Chinook Winds: What Are They?

Ever wonder why some mountains are extremely snowy on one side, yet completely dry on the other? This phenomena can be explained by the Chinook winds. 

The term “Chinook” originates from the Chinookians indigenous to the Pacific Northwest along the Columbia River. To European settlers, the “Chinook wind” meant a warming wind blowing off the Pacific Ocean into the interior western U.S. These winds are full of moisture and are associated with heavy rain and snowfall.

When the Chinook winds approach the mountain ranges of the western U.S. they are forced upwards in a process known as orographic lifting. As these moist air parcels are lifted to higher elevations, moisture quickly condenses out of the sky. On windward sides of mountain ranges, these winds can create very extreme precipitation events.

Once the winds reach the top of the mountain, they become extremely dry before beginning to travel downslope. This results in a “rain-shadow” effect. On the leeward side of the mountain, these dry air parcels warm up much quicker than their surroundings. Chinook winds often gain intensity as they reach lower elevations and can reach hurricane strength force. 

The reason Chinook winds warm up rapidly on the leeward mountain side is due to differences in the moist and dry adiabatic lapse rate. A lapse rate is an air parcel's change in temperature due to elevation. As the Chinook winds travel upwards, the wet air parcel cools at the moist adiabatic lapse rate which is approximately 6 degrees Celsius per kilometer. However, once the air parcel has lost all of its moisture and begins traveling to lower elevations, it warms at the dry adiabatic lapse rate which is 10 degrees Celsius per kilometer. Therefore, the air parcel heats up much faster than it originally cooled down. 

Rapid, extreme temperature changes have occurred as a result of the Chinook winds. In 1972, Loma, Montana experienced a 103 degree Fahrenheit temperature change in only 24 hours! Also, the Chinook winds contributed to Spearfish, South Dakota experiencing the fastest temperature increase in the world. 49 degrees Fahrenheit in 2 minutes! 

If residing in the western U.S. make sure to stay up to date on potential impacts the Chinook winds may have on your local forecast. 

Source: Chinook Winds, Wikipedia