What Is A Chinook Wind?

A Chinook wind is known as a Fohn wind, which is experienced in parts of North America, where the Canadian Prairies and Great Plains end and the mountains begin.  It can be experienced up to about 250 miles east of the Rocky mountains and beyond, although perhaps to a lesser degree.
A chinook starts off as a warm, moist wind which blows east from the Pacific.  As it passes over the Rocky Mountains the moisture falls as rain or snow.  Then as it crosses the Rockies, when it reaches the land the other side of the Rockies, it is very dry and warm.
It is often referred to as the 'Snow Eater' because it can substantially raise temperatures.  The greatest chinook which was ever recorded was in Loma, Montana, on January 15th 1972, when the temperature was raised from minus 47 degrees Celsius, to plus 9 degrees Celsius.  This is the most dramatic change in temperature over a 24 hour period which has ever been recorded.