Blizzard

Wednesday, October 22, 2008

A blizzard is a harsh winter storm condition characterized by low temperatures, strong winds, and heavy blowing snow. Blizzards are formed when a high pressure system interacts with a low pressure system. This results in the advection of air from the high pressure zone into the low pressure area. The term blizzard is sometimes misused by news media to describe a large winter storm that does not actually satisfy official blizzard criteria.

A winter storm must have winds of 30 mph or more, have snow or blowing snow, visibility less than 1 mile, a wind chill of less than −25 °C (−13 °F), and that all of these conditions must last for 4 hours or more before the storm can be properly called a blizzard. In North America, blizzards are particularly common to the extreme portions of the Northeastern United States, the Northern Great Plains in the United States, Atlantic Canada, and the Canadian Prairie Provinces. Blizzard conditions also occur frequently in the mountain ranges in western North America, however since these regions are sparsely populated they are often not reported.