Changes In Extreme Winter Wind Chill Temperature Across the U.S. and Canada

Wind chill temperature (WCT) corresponds to a person’s physiological response to a cold and/or windy environment and is derived from air temperature and wind speed. In addition to WCT providing important information for public safety during winter outdoor activity, it can give insight into changes in regional climate conditions over longer periods. In this study, 133 hourly surface weather stations were used to examine the spatiotemporal changes in winter extreme WCTs across the U.S. and Canada during 40 winters from 1979/1980-2018/2019. Extreme WCTs were defined as the coldest 1% of WCTs at each station using observations across the 40 winters. The most extreme WCTs were located in northern Canada, with the coldest occurring north of Hudson Bay in Coral Harbor, Nunavut, with a WCT of -57°C. Over most of the U.S. and Canada, extreme WCT warmed by 2-6°C from the winters of 1979/1980 to 2018-2019, with the most warming in Alaska, northern Canada, and the central and western United States. Generally, mean WCT and temperature followed similar trends, having changes as large as 1.6°C/decade and 1.2 °C/decade, respectively in Alaska. The similar temporal and spatial trends in mean WCT and temperature demonstrate that temperature plays a dominant role compared to wind speed for changes in mean WCT. Wind speeds generally slowed across most areas of the U.S. and Canada, and wind speeds reduced (by 0.8-1.2 km/hr/decade) over the Eastern U.S. and Central Alaska.