A February Chinook

Raked by gusty southwest winds yesterday afternoon, the Front Range urban corridor enjoyed temperatures in the low to mid seventies (F); in Denver, an 86 year-old record high for the date (71F) was exceeded by two degrees.  It felt as if we had skipped late winter and early spring and had moved on to May.

In truth, such "chinook" events are common in this region and can occur during any month of the year, often mimicking a seasonal change in the course of a day.  Produced by high pressure west of the Front Range and low pressure over the High Plains, the intense, often damaging winds spill across the mountains, descending 5000 feet or more to the Colorado Piedmont.  As the air mass plummets, it compresses, heats up and dries out, bringing warm temperatures and low dew points to the urban corridor.  Any snow that might still coat the Piedmont rapidly vanishes (hence the mistaken belief that chinook means "snow-eater" when it actually refers to Native American tribes of the Pacific Northwest, a region from which the wind-producing storms often originate).

Generally short lived, the chinook winds are usually followed by a brief period of calm, mild weather.  However, depending on the movement of the storm system that produced them, winds may suddenly shift from a different direction and, if an upslope flow develops, winter chill and snow may return to the Front Range cities, changing the season once again.