Climatology of Blizzards in the Conterminous United States, 1959–2000

Abstract

A blizzard is defined by the U.S. National Weather Service as winds over 16 m s?1 and falling or blowing snow causing visibility less than 400 m lasting for at least 3 h. Blizzard occurrence by county was tallied from Storm Data for the 41 winters from 1959/60 to 1999/2000. This revealed 438 blizzards for an annual average of 10.7, ranging from 1 blizzard in 1980/81 to 27 blizzards in 1996/97. The average area affected per blizzard was 150 492 km2 and the average number of people in affected counties was 2 462 949 per blizzard. There was a significant linear increase in the number of blizzards but no linear trend in the total area affected by blizzards or the population in affected counties during the period. Blizzards were most common in a ?blizzard zone? of North Dakota, South Dakota, and western Minnesota where each county had 41 or more blizzards in these 41 winters and the annual probability of a blizzard in each county exceeded 50%. Monthly occurrence of blizzards peaked during January in most areas, but during December in the Sierra Nevada, during March in the central Great Plains, and during April in Montana. There was weak correlation between the ENSO phase and the number of blizzards, with a tendency for more blizzards during La Niña and fewer during El Niño.