Chinook winds are strong, warm, dry winds that blow down the eastern slopes of the Rocky Mountains. They occur when moist air is forced up and over the mountains, cooling as it rises and losing moisture along the way. These winds are best known for their ability to bring sudden variances in temperature. In places like Montana, Wyoming, and South Dakota, Chinook winds can cause temperatures to jump dozens of degrees in just a few hours, melting snow, breaking up ice, and dramatically changing conditions on the ground. Loma, Montana, holds the world record for the most drastic 24-hour temperature change, skyrocketing 103º from -54º to 49º in January 1972. Spearfish, South Dakota, holds the world record for the fastest increase and decrease in temperature. On January 22, 1943, the temperature increased from −4 to 45 °F, a 49 °F change in temperature, in just 2 minutes.
