Canada's Chinook Belt

The chinook is the best example of the family of mountain winds that blows in regions where long mountain chains lie more or less at right angles to the prevailing wind. Apart from the unseasonable warmth it brings to Canada's interior in winter, it represents an efficient system through which latent heat drawn from the Pacific coast is converted into sensible heat and transported zonally across the continent. It also compromises both the physical and human environments. The severity of impacts depends on either the amount of anomalous warming experienced or on the number of chinook events occurring over a winter, and often on both. In Canada, the chinook belt lies almost exclusively in southern Alberta. In this paper, the belt is described and mapped with respect to the strength of the wind's temperature signal and numerical frequency. The temperature signal (the signal) is the difference between the highest temperature attained during a chinook event and the daily maximum. The frequency is the number of days in the winter with, at least, 1 h of chinook wind. Mean point values of the signal range from 13 to 25 K. Mean seasonal frequency varies from 43 days to 52 days per winter. The core of the belt for temperature and frequency do not coincide. The highest frequencies occur in the Crowsnest Pass area whereas the strongest signals are found further east of the mountains in an axis that includes Vauxhall and Brooks. Both signal strengths and frequency show strong decadal variations. The 1980s were chinook rich; the 1970s were chinook poor.