Chinooks are warm and dry winds that descend the eastern slopes of the Rocky Mountains and dramatically affect the cold-season weather of the western Great Plains. This term is derived from the Chinook Indians of Oregon, who originally identified a local unseasonably warm wind as a "snow-eater." Air from a mild source region over the Pacific Ocean is further warmed by compression as it descends downslope and replaces a shallow cold air mass. Chinooks are capable of warming regions near the mountains by 50ºF to 68\F in time periods as brief as fifteen minutes, leading to a rapid melting of any snow cover that is present. Some of the greatest extremes of temperature change in U.S. history have occurred in the Great Plains due to chinooks, including a warming of 81ºF in two minutes in Spearfish, South Dakota, on January 22, 1943.
While chinooks have beneficial temperature effects during the cold season, they may also be accompanied by severe windstorms, especially east of the Front Range of the Colorado Rockies. A stable layer in the atmosphere just above the mountains and a low-pressure trough to the east of the mountains cause westerly winds to accelerate over the Front Range. In this situation, a mountain wave can develop that forces the air above the mountain upward followed by a severe downslope acceleration. In one instance, a chinook windstorm struck Boulder, Colorado, on January 17, 1982, with winds in excess of 200 feet per second, resulting in more than $17 million in damage.
See also FOLKWAYS: Chinook Stories.
Michael A. Palecki Midwestern Regional Climate Center
Barry, Roger G. Mountain Weather and Climate. New York: Methuen & Co., 1981.
Geer, I. A., ed. Glossary of Weather and Climate. Boston: American Meteorological Society, 1996.
Keen, R. A. Skywatch: The Western Weather Guide. Golden, CO: Fulcrum, Inc., 1987.