Winter Storm Warning

A winter storm warning (SAME code: WSW) is a statement made by the National Weather Service of the United States which means a winter storm is occurring or is about to occur in the area, usually within 36 hours. Generally, a Winter Storm Warning is issued if the following criteria, at least, are forecast: usually between 4 inches (10 cm) to 7 inches (18 cm) or more of snow or usually 3 inches (7.6 cm) or more of snow with a large accumulation of ice. In the Southern United States, where severe winter weather is much less common and any snow is a more significant event, warning criteria are lower, as low as 1 inch (2.5 cm) in the southernmost areas. (Thus, as you go from south to north the necessary accumulations get higher.) A warning can also be issued during high impact events of lesser amounts, usually early or very late in the season when trees have leaves and damage can result. Winter Storm Warnings are issued when winds are less than 35mph; if the storm has winds above this wind speed, it becomes a blizzard warning.

Usually, a large accumulation of ice alone with little to no snow will result in an ice storm warning, or in the case of light freezing rain, a winter weather advisory, a freezing rain advisory, or drizzle advisory.

A similar warning is issued by Environment Canada's Meteorological Service of Canada from their offices.

Prior to the 2008–09 winter storm season, there was the heavy snow warning, specific for when only a heavy amount of snow was expected in the warned area. The Winter Storm Warning for Heavy Snow has since replaced it.

Because of the changes with the 2008–09 winter storm season, several varieties have been noted throughout the US:

Additionally, all of the above may also include "Strong Winds" in their title if strong winds are expected as well (e.g. winter storm warning for heavy wet snow and strong winds).

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