Snow fell on Calgary, Alberta, on Monday after Sunday’s weather had been warm enough for sandals and shorts. But Calgarians are used to abrupt changes in the weather due to their location in the shadow of the Canadian Rockies.
Then it snowed again Tuesday and again Wednesday. The heavy, wet snow broke power lines and toppled trees. Schools and airline flights were delayed. And although it is unusual to get so much snow in Calgary in early September, it can be easily explained.
The city of Calgary is located just east of the Canadian Rockies. West of Calgary, mountains soar, whereas east of Calgary, the land slopes downward to the north and east.
Much of eastern Montana as well as the Rapid City, S.D., region have this same setup. Any time there is a moist, northeast wind, the air is cooled dramatically by being lifted (by the slope) to a higher elevation, causing rain to turn to snow. A dry, southwest wind has the opposite effect, causing unusually warm, dry weather.
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