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A chinook is a warm, dry wind that blows down the eastern side of the Rocky Mountains from New Mexico to Canada. Chinooks occur in winter or early spring and bring a noticeable rise in temperature to the plains just east of the Rocky Mountains.
The chinook is classified as a katabatic wind. A katabatic wind is a strong, downhill wind that forms as cold, dense, surface air travels down a mountainside and sinks into the valley. The air is dried and heated as it streams down the slope. Sometimes the falling air becomes warmer than the air it displaces below.
"Chinook" is an Arapaho Indian word meaning "snow eater." This wind is so-named because it brings a dramatic warming to cold regions, melting the snow in its path. Chinooks can raise the temperature of an area by more than 36° Fahrenheit (20° Celsius) in just one hour and by as much as 60° Fahrenheit (15° Celsius) in one day.
Another type of warm katabatic wind is the Santa Ana, which brings warm, dry conditions—conditions ripe for forest fires—to southern California.
Sources: Bair, Frank E. The Weather Almanac, 6th ed., p. 280-81; Eagleman, J. R. Severe and Unusual Weather, pp. 50-52; Engelbert, Phillis. The Complete Weather Resource, vol. 1, pp. 128-30; Ludlum, David M. The Audubon Society Field Guide to North American Weather, p. 630.
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