Public Alerting Criteria
Environment Canada issues alert bulletins for the following weather hazards:
- Blizzard
- Blowing Snow
- Dust Storm
- Flash Freeze
- Freezing Drizzle
- Freezing Rain
- Frost
- High Heat and Humidity
- Humidex
- Hurricane
- Rainfall
- Severe Thunderstorm
- Snowfall
- Snow Squall
- Storm Surge
- Tornado
- Tropical Storm
- Tsunami
- Weather
- Wind
- Wind Chill
- Winter Storm
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
| 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | 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
| 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. |
Flash Freeze
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National, 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National, 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | British 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. |
| 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 4 hours. |
*No alert of this type exists for this region at this moment.
Frost
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | 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. |
*No alert of this type exists for this region at this moment.
High Heat and Humidity
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | Quebec | Issued 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Statement Advisory | Alberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Ontario, Nova Scotia, and New Brunswick | Issued when the heat and humidity conditions exceed local criteria values. |
Hurricane
| 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 (sustained gales 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | Alberta, Saskatchewan, Manitoba, Ontario, and Quebec (except extreme Northern Quebec*) | When 50 mm or more of rain is expected within one hour. |
| Warning | 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. |
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National, except extreme Northern Quebec* 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 | 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. |
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National, except extreme Northern Quebec* and British Columbia | When 25 mm or more of rain is expected within 24 hours. |
| Warning | British Columbia, except | 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. |
| 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Watch | National, except extreme Northern Quebec* | When conditions are favourable for the development of severe thunderstorms with one or more of the following conditions:
|
| Warning | National, 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:
|
*No alert of this type exists for this region at this moment.
Snowfall
| Alert Type | Location | Threshold 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. |
| Warning | Alberta, Saskatchewan, Manitoba, Northwest Territories, Nunavut, Yukon, British Columbia -all regions not specified elsewhere | When 10 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 5 cm or more of snow falls within 6 hours or less. |
| Warning | Haines Skagway roads, Yukon | When 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Watch | National, 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:
Note that local snow accumulations may be significant. |
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | Location | Threshold Criteria |
| Warning | National, 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:
Note that local snow accumulations may be significant. |
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National, 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | Nova 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Watch | National, except extreme Northern Quebec* | When conditions are favourable for the development of severe thunderstorms with one or more tornadoes. |
| Warning | National, 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | 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 (sustained gales of 63-117 km/h) threatening the area. This watch could be issued for:
|
| 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | East 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
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National, 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
| 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 Queen Charlottes | 90 km/h or more sustained wind; and/or Gusts to 110 km/h or more. |
Wind Chill
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Warning | National | Issued 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. A national wind chill program is in development. |
Winter Storm**
| Alert Type | Location | Threshold Criteria |
|---|---|---|
| Watch | National, except extreme Northern Quebec* | When conditions are favourable for the development of severe and potentially dangerous winter weather, including:
|
| Warning | National, except extreme Northern Quebec* | When severe and potentially dangerous winter weather conditions are expected, including:
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.
- Date Modified: