A Chinook wind can be a nice warming wind bringing instant spring in the middle of winter or they can turn into a howling destructive windstorm. Chinook winds can raise temperatures by 25 to 35 degrees in minutes, melt a foot of snow, and destroy property, sandblast cars, and blow trucks off of the road
Chinook is an Indian word that means “snow-eater”, which is exactly what they can do.
Chinook winds are down slope winds and are most common on the east facing slopes 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.
Why Chinook Winds are Warm
With Chinook winds, a high-pressure area will be to the west of the Rocky Mountains causing the winds blow down the eastern side to lower barometric pressure. The wind travels downhill picking up speed and heats the air as it goes.
As the Chinook wind blows downhill, the air heats up by a process known as adiabatic heating or more accurately 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). For every 180 feet downhill the temperature can increase by 1°F and as the air warms, the humidity also drops.
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 as much a danger with 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.
Chinook Winds - The Snow Eater Wind
- The greatest 24-hour temperature change occurred on January 14-15, 1972, in Loma, Montana when the temperature rose 103 degrees in 24 hours from -54°F to 49°F.
- On January 11, 1980, a temperature rise of 47° in seven minutes occurred in Great Falls, Montana.
The Black Hills of South Dakota, just east of the Rocky Mountains also have Chinook winds and wild temperature changes.
A world record for the most rapid temperature rise occurred in Spearfish, South Dakota, when on January 22, 1943, the temperature went from –4 degrees F (-20 C) to 49 degrees F (10 C) in just three minutes.
In Colorado, I have seen the temperature go from a bitter –25° for the morning low to an afternoon high in the mid 40s because of Chinook winds.
The Chinook wind 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. 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 and Lenticular Clouds
 |
| Lenticular clouds in N.M. / Brandy Jenkins CC BY 2.5 |
These stationary clouds over the 14,000-foot mountain peaks create what are called standing wave clouds or lenticular clouds.
Their official cloud name is Altocumulus Standing Lenticular. 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.
Lenticular clouds can stay over one area for hours or most of the day. There can be a single Lenticular, or stacked lenticular clouds on top of each other.
Chinook winds also cause what are called Chinook arch clouds or mountain wave clouds. These clouds are stationary and usually hang over the area just east of the Rocky Mountains all day and always seem to move east during the late afternoon, causing beautiful sunsets.
 |
| Chinook arch or mountain wave cloud at sunset |
© 2009-2019 Sam Montana
One thing about chinook winds that makes them so interesting is the abnormally high absolute winter maxima and uniquely large winter temperature ranges that occur in the chinook belt, which I define as extending from West Texas to Interior Alaska along the eastern and northern slopes.
ReplyDeleteNo place so far from the equator has seen a mid-winter temperature so high as 79 degrees Fahrenheit (26.1 degrees Celsius) as was recorded in Spearfish, South Dakota in January 1921. In the southern extremity of the chinook belt, temperatures reached 90 degrees Fahrenheit in February 1954, 1963, 1995 and 2017.
In December 1934, Fairbanks, a city so cold as to be in the widespread permafrost zone, had five consecutive days of above 50 degrees Farenheit. Yet in January that same year, the mean temperature was minus 37 Fahrenheit, and in December 1917 the warmest Fairbanks reached was 11 below zero Fahrenheit!
Hi JPBenny, thank you for reading my articles and commenting. Chinooks are sure interesting. Living here on the front range of Colorado my whole life, I have sure seen a lot of chinook wind storms in my life. They are not as prevalent as they used to be though because Denver has grown so much.
DeleteAnd yes, The area of Rapid City, east of the Black Hills have sure seen their share of temperature extremes.