The chinook is a warm, dry wind that descends the eastern slopes of the Rocky Mountains in North America, from Alberta (Canada) to Colorado (USA). It is the North American equivalent of the Alpine Fohn effect: moist Pacific air rises on the western slope, cools, loses its moisture as precipitation, and descends on the eastern side warming adiabatically at roughly 10 °C per 1,000 m.
Extreme thermal effects
Chinooks produce some of the most abrupt temperature changes ever recorded on Earth. The most famous case occurred in Spearfish, South Dakota, on 22 January 1943: the temperature rose from -20 °C to +7 °C in just 2 minutes. In Calgary, Alberta, chinooks routinely raise temperatures 20-30 °C in a few hours during winter, melting snow with astonishing speed.
The name comes from the Chinook people of the Pacific Northwest. Native peoples called it "the snow eater" for its ability to melt thick snow cover in hours through the combination of heat, dryness, and wind. The very low humidity (often below 10 %) accelerates direct sublimation of snow.
Chinooks have significant implications for agriculture (they can save crops from winter cold but also cause damaging freeze-thaw cycles), health (they are associated with migraines and mood changes), and fire risk. The Argentine equivalent is the zonda. See also: Fohn effect.