Severe thunderstorm warning

A severe thunderstorm warning (SAME code: SVR) is an alert issued when trained storm spotters or a Doppler weather radar indicate that a thunderstorm is producing or will soon produce dangerously large hail or high winds, capable of causing significant damage. In the United States, severe thunderstorm warnings do not account for lightning, a significant hazard in any thunderstorm, or flooding caused by a thunderstorm's extreme rainfall (a flood advisory or Flash Flood Warning is issued in these cases). A similar warning is issued by Environment Canada's Meteorological Service of Canada from their offices in Vancouver, Edmonton, Toronto, Montreal and Dartmouth. Skywarn issues the severe thunderstorm warnings for the United Kingdom. Also, just as in the United States, lightning does not warrant a severe thunderstorm warning. In Australia, severe thunderstorm warnings are issued by the Bureau of Meteorology for all Australian states.

In the United States, the National Weather Service (NWS) defines a severe thunderstorm as having large hail of at least 1 inch (2.5 cm), surface wind speeds of 58 miles per hour (93 km/h) or greater, or both. Prior to January 2010, the hail size for which a thunderstorm would be considered severe was 0.75 inches (1.9 cm); public complacency due to overly frequent issuances of severe thunderstorm warnings and recent studies stating that hail did not produce significant damage on the ground until it reached one inch in diameter caused the upgrade in hail criteria.

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