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 at least 4 inches (10 cm) to 7 inches (18 cm) or more of snow or 3 inches (7.6 cm) or more of snow with a large accumulation of ice is forecast. 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 2 inches (5.1 cm) in the southernmost areas. 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.

Usually, a large accumulation of ice alone with 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.