Chinook Winds: The Snow Eater
Chinook is an Indian word that means, “snow-eater”. The chinook winds can be a nice warming wind bringing instant spring in the middle of winter or a howling destructive windstorm. Chinook winds can raise temperatures by 25 to 35 degrees in minutes, melt snow completely, sandblast cars, collapse buildings and blow trucks off of the road
Chinook winds are down slope winds and are most common just to the east of the Rocky Mountains, but also occur east of Sierra Nevada Mountains, the interior of Alaska and east of the Cascade Range in North America. These winds are caused by the same pressure differences that cause the Santa Ana winds of Southern California. In this case, the high-pressure area will be to the west of the Rocky Mountains and the winds blow down the eastern side. The wind travels downhill picking up speed as it goes. The chinook wind blowing down slope heats up by a process known as adiabatic heating or actually the dry adiabatic lapse rate. The heating of the air occurs at a rate of 5.5 degrees F per 1,000 feet (10 C per 1000 Meters). Or for every 180 feet downhill the temperature can increase by 1 degree F. Humidity also drops and can drop to as low as 10% and lower.
To the west of the continental divide, the air moves up mountains producing snow. There can be a snowstorm in Vail, Colorado and just to the east of the Continental Divide it can be warm and very windy. As the air moves up on the western slope of the mountains, it drops all its moisture. Then on the way down the eastern side of the Rocky Mountains it picks up speed and heats up as it blows down the mountains. When it hits the base of the foothills it spreads out as a strong chinook wind, warming and drying the air.
Wildfires aren’t so much a danger with the chinook winds as with the Santa Ana winds since they usually occur in winter with snow cover on the ground. The chinook winds can be much more powerful than the Santa Ana winds reaching over 100 mph with numerous instances of the winds blowing over 140 mph (225 kph) at cities like Boulder, Colorado and Livingston, Montana. That would be the same as a category 4 hurricane. The main threat from the chinook wind is the damage to buildings and cars. It is not unusual for cars to be sandblasted or having their windows blown out while driving on the Boulder Turnpike between Denver and Boulder during a chinook windstorm.
Since the Rocky Mountains are so much higher than the Santa Ana Mountains, the jet stream can actually influence the strength of a chinook windstorm. This also causes the air and the clouds to stay almost stationary over the mountains. These stationary clouds over the mountains create what are called standing wave clouds or lenticular clouds. These clouds are called lenticular because they are shaped into clouds that look like lenses and can be absolutely beautiful. They have also been called flying saucer clouds since they can resemble a flying saucer.
The chinook winds have caused some amazing temperature changes. Temperature rises of 27 to 36 F (15 to 20 C) are common during a chinook windstorm. The Black Hills of South Dakota, just east of the Rocky Mountains also has chinook winds. A world record temperature rise occurred in Spearfish, South Dakota on January 22, 1943 when the temperature went from –4 degrees F (-20 C) to 49 degrees F (10 C) in just three minutes. I have seen the temperature rise from a bitter –20 F to 32 F in an hour and over a foot of snow melt in just one day.
The chinook winds cause the air to become so dry, you can see the static electricity arcing when touching a doorknob. And be careful touching your dog’s wet nose during these dry chinook windstorms.
These dry chinook winds can also have a negative affect on how you feel and your health. The chinook winds create positive ions, and positive ions put people in a bad mood, police departments always report an increase in violence during these dry winds.
Chinook winds are called by different names in other parts of the world. In the Swiss Alps they are called the Foehn, Zonda in Argentina, Halny Wiatr in Poland and in Java they are called koembang.
© 2009 Sam Montana