Thursday, February 21, 2013
Granville, North Dakota, recorded an 83-degree rise in temperature on this date in 1918, one of the most extreme temperature changes ever recorded. In only twelve hours, the temperature climbed from 33-degrees Fahrenheit below zero to 50-degrees above. The 83-degree swing was only one example of extreme temperature changes caused by a meteorological phenomenon known as ‘Chinook winds.’
Chinook winds occur when eastern-moving winds bump up against the Rocky Mountains. The winds lose moisture during the impact, usually resulting in snowfall on the western side of the mountain range. The lighter air then begins to move up and over the mountains, and will begin to descend rapidly down the eastern slope, heating up as they descend due to a process known as adiabatic heating. Once the fast-moving air reaches the arid central plains, it spreads out into a strong, warm wind, with the ability to rapidly vanquish winter temperatures and melt deep snowpack.
French explorers first noticed the phenomenon in the early 19th century, and named the winds after the Northwestern Chinook tribe. Ironically, the word ‘Chinook’ literally translates to ‘snow-eaters.’ First used to describe the Native American tribe that would eat snow during the winter months, it also characterizes the warm Chinook wind that melts snow and ice as it moves east across the plains. Although southern Alberta remains the area most susceptible to the Rocky Mountain Chinooks, the northern plains of Montana, Wyoming, and North and South Dakota are also affected by these warm air masses. In 1943, the temperature in Spearfish, South Dakota, rose 45-degrees in just two minutes, only to drop 58 degrees in 27 minutes a few hours later. During Chinook events, winds can reach up to 140 miles per hour, the same force experienced during a level 4 hurricane, and the air becomes so dry that it’s often possible to see static electricity in the air.
Chinooks are not confined to North America. The same weather pattern occurs under different names around the globe: in Poland, they are referred to as Halny Wiatr, and in Argentina, as Zonda winds. Whatever their name, most North Dakotans welcome the warm respites they sometimes offer during the cold winter months.
Dakota Datebook written by Jayme L. Job
Gladstone, Jack. 2010 “The Bear who Stole the Chinook,” in Trickster: Native American Tales, pp.
185-193. Fulcrum Books: Golden, CO.