Severe weather terminology (Canada) - AbsoluteAstronomy.com

This article describes Severe weather
Severe weather
Severe weather phenomena are weather conditions that are hazardous to human life and property.- Examples Include :Severe weather can occur under a variety of situations, but three characteristics are generally needed: a temperature or moisture boundary, moisture, and , instability in the...

Terminology used by the Environment Canada

Environment Canada

Environment Canada , legally incorporated as the Department of the Environment under the Department of the Environment Act Environment Canada (EC) (French: Environnement Canada), legally incorporated as the Department of the Environment under the Department of the Environment Act Environment...

's Meteorological Service of Canada

Meteorological Service of Canada

The Meteorological Service of Canada , also known as "The Canadian Weather Service", is a division of Environment Canada, which primarily provides public meteorological information and weather forecasts and warnings of severe weather and other environmental hazards...

. This article primarily describes various weather warnings, and their criteria. Related weather scales and general weather terms are also addressed in this article. Some terms may be 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. Less severe events that could be a cause for concern will be issued as a special weather statement or Advisory.

Watches are issued as a "heads-up", that conditions are favourable for the development of severe weather. A watch in the summer is typically issued up to six hours in advance, and in the case of winter events at least 12 to 24 hours in advance. Weather watches are issued for regular forecast regions affected.

Warnings are issued when severe weather is either imminent or occurring in the given area. Warnings for large scale events such as snowstorms are issued ideally with at least six, and up to 24 hours lead time. Severe thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...

warnings, by their nature, will be issued less than one hour in advance. Weather warnings are usually issued for regular forecast regions
Forecast region
A forecast region is a unique geographical area for which individual weather reports are issued.-Canada:In Canada, the Meteorological Service divides the country into several forecast regions for the purpose of issuing routine text forecasts and weather warnings, as Canada's provinces and...

affected. Severe Thunderstorm and Tornado warnings however, may be issued specifically for smaller warning or "sub-regions" within the regular forecast area where available. Specific warning criteria varies by region, depending on geography, or other conditions in which a specific region may be vulnerable.

Special Weather Statements or Advisories are issued in a free style format for weather events that are unusual, cause general inconvenience or public concern and cannot adequately be described in a public weather forecast. They may reflect a warning in effect near the USA border. A Special Weather Statement may also be issued to indicate any potentially hazardous situation in the long term forecast.

Updated statements, watches and warnings are reissued or upgraded if required.

Weather Warnings

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

Local-Scale/Summer Severe Weather

Due to its local-scale nature, a watch is typically issued in advance for public forecast areas where conditions may be favorable for the development of severe weather. A warning is issued for areas where severe weather is imminent or occurring. Unlike other warnings, these are issued for smaller warning areas within its regular forecast region.

Severe Thunderstorm Watch - 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 90 Km/h or greater)
- Heavy Rain (Alberta to Southern Quebec: 50 mm or more per hour. Pacific, Northern and Maritime provinces: 25mm per hour)

Severe Thunderstorm warning: 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 90 Km/h or greater)
- Heavy Rain (Alberta to Southern Quebec: 50 mm or more per hour. Pacific, Northern and Maritime provinces: 25mm 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 - Issued when conditions are favorable for the development of severe thunderstorms with one or more tornadoes. A tornado watch may also be issued if there are a certain number of funnel clouds (generally cold-core type) spotted over a certain area, or if there is a reasonable probability landspouts or waterspouts developing.

Tornado warning: Issued when one or more tornadoes are occurring in the area specified or are detected on Doppler radar. The expected motion, development and duration will be given in the warning.

Hurricanes or Tropical Disturbances

Tropical Storm Watch - 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 - Issued when winds of 63 to 117 kilometers per hour are expected. Warnings are not issued more than 24 hours in advance.

Hurricane Watch - Issued when a hurricane approaches the mainland and is considered a threat to coastal and inland regions.

Hurricane Warning - Issued for coastal waters where winds greater than 117 km/h 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 post tropical transition, the warning may only be issued a few hours in advance.

Storm Surge Warning - Issued when a storm surge and/or high waves may result in significant flooding in coastal areas.

Winter Severe Weather

Winter Storm Watch - Issued when conditions are favorable for the development of hazardous conditions. These bulletins may be issued 48 to 60 hours in advance.

Winter Storm Warning - Issued when a combination of hazardous winter conditions are occurring or expected to develop no more than 12 to 14 hours in advance.

Blizzard Warning - Issued when winds of 40 km/h or more, are expected to cause widespread reductions in visibilities to less than one kilometre, due to blowing snow, for at least four to six hours and windchill is expected to be high.

Blowing Snow warning - Issued when high winds and snow reduce visibility to less than 1 km (<5/8 mile), but not necessarily meet the blizzard definition for duration and temperature.

Snowfall warning - Issued when hazardous amounts are expected to fall over a 12- or 24-hour period. These amounts vary across the country due to topographical and climatic considerations. They range from five cm in 24 hours for parts of southwestern BC
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

to 15, 20 and even 25 cm in 24 hours elsewhere.

Snowsquall warning - Issued when 15 cm or more of snow is expected to fall within 12 hours, or the visibility is likely to be near zero for at least four hours because of falling and blowing snow. These are for areas much smaller than a snowstorm would cover. A warning may also be issued when blizzard-like conditions are expected to develop in the vicinity of a cold front for short periods.

Freezing Rain / Freezing Drizzle Warning - Issued when slippery walking and driving conditions are expected. A warning may be issued if ice is over 2mm thick and could damage to trees and overhead wires.

General Warnings

Wind warning - when blowing steadily at 60-65 km/h or more, or winds gusting to 90 km/h or more. Les Suêtes (Cape Breton) and Wreckhouse (Southwestern Newfoundland) Winds Warning are for local effect winds.

