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 alerts (watches or warnings) are also accompanied by a colour, which is determined by the potential impacts of the event and its confidence, ranging from moderate to very high. Special weather statements are not accompanied by a colour.
Yellow alert: This is the most common type of warning issued. Hazardous weather may cause damage, disruption, or health impacts, but impacts will be moderate, localized and/or short-term. Yellow alerts are also issued when there is the possibility of high or very high impacts, but forecast confidence is low to moderate. Orange alert: These are uncommon and indicate that severe weather is likely to cause significant damage, disruption, or health impacts. Impacts are major, widespread and/or may last a few days. Orange alerts are only issued when forecast confidence is high and there are likely to be high impacts. Red alert: Red alerts are the rarest, and indicate very dangerous and possibly life-threatening weather will cause extreme damage and disruption. Impacts are extensive, widespread, and prolonged. These are only issued for very high impact events with very high forecast confidence. Low impact events are not given a colour, but they may result in the issuing of a Special Weather Statement if appropriate.
Warnings colour table
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. No other types of watches or warnings are 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 (2.5 cm or more in diameter) Damaging winds (Gusts 90 km/h (56 mph) or greater) Heavy rain (Alberta, Saskatchewan, Manitoba, Ontario, and Quebec: 50 mm (2.0 in) or more per hour. Interior dry sections of British Columbia: 15mm or more rain in one hour. Remaining sections of British Columbia, Yukon, Northwest Territories, Nunavut, New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and Labrador: 25 mm (0.98 in) per hour. Nunavik: 50 mm or more of rain in one 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 (2.5 cm or more in diameter) Damaging winds (Gusts 90 km/h (56 mph) or greater) Heavy rain (Alberta, Saskatchewan, Manitoba, Ontario, and Quebec: 50 mm (2.0 in) or more per hour. Interior dry sections of British Columbia: 15mm or more rain in one hour. Remaining sections of British Columbia, Yukon, Northwest Territories, Nunavut, New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and Labrador: 25 mm (0.98 in) per hour. Nunavik: 50 mm or more of rain in one 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
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