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Chinooks
 

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Winters in Calgary are occasionally moderated by chinooks , sudden warming winds that periodically sweep down the eastern flanks of the Rockies. Often heralded by a steely cloud band spreading from the mountains over the city, a chinook can raise the temperature by as much as 10A°C in a couple of hours and evaporate a foot of snow in a day. Chinooks are the result of a phenomenon that occurs on leeward slopes of mountains all over the world, but nowhere more dramatically than in the plains of southwestern Alberta. The effect has to do with the way prevailing westerly winds are forced to rise over the Rockies, expanding and cooling on the way up and compressing and warming up again on the way back down. On the way up the cooling air, laden with Pacific moisture, becomes saturated (ie clouds form) and drops rain and snow on the windward (western) side of the mountains. All this condensation releases latent heat, causing the rising air to cool more slowly than usual; but on the leeward descent the air, now relieved of much of its moisture, warms up at the normal rate. By the time it reaches Calgary it's both drier and warmer than it was to start with.

The name comes from the people that traditionally inhabited the area around the mouth of the Columbia River in Washington and Oregon, from where the winds seem to originate; the Chinook people also give us the name of the largest species of Pacific salmon


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