Where did all the snow go? Last week at this time, the Front Range was entirely blanketed in several inches of the white stuff. Today, it’s almost gone. Where did it go?
The Answer: Chinooks.
Chinooks are warm dry winds. They get their name from a Pacific Northwest Indian word for “snow eater,” because when the chinook blows, the snow goes. With gusts that blast up to 120 miles per hour, pushing the temperature up 40 degrees F in minutes, chinooks along the eastern side of the Rockies are the most violent in the world. You always suspected that, didn’t you?
What causes a chinook? Chinooks are cool air pushed down by the weight of a high pressure front above them. Squeezing the cool air warms it up, to become warm dry, air. In winter and spring, chinook winds often buffet the areas just east of the mountains from Canada all the way to Mexico.
At ground level, the now-warm dry air is no longer under pressure. Like any compressed gas, it expands when released, and rips along the surface at 50 to 120 miles per hour as a chinook, melting and evaporating snow as it goes. By definition, chinook winds are warm and dry, and they suck the moisture out of plants, soils and people as they blow.
When a chinook blows, look toward the mountains. A bank of smooth clouds often hangs above the highest peaks. This is known as a foehn wall; it is created as the cool, wet, air crosses the mountains and is then forced down by high air pressure above that causes the chinook as well.
As the cool wet air containing the foehn wall is pushed down, it is compressed by the air above it; as it is compressed, it heats; as it heats, the amount of water it can hold increases (dew point rises) and the foehn wall cloud evaporates.
Chinooks also have the odd habit of “bouncing” over the land. They swoop down, blast some poor place with hurricane-force winds and then bounce back up, totally skipping over a locale just a few miles down the road.
In California chinooks are called Santa Aña winds, and in Europe, foehn (German for “warm”, pronounced “phone”. Actually, I heard a native German-speaker pronounce this word and it was closer to the way Peter Sellers and Steve Martin did it in the “Pink Panther” movies: “fun” as in “Your fun is ringing.”).