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Abstract Wind chill temperature (WCT) is a widely recognized biometeorological variable that quantifies atmospheric conditions that have consequential impacts on many aspects of society, especially human health through exposure to winter conditions that can result in hypothermia, frostbite, and cardiorespiratory mortality. The spatial and temporal variations in WCT and extreme WCT (E WCT) (coldest 1%) were examined using hourly surface measurements collected at 133 stations across Canada and the United States during 40 winters (1979/80–2018/19). Most locations experienced an overall warming in both mean and extreme WCTs. The most substantial and statistically significant warming of mean WCT occurred across Alaska and the Canadian Northwest Territories with values of +3.2° to +6.4°C during the 40-winter time period. Statistically significant warming of mean WCT also occurred along the East Coast of Canada and the United States, as well as across the southeastern United States. Extreme WCT was found to be 10°–30°C colder than the mean WCT, and generally, the extreme WCT warmed at a greater rate than the mean WCT at locations. For example, extreme WCT warmed as much as +10.4°C during the 40-winter time period across portions of Alaska and the Canadian Northwest Territories. Warming air temperatures were found to have a large relative contribution to warming of mean and extreme WCTs with a smaller contribution coming from decreasing wind speeds (WS).