Meet the “snow-eaters”

When I say the word “snow-eater” I immediately think of the classic admonition “don’t eat yellow snow” but have a hard time imagining the kind of creature it could be. Well, there’s in fact such a thing and it’s all “wind”. The name Chinook was given by the Chinook Indians to describe a warm winter wind that blows down the slopes of the mountains in western North America. Starting in Canada, these winds descend the Rocky Mountains in Alberta and in the United States down into the states of Montana, Wyoming, Colorado, South Dakota and Utah. These warm winds are not limited to the North American continent though; in the Alps they’re well known under the name of Foehn and you’ll also find them in the South American Andes where they’re called Zonda. Californians even have their own version of the phenomenon with the Santa Anna winds, notorious for causing terrible fires. As these winds descend a mountain slope, they get warmer and warmer as they drop and for people living in that area, this means a huge and swift increase in temperatures. Wind speeds also increase tremendously and can sometime reach hurricane forces. A few locals close to nature know a Chinook is approaching when they see an arch of wispy, white clouds following the mountain peaks as if they were glued in place. The clouds often look like ghost fingers dancing across the sky. How do these warm winds form? It’s a rain shadow wind which results from the subsequent adiabatic* warming of air which has dropped most of its moisture on windward slopes. As a consequence of the different adiabatic rates of moist and dry air, the air on the leeward slopes becomes warmer than equivalent elevations on the windward slopes. Chinook and Foehn winds can raise temperatures by as much as 54°F in just a matter of hours. Winds of this type are called "snow-eaters" for their ability to make snow melt - mostly through sublimation - quite rapidly. When snow was still a nuisance and not the "white gold" it's become these days, old folks from Haute-Savoie would say that ”one day of Foehn melts as much [snow] as 14 days of warm sunshine…” Because massive sublimation is involved, this is based not only on high temperature, but also on low relative humidity. To top it all, Chinook and Foehn winds are also said to have adverse effects on people’s health and behavior often causing headaches, anxiety and testiness. Within a few days, however, the warm sunny weather ends, winter weather returns, people get better and then complain about how cold and snowy it is once again. That I already knew; we’re all very hard to please…

* Temperature changing as we gain/lose altitude; the normal lapse rate of temperature averages 3 degrees Fahrenheit per 1,000 feet.