Severe weather terminology (Canada)

This article describes severe weather terminology used by the Meteorological Service of Canada, a branch within Environment and Climate Change Canada. The article primarily describes various weather warnings, and their criteria. Related weather scales and general weather terms are also addressed in this article. Some terms are specific to certain regions.

Warning categories

Severe weather bulletins are issued as a watch or a warning, depending on the risk or severity of the event.

*Watches are issued when conditions are favourable for the development of severe weather, but the occurrence, location, and/or timing is still too uncertain to issue a warning. The target lead time for severe thunderstorm watches is typically six hours before the event, whereas watches for winter events have a target lead time of 12 to 24 hours in advance. Watches are intended to raise awareness of the public to the potential for hazardous weather conditions, and typically serve as a lead-up to a warning.
*Warnings are issued when severe weather is either imminent or occurring. Warnings for synoptic scale events such as snowstorms are issued with an ideal lead time of at least six, and up to 24 hours. Severe thunderstorm warnings and tornado warnings, by their nature, will typically be issued with very little lead time. Weather warnings are usually issued for regular forecast regions affected. Severe thunderstorm and tornado warnings, however, might be issued specifically for smaller warning or "sub-regions" within the regular forecast area where available.
*Advisories are issued in a similar format to that of an official warning. Unlike warnings, however, these types of bulletins describe exceptional weather events that are generally not considered hazardous, such as frost.
*Special Weather Statements are free form statements that are typically used to describe weather hazards that cannot be described by another watch, warning, or advisory; is not hazardous enough to warrant issuing a watch or warning; or to warn the public of a potentially hazardous weather event in the long term forecast.
Alerts are typically updated every six hours, except for mesoscale/summer severe weather alerts which are updated when necessary.

Weather warnings

Weather watches and warnings are issued when potentially hazardous weather is occurring or is forecast for the short term period.

Note: Nunavik, Quebec only participates in two types of weather warnings: Extreme Cold Warnings and Wind Warnings. All other watches and warnings are not issued in this region of the country.

Mesoscale/Summer severe weather

* Severe Thunderstorm Watch (SAME event code: SVA) – Issued when the potential exists for the development of severe thunderstorms, which are capable of producing one or more of the following:
** Large hail (2 cm or more in diameter)
** Damaging winds (Gusts or greater)
** Heavy rain (Alberta to Southern Quebec: or more per hour. Pacific, Northern and Maritime provinces: per hour)
* Severe Thunderstorm Warning (SVR) – Issued when a severe thunderstorm is detected on radar or are observed by those in the immediate area. A warning is issued when one or more of the following has been detected or highly possible:
** Large hail (2 cm or more in diameter)
** Damaging winds (Gusts or greater)
** Heavy rain (Alberta to Southern Quebec: or more per hour. Pacific, Northern and Maritime provinces: per hour)

Public bulletins will often mention the possibility of tornadoes; if a tornado is spotted or conditions are favourable enough for tornado development, the warning will be upgraded accordingly.

* Tornado Watch (TOA) – Issued when conditions are favourable for the development of severe thunderstorms with one or more tornadoes. Tornado Watches are also issued when cold core funnel clouds are possible and pose a threat to people on the ground. If cold core funnel clouds are not expected to touch down, a weather advisory will be issued instead. If there is a landspout on the ground, a Tornado Warning will be issued.

* Tornado Warning (TOR) – Issued when one or more tornadoes are occurring in the area specified or rotation is detected on Doppler weather radar, or when someone spots a supercell tornado or a landspout on the ground. The exact location of the tornado or storm will be given in the statement.

Hurricanes and other tropical systems

* Tropical Storm Watch (TRA) – Issued when a tropical storm or tropical storm conditions pose a threat to coastal areas generally within 36 hours. A watch will generally cover a larger threat area than a warning, as the uncertainty on the track of the storm is greater.
* Tropical Storm Warning (TRW) – Issued when winds of are expected. Warnings are not issued more than 24 hours in advance.
* Hurricane Watch (HUA) – Issued when a hurricane approaches the mainland and is considered a threat to coastal and inland regions.
* Hurricane Warning (HUW) – Issued for coastal waters where winds greater than are expected. It may also include areas where storm surge or exceptionally high waves are predicted, even though winds may be less than hurricane force. Warnings are not issued more than 24 hours in advance. If the path is erratic or if the hurricane undergoes a transition into a post-tropical system, the warning may only be issued a few hours in advance. Almost always accompanied by a Wind Warning.
* Storm Surge Warning – Issued when a storm surge and/or high waves may result in significant flooding in coastal areas. Sometimes issued during strong Nor'easters or other non-tropical storms.

