsunami Warning Center.

Watch East Coast : Coastal areas of Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, and areas of Quebec adjacent to the St. Lawrence River estuary and Gulf of St. Lawrence

West Coast : Coastal areas and inlets of British Columbia

A tsunami watch is an early alert issued to areas which may later be impacted by a tsunami.

Note: Tsunami watches are issued in partnership with provincial and federal organizations in response to a mesage from the National Tsunami Warning Center.

Weather

Table 25. Alerting parameters Environment Canada uses for issuing a Weather Advisory and/or Warning
Alert Type Location Threshold Criteria
Advisory National, except Nunavik* A generic weather advisory.
One example might be on days when funnel clouds are expected, but a Tornado alert would not be appropriate.
Warning National, except Nunavik* A generic weather warning may be issued for extreme weather events for which there is no suitable warning type, because they rarely occur.

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 26. Alerting parameters Environment Canada uses for issuing a Wind Warning
Alert Type Location Threshold Criteria
Warning National
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.
Warning Except:
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.
Warning Except:
British Columbia

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

Winter Storm**

Table 27. Alerting parameters Environment Canada uses for issuing a Winter Storm Watch and/or Warning
Alert Type Location Threshold Criteria
Watch National, except Nunavik*
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.
Warning National, except Nunavik*
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 cold.
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.

Additional information in all alerts

The alert statements will include impact and call-to-action statements, designed to help Canadians be more aware of the risk of severe weather. This will allow them to take appropriate action to protect themselves, their families and their property.

A Call to Action statement provides information on how Canadians can protect themselves, family or property in this specific set of circumstances - some examples of a Call to Action statement are:

  • Strong winds can cause unusually high waves. Keep a safe distance from the waterfront to avoid being swept away.
  • It is recommended to stay indoors. If this is not possible, limit time spent outdoors and exposure to the cold as much as possible to reduce the risk of frostbite and hypothermia.
  • Public Safety Canada encourages everyone to make an emergency plan and get an emergency kit with drinking water, food, medicine, a first-aid kit and a flashlight.

An Impact statement is designed to indicate what could happen if the forecast conditions occur - some examples of an Impact statement are:

  • Surfaces such as highways, roads, walkways and parking lots will become icy, slippery and extremely hazardous.
  • Be prepared for winter conditions at higher elevations.

Twitter hashtags, such as #bcstorm and #ONstorm will also be included in the alert statements so that Canadians can report local severe weather observations to Environment Canada. Note that hashtags are case-insensitive.

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
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