Severe thunderstorm warning

A severe thunderstorm warning (SAME code: SVR) is a type of public warning for severe weather that is issued by weather forecasting agencies worldwide when one or more severe thunderstorms have been detected by Doppler weather radar, observed by weather spotters, or reported by an emergency management agency, law enforcement, or the general public. Unlike a watch, a warning is issued to areas in the direct path of active severe thunderstorms, that are expecting a direct impact typically within an hour. Severe thunderstorms can cause property damage and injury due to large hail, high winds, and flooding due to torrential rainfall. The exact criteria to issue a warning varies from country to country.

Not to be confused with Severe thunderstorm watch.

In the United States, the National Weather Service issues a warning when an observed thunderstorm is producing wind gusts of at least 58 miles per hour (93 km/h), or hail of at least 1 inch (2.5 cm) in diameter. Most forecasting agencies have similar criteria, but some agencies, such as Environment Canada, also include high rainfall rate. Others may instead issue a flood advisory or in the case of the National Weather Service, a flash flood warning.^[1]

Tornado – indicates the mesocyclone of the parent severe thunderstorm is producing circulation at or near the cloud base, which may warrant the issuance of a tornado warning if base-level rotation strengthens. When incorporated into the storm impact summary, the tornado tag (appearing in applicable severe thunderstorm warning products as “TORNADO...POSSIBLE”) will precede the wind and hail tags.

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Hail – indicates the estimated size of hail (measured in inches) being produced by the parent severe thunderstorm (e.g., “HAIL...1.25IN”). When included, the “Impact” section of the warning text will describe potential damage impacts from the hailstones, with the impact message varying in severity depending on radar estimated or observed reports of measured large hail (e.g., “Hail damage to vehicles is expected.”) and the “Hazard” section will provide a comparison of the size of hailstones to objects of similar size (e.g., “baseball size hail” for hailstones measuring 2.75"). (If the tag lists either “HAIL...0.00IN”, indicating no hail is accompanying the storm, or “HAIL...<.75IN”, indicating hailstones below severe criteria that may range in equivalent size from peas [.25"] to pennies [.75"], no hail size will be indicated in the “Hazard” row nor will a description of damage risk be included in the “Impact” section.)

Wind – indicates estimated speed (in miles per hour) of wind gusts produced by the parent thunderstorm (e.g., “WIND...70MPH”). When included, the “Impact” section of the warning text will describe potential damage impacts from the straight-line winds, varying in severity depending on wind strength (e.g., “Expect considerable tree damage. Wind damage is also likely to mobile homes, roofs, and outbuildings.”).

Severe thunderstorm warning

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Convective storm detection

Severe thunderstorm watch

Severe weather

Severe weather terminology (United States)

SKYWARN

Supercell

Bureau of Meteorology: Severe Thunderstorm Warnings

Meteorological Service of Canada

United States National Weather Service