Wind-chill index

From Glossary of Meteorology
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wind-chill index

A means of quantifying the threat of rapid cooling during breezy or windy conditions that may result in hypothermia in cold conditions.

The index is used to remind the public to minimize exposure when outdoors and to take precautionary actions. In the late 1940s, Antarctic explorers Siple and Passel experimented with measuring the time it took to freeze 250 grams of water in different temperature and wind conditions. They developed empirical formulas relating these data to the rate of heat loss from exposed human skin. They developed the following formula which was used to determine the wind-chill index. At wind speeds of 4 mph or less, the wind chill temperature is the same as the actual air temperature:
where V is wind speed in mph and T is temperature in °F.