CELPIP Reading Part 3 Practice Test: Chinook Winds of Southern Alberta

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For people living in Calgary and across southern Alberta, few weather events are as welcome in the middle of winter as a chinook. These warm, dry winds sweep down the eastern slopes of the Rocky Mountains, sometimes turning a bitterly cold morning into a mild afternoon. It is not unusual for temperatures to climb by twenty degrees or more within a few hours, and residents may trade their parkas for light jackets before the day is out. The wind takes its name from the Chinook people of the Pacific Northwest, and it has also earned the nickname “snow eater” for the speed at which it can make snow vanish.

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The science behind a chinook begins over the Pacific Ocean. Moist air carried inland by westerly winds is forced upward when it meets the mountain ranges of British Columbia. As the air rises, it cools, and much of its moisture falls as rain or snow on the western slopes. Losing that moisture is only part of the explanation, however. The main reason for the warmth is what happens as the now-dry air descends the eastern slopes: it is squeezed by the increasing pressure around it, and this compression heats it quickly. Because dry air warms faster on the way down than moist air cools on the way up, the wind that reaches the foothills is noticeably warmer than when it began its climb. Similar winds blow in other mountain regions of the world; in the Alps, for example, they are known as the foehn.

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Long before the wind itself arrives, many Albertans can tell that a chinook is on its way simply by looking west. A broad band of clear blue sky often opens above the mountains, bordered by a sharp edge of cloud. This feature, known as the chinook arch, can stretch across the horizon and produces striking sunrises and sunsets that photographers eagerly wait for. Once the wind arrives, its effect on the snow can be dramatic. In such dry air, some of the snow does not simply melt but turns directly into water vapour, a process called sublimation, leaving bare lawns where deep drifts stood the day before.

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Not everyone welcomes the sudden change. Gusts during a chinook can be strong enough to make driving a high-sided truck on open highways dangerous, and the rapid swings between freezing and thawing help create potholes and icy sidewalks once the cold returns. Trees suffer too. Evergreens lose moisture through their needles in the warm, dry wind while their roots sit in frozen ground, and whole hillsides of them can turn reddish-brown, a sight known as “red belt.” Some residents blame chinooks for their headaches, and researchers in Calgary have found that certain migraine sufferers do report more attacks around chinook days. Even so, most people in the region would agree that a break from the deep cold is worth a few drawbacks.