On the cold and windy days of last week, you probably tried to keep yourself warm by wearing appropriate clothing and seeking shelter from the wind.
It feels colder in the wind because the wind sweeps away heated air in contact with your body and replaces it with colder air.
Whereas still air is a poor heat conductor (which is why storm windows have air trapped between glass panes), moving air is not!
The cooling power of the wind is measured by the wind chill factor. The wind chill describes the increased loss of heat by the movement of the air. The wind chill is relevant to humans and other animals needing to maintain a constant temperature that is higher than the surroundings.
The wind chill factor cannot be measured with a thermometer; it must be computed. The wind chill temperature translates your body’s heat losses under the current temperature and wind conditions into the air temperature with a 3-knot wind that would produce equivalent heat losses.
This is not an easy conversion. The original wind chill formula was devised by Antarctic explorer Paul Siple in 1945. More recent research has revealed some flaws in Siple’s work, such as assuming that the wind at face level is equal to the wind at 33 feet above the surface. The National Weather Service updated its wind chill temperature calculation in November 2001.
Dr. Ed Hopkins, Wisconsin’s assistant state climatologist, has computed the wind chill temperatures for all the hourly temperature and wind speed combinations available from Truax/Dane County Regional airport since January 1948. Madison’s lowest wind chill temperature was -54.3 at 4 a.m. and 5 a.m. on January 20, 1985 — the same day of President Ronald Reagan’s second inauguration, which was held indoors because of the cold Washington, D.C., weather and because it was a Sunday. In the cold air outbreak of last week, the coldest wind chill temperature was -43 at 9 a.m. on Jan. 6.