Winter weather

* Winter Storm Watch (WSA) – Issued when conditions are favourable for the development of hazardous winter conditions, including:
** a blizzard.
** a major snowfall of or more in a 24-hour period.
** a significant snowfall (snowfall warning criteria) combined with another winter hazard such as freezing rain, strong winds, blowing snow and/or extreme cold.
* Winter Storm Warning (WSW) – Issued when hazardous winter conditions are expected or occurring, including:
** a major snowfall of or more in a 24-hour period.
** a significant snowfall (snowfall warning criteria) combined with another winter hazard such as freezing rain, strong winds, blowing snow and/or extreme cold.
* Blizzard Warning (BZW) – Issued when winds of or more, are expected to cause widespread reductions in visibilities to less than , due to blowing snow, for at least four hours (except six hours north of the tree line).
* Snowfall Warning (WSW) – Issued when significant amounts of snow are expected to fall over a 12-hour period. These amounts vary across the country due to topographical and climatic considerations. Criteria ranges from in a 12-hour period, with local exceptions for southwestern British Columbia ( in a 6-hour period) and Haines Skagway roads in British Columbia/Yukon ( in a 24-hour period).
*Snow Squall Watch – There are two types of snow squalls of which alerts are issued for:
**Open-Water – Issued when, down wind of a large body of water, conditions are favourable for the development of snow squalls with one or more of the following conditions:
*** Local, intense snowfall resulting in accumulations of or more in 12 hours or less.
*** Reduced visibility less than , caused by snowfall, with or without blowing snow, for 3 hours or more.
**Frontal – Issued when conditions are favourable for the development of snow squalls that produce brief periods of very poor visibilities caused by heavy snow and blowing snow caused by the passage of a cold front.
* Snow Squall Warning (WSW) – There are two types of snow squalls of which alerts are issued for:
**Open-Water – Issued when, down wind of a large body of water, snow squalls are imminent or occurring with one or more of the following conditions:
*** Local, intense snowfall resulting in accumulations of or more in 12 hours or less.
*** Reduced visibility less than , caused by snowfall, with or without blowing snow, for 3 hours or more.
**Frontal – Issued when a brief period (less than one hour) of poor visibility of or less caused by heavy snow and blowing snow, accompanied by strong, gusty winds of or more, is expected or occurring with the passage of a cold front.
* Freezing Rain Warning (WSW) – Issued when freezing rain is expected to create a hazard to transportation and property, or when freezing rain is expected to persist for at least 2 hours (4 hours in Atlantic Canada and Magdalen Islands).
*Flash Freeze Warning (FSW) – A rapid drop in temperatures, causing freezing of residual water on roads, and sidewalks to quickly build up.

General warnings

* Wind Warning (HWW) – Varies based on climatology across the country.
** The national criteria, before exceptions, is when sustained winds of or greater, or wind gusts of or greater, are expected or occurring. Les Suêtes ( Cape Breton) wind warnings are issued for local wind effects using the national criteria.
** Wind warning criteria for Southwestern Alberta, Dempster Highway (Yukon), Western Vancouver Island, and Newfoundland and Labrador is when sustained winds of or greater, or wind gusts of or greater, are expected or occurring.
** Wind warning criteria for North Vancouver Island, North Coast (British Columbia), Central Coast (British Columbia), and Haida Gwaii, is when sustained winds of or greater, or wind gusts of or greater, is expected or occurring.
* Rainfall Warning – Local rainfall thresholds vary considerably across Canada and reflect a potential for regional flooding. Seasonal variations of the warning exist to accommodate flooding potential due to the frozen ground’s reduced ability to absorb rainfall and snow melt. The national criteria during the winter is or more in 24 hours. The national criteria in the summer is or more in 24 hours or or more in 48 hours. Regional exceptions apply to different parts of British Columbia, with higher criteria for coastal areas and lower criteria for interior dry regions.
* Heat Warning – Criteria varies considerably across the country and considers combinations of expected maximum temperatures, minimum temperatures, and humidex values. Warnings will be issued when criteria is expected to be met for at least two consecutive days (except Quebec, where criteria only needs to be met for at least one hour).
* Extreme Cold Warning – Criteria varies across the country, ranging from in some Arctic regions to in southwestern Ontario. Warnings will be issued when the air temperature or wind chill is expected to meet the regional criteria for at least two hours.
* Arctic Outflow Warning – An Arctic Outflow Warning is based on a combination of wind speed and temperatures which produce wind chills of at least for at least six hours during the winter when very cold Arctic air breaks from the interior mainland of British Columbia and spills out through mountain gaps and fjords.
* Dust Storm Warning (DSW) – Issued only in the Prairie Provinces when blowing dust caused by high winds is expected to reduce visibility to or less for one hour or more.
* Storm Surge Warning – Issued for abnormally high water levels and high waves caused by storms, which have the potential to cause coastal flooding. This usually occurs when astronomical tides are at their maximum.
* Weather Warning – 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, for 50 km/h winds following an ice storm which could cause structural wind damage, even if the wind warning criteria of is not expected to be reached.

Marine warnings

* Strong Wind (Small Craft) Warning – Issued if winds of are forecast.
* Gale

HOME


Content is Copyleft
Website design, code, and AI is Copyrighted (c) 2014-2017 by Stephen Payne


Consider donating to Wikimedia



As an Amazon Associate I earn from qualifying purchases