Chinook winds are a weather phenomenon we see quite often in southern Colorado. They are a warm and dry wind that are the result of how the wind interacts with our mountainous terrain.

For example, a warm moist air mass sets up west of the Rockies. The weather moves from west to east, so this air mass will have to travel over the mountains. As it moves up the slope, the air cools, and all the moisture is squeezed out, resulting in showers, storms and snow over the Western Slopes. By the time the air reaches the eastern side of the Rockies, it is much cooler and dry. 

The air still has to travel down the slopes. As it moves down in elevation, it has the opposite reaction to traveling upslope. It warms instead of cools. The air warms an average of about 5.5 degrees per 1,000 feet descent. This means air could start at 15 degrees at the top of the mountains and warm to nearly 60 degrees after an 8,000-feet drop. 

This wind is very dry, warm and fast. It can reach speeds of 80 mph. We can see a pretty dramatic warm up at the base of the mountains in southern Colorado, even when we have a moderate downslope flow. This can even start to warm up temperatures before sunrise! 

These winds are sometimes called “snow killers” because they get rid of snow so quickly. As the warm, dry wind passes over snowy ground, it sublimates, or vaporizes, the snow before it even has a chance to melt.