The Wind Chill Factor
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The wind chill factor (or wind chill index) is a number, often
expressed as an equivalent temperature, that expresses the cooling effect of moving air at
different temperatures. The lower the windchill, the more calories of heat are being
carried away from the exposed surface of the body. The concept was originally developed in
1939 by Paul A. Sipel, an Anarctic explorer and an expert on cold climate issues. Many of
the experiments originally conducted measured the time it took a small container of water
to freeze as a function of air temperature and wind speed. Other factors such as sunshine,
your own metabolism, and of course protective clothing, will determine how cold you feel
outside. The windchill is a useful guide to quantify the impact of the two major factors
(air temperature and air motion) on your bare skin. There is increasing discomfort but
little danger of frostbite for properly clothed persons down to about -20 degrees F
windchill. Between -20 and -70 degrees F, danger of frostbite increases rapidly unless
special precautions are taken. Below -70 F degrees, exposed skin can freeze within 30
seconds and Arctic survival gear is an absolute must. And keep in mind, skiers and
snowmobilers create their own wind. Cruising through the woods on a calm zero degree day,
riding a snowmobile at 25 mph, exposes the passengers to a -24 degree F windchill.
Sources:
The Handy Weather Answer Book, Visible Ink, Detroit, 1997
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