Applied Heat Transfer in the Development of the New Wind Chill Temperature Chart

Abstract

In November, 2001, the national weather services of the United States and Canada, recognizing inaccuracies in the original, adopted a revised Wind Chill Temperature (WCT) chart. This revision was developed by the authors under a mandate from a joint action group for temperature indicies (JAG/TI) formed by the U.S. Office of the Federal Coordinator for Meteorology. This new chart provides, for a given air temperature and recorded wind speed, that air temperature, the WCT, which would result in the same rate of heat loss from exposed human skin in still air. Values of the WCT are given for a range of air temperatures from −45°F to 40°F and a range of wind speeds from 5 mph to 60 mph. For Canada, the ranges are from −50°C to 10°C and 10 km/hr to 80 km/hr. The new chart was developed using principles of heat transfer, including conduction, forced convection and radiation. Skin tissue resistance was obtained from human studies. This paper describes the application of these principles and will show how these same principles have been used to demonstrate the errors in the original chart developed over 60 years ago by our military in Antarctica and adopted by the U.S. Weather Service in 1973. As was the case for the original chart, a clear night sky has been assumed, thus ignoring any direct solar radiation that would otherwise tend to elevate the WCT. The new chart is unlikely to be the final version long term and this paper will also discuss possible future modifications.