By Marlene Affeld

People who have spent some time in Montana tell eerie tales of the warm winter winds. Have you ever experienced a chinook? If so, you surely remember the sudden change in the weather. A dismal, gray, snowy day and suddenly everything doesn’t look quite so bleak. A bit of sunshine breaks through the dark cloud cover and the day begins to brighten. A frigid cold day warms.

Chinook winds offer a welcomed respite from the long winter. In Montana, chinook winds are a fairly common climatic phenomenon that delight and amaze both weather experts and residents alike. It begins with the smallest whisper and grows as it whistles and dances down the valley.

At the turn of the century, the Calgary Herald wrote, “Those who have not the warm, invigorating Chinook winds of this country, cannot well comprehend what a blessing they are. The icy clutch of winter is lessened, the earth throws off its winding sheet of snow. Humanity ventures forth to inhale the balmy springlike air. Animated nature rejoices.”

“Chinook” derives its name from a word in the language of the Chehalis Indian Tribe. In their language it means “snow- eater.” Aptly named, a chinook wind can melt over a foot of snow in a single day and raise the temperature as much as 40 degrees in less than an hour. The snow melt is caused partly by warmer temps and partly by the evaporation caused by the dry wind. Scientists tell us that adiabatic warming of downward moving air produces the warm chinook winds. Chinook winds are most remarkable in winter when the warm winds contrast with the ambient cold air.

Moist weather patterns that originate off the Pacific coast cool as they climb the western slopes and rapidly warm as they drop down the eastern side of the mountain ranges. A chinook begins with a sudden change in wind direction, usually towards the west and a rapid, dramatic increase in wind speed.

Loma, Montana holds the United States record for the greatest recorded temperature change. On January 15, 1972 the temperature went from a nippy -56F to a balmy 49F in less than 24 hours. In a much smaller time frame, on January 11, 1980, the temperature at the Great Falls International Airport rose from -32F to 15F in seven minutes as warm, chinook winds eroded an Arctic airmass.

Chinook winds often produce hazardous fire conditions. The warm wind sucks the moisture from the air and any fires that may breakout are vigorously fanned. The infamous Santa Ana winds are just another name for a chinook. Chinook winds are also called cierzo or mistral winds.

Repeated or prolonged chinooks can be quite damaging to the ecosystem of the forest. The dehydration caused by the warmth of the chinook wind can be dramatic and trees lose their winter preparedness. The trees lose moisture through their needles and as the ground remains frozen, there is no fresh water to replace that lost through dehydration. Often the needles will then turn brown and die. This condition is referred to as Red Belt. It is not a disease but a reflection of a severe lack of moisture within the needles. White Birch, like many other trees, cannot survive rapid temperature changes and often die after a winter chinook. Often fruit trees and other vegetation will “awaken” and start to sprout tender buds that will be destroyed by the next frost. An early spring chinook may destroy a season’s crop.

Most chinook winds are accompanied by a wide band of flat clouds that hover at high altitudes. Although these high clouds seem to hold the promise of rain, they rarely bring a drop. Viewing these clouds is often a breathtaking experience for photographers and all those that appreciate the artistic displays provided by Mother Nature. During a chinook, sunrise and sunset are profoundly beautiful as the sky is painted vivid shades of fuchsia, orange, and red.

The early settlers called these deep winter warm spells “false springs” as the wild chinook wind will sometimes linger for several days and it is easy to deceive one’s self that spring is on its way. However, when the chinook wind recedes, winter is back with all its fury.

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