What is the Wind Chill?
The Wind Chill Temperature Index, sometimes also known as the equivalent
temperature, is used to describe how cold people and animals feel when
they experience heat loss caused by the combined effects of low temperature
and wind.
When the wind blows across exposed skin, it removes the insulating layer
of warm air that lies adjacent to the skin. This in turn drives down the
skin temperature and eventually the internal body temperature. The faster
the wind blows, the faster the heat is carried away, the greater the heat
loss and the colder it feels.
A new Wind Chill Temperature Index took effect on November 1, 2001,
replacing the original wind chill index that was derived in 1945. The
original Wind Chill Index was developed by two Antarctic explorers and
was based on research involving the time it took water in a plastic
container to freeze. The new Wind Chill Temperature Index includes the
latest advances in science, technology and computer modeling. It takes
into account a calculated wind speed at average face height based on
readings from winds measured at the national standard height of 33 feet.
It is based on the exposure of a human face to cold versus a plastic
container, incorporates modern heat transfer theory, lowers the calm
wind threshold from 4 miles per hour to 3 miles per hour, and has a
consistent standard for skin tissue resistance. The new Wind Chill Temperature
Index currently assumes no impact from the sun, but it may yet be revised
again for solar radiation impacts under various sky conditions (clear,
partly sunny, cloudy). For additional information on the new Wind Chill
Temperature Index, please see http://www.nws.noaa.gov/om/windchill.
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