A Chinook is a warm, dry wind that descends the eastern slopes of the Rocky Mountains in North America. It occurs when moist air rises over the mountains, cools, and loses moisture as snow or rain. As the air descends, it warms up, leading to a rapid increase in temperature, often melting snow and creating a sudden change in weather. Chinook winds can raise temperatures by as much as 20 to 30 degrees Fahrenheit in just a few hours. This phenomenon is particularly common in areas like Montana and Colorado, where residents often experience dramatic weather shifts during winter months.