Rainfall warning - Local rainfall thresholds vary considerably across Canada and reflect a potential for regional flooding. Some seasonal considerations are made for ground that is frozen or sodden.

High Heat and Humidity Warning - Issued when temperatures at least 30°C, and humidex values over 40 persist for at least 1 hour. Issued in Quebec only.

Frost Warning - A Frost Warning is issued only when air temperatures are expected to fall to near freezing or below during the local growing season. A frost warning would normally be issued when forecast air temperature is +2°C or below.

Wind Chill Warning - Wind chill warning criteria vary across the country, ranging from -55 in some Arctic regions to -30 in southwestern Ontario. Warnings will be issued when the winds are expected to be at least 15 km/h and these extreme wind chills will persist for at least three 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 -20 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.

Cold Wave Warning - When temperatures are expected to fall dramatically within 24 hours from above normal or near seasonal temperatures to very cold temperatures a Cold Wave Warning is issued in some parts of the country.

Flash Freeze warning - When conditions are likely to rapidly cause the temperature to drop within two to three hours, from above the freezing mark to below the freezing mark, and the roads are wet roads from prior rain or wet snow during the time of rapid cooling.

Dust Storm: issued only in the Prairie Provinces when blowing dust caused by high winds is expected to reduce visibility to one kilometre or less for one hour or more.

Marine Warnings

Strong Wind (Small Craft) Warning - Issued if winds of 20 to 33 knots are forecast

Gale Warning - Issued if winds of 34 to 47 knots are forecast

Storm Warning - Issued if winds of 48 to 63 knots are forecast

Hurricane Force Wind Warning - Issued for winds of 64 knots or greater

Squall warning: Issued for forecast or observed wind gusts of 34 knots or greater that are associated with a line, or an organized area, of thunderstorms.

Freezing Spray Warning - Freezing spray occurs when a combination of low temperatures and strong winds cause sea spray to freeze on a ship's superstructure or on other structures either in the sea or near the water's edge. A weather warning is issued whenever moderate or heavy ship icing is expected.

Waterspout Warning/Alert - Issued commonly for Atlantic provinces (usually M-IS). Issued when a waterspout is spotted on radar or is seen in person by trained spotters. Warning is commonly to warn persons on water. A waterspout warning can be sometimes issued for an area on land if it is supected that the funnel will travel inland.

Advisories

Advisories are issued as part of a special weather statement 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, but may be a potential concern to the public (eg. High Humidex that may affect certain age groups). Advisories may also be issued for potentially hazardous weather in the long term forecast. Commonly issued advisories include:

Humidex Advisory - Issued when Humidex values exceed local criteria; most areas will issue an advisory if the Humidex is expected to be over 40.

Air Quality Advisory - In partnership with the various provinces when standards are exceeded an Air Quality Advisory (British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

), Smog Watch and Smog Advisory (Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

), Air Quality and Health Advisory (Atlantic Canada
Atlantic Canada
Atlantic Canada is the region of Canada comprising the four provinces located on the Atlantic coast, excluding Quebec: the three Maritime provinces – New Brunswick, Prince Edward Island, and Nova Scotia – and Newfoundland and Labrador...

) or Smog Warning (Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....

) is issued by the provinces.

Fog or Smoke Advisory- Issued to highlight widespread fog that is giving reduced visibilities less than one km or to explain hazy skies, reduced visibilities due to forest fire smoke or blowing dust in the winter.

Hurricane Information Statements

Issued when a tropical system threatens Canadian coastal waters or land. The statement includes public and marine impacts and warning summary, location and expected motion of the storm and technical discussion. This information is updated at least every six hours.

Thunderstorm Potential

Issued in Ontario only, these statements are issued twice daily from May through September. These statements give an in-depth description of general thunderstorm potential for the next 48 hours, whether severe or non-severe.

Fujita Scale

The Fujita Scale
Fujita scale
The Fujita scale , or Fujita-Pearson scale, is a scale for rating tornado intensity, based primarily on the damage tornadoes inflict on human-built structures and vegetation...

, is a scale for rating tornado intensity based on the damage on human-built structures and vegetation. While the United States has adopted the Enhanced Fujita (EF) Scale since 2007, Environment Canada still continues to use the original Fujita Scale to assess tornado intensity. Tornadoes exceeding F2 intensity are rare in Canada, though several tornadoes such as the Edmonton Tornado

Edmonton Tornado

The Edmonton Tornado, an event also known as Black Friday to Edmontonians, was a powerful and devastating tornado that ripped through the eastern part of Edmonton, Alberta, Canada and parts of neighbouring Strathcona County on the afternoon of Friday, July 31, 1987.The tornado remained on the...

in 1987, have been as strong as F4. The only recorded F5 tornado to date was the Elie, Manitoba Tornado

Elie, Manitoba Tornado

The Elie, Manitoba Tornado was an F5 tornado that struck the town of Elie, Manitoba, Canada, on June 22, 2007. While several houses were leveled, no one was injured or killed by the tornado. Two well-built homes in the town were swept clean off of their foundations, justifying the F5...

in 2007.

Saffir-Simpson Hurricane Scale

The Saffir-Simpson Hurricane Scale
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

is used by the Canadian Hurricane Centre

Canadian Hurricane Centre

The Canadian Hurricane Centre is a division of the Meteorological Service of Canada, an agency of Canada's Department of the Environment, which exists to advise Canadians on the threat of tropical cyclones such as hurricanes and tropical storms...

for hurricanes affecting the East Coast of Canada. The Scale ranges from Category 1, the weakest, to Category 5 the strongest with sustained winds exceeding 250km/h.

External links

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