A chinookis a warm, dry wind that arrives from the west after crossing the Rocky Mountains, and it is the reason Calgary's winter temperatures are so volatile. A chinook can lift the temperature by twenty degrees or more within a day, turning a deep freeze into a melt and back again within the same week. Calgary gets more of them than almost anywhere else in Canada.
Air moving in off the Pacific is forced up the western slope of the Rockies. As it rises it cools, and it drops most of its moisture as rain or snow on the British Columbia side. Having lost that moisture, it is a much drier parcel of air by the time it crests the divide — and dry air warms faster on the way down than moist air cools on the way up. It arrives on the Alberta side compressed and considerably warmer than it started.
The visual signature is the chinook arch: a long band of cloud along the western horizon with a strip of clear sky beneath it. If you can see the arch from Calgary, the warm-up is usually already on its way.
The west side leads. Higher, more exposed districts like Signal Hill — and Cochrane further west, where the Bow valley opens out of the foothills — register the warmth and the wind before the rest of the region. East Calgary is typically last, and on a strong chinook afternoon the temperature difference across the city can be several degrees. That gap is one of the clearest cases for a per-neighbourhood forecast rather than a city-wide one.
Chinooks are not purely good news. The wind is the main complaint — gusts strong enough to make driving on exposed routes unpleasant and to take down fences and shingles. The rapid thaw-and-refreeze cycle turns melted snow into sheet ice on sidewalks and side streets overnight, which is a bigger injury risk than the cold was. Many people also report headaches or joint pain during the sharp pressure change, an effect widely enough experienced here to have its own local nickname.
For gardeners and homeowners, the repeated freeze-thaw is harder on plants and on concrete than a steady cold winter would be.
Watch for the arch on the western horizon, a sharp rise in wind from the west or southwest, and a falling then rapidly rising temperature. On this site, the quickest tell is comparing the west-side districts against the east side on the live map — when Cochrane and Signal Hill run well ahead of Forest Lawn, a chinook is working its way across the city.