Meteorology: Understanding the Atmosphere            Ackerman and Knox


If you attend a football game on a cool autumn night and you have a choice of sitting on a wooden bench or a metal bench, you will probably pick the wooden bench. The benches will have the same temperature but the metal one will feel colder because it has a higher heat-conductivity, and takes heat away from your body faster. On a cold, windy day you try to keep yourself warm by seeking shelter from the wind. It feels colder in the wind because of heat transfer by conduction. While still air is a poor conductor, moving air is not!

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 that need to maintain a constant temperature that is higher than their surroundings. The wind-chill factor cannot be measured with a thermometer; it must be computed. The wind-chill equivalent temperature, expressed in degrees, 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.   

A new Wind Chill Temperature Index took effect on November 1, 2001. The original wind-chill was based on research involving the time it took water in a plastic container to freeze. The new wind-chill   temperature index takes into account a calculated wind speed at average face height based (not at the winds measured at the national standard height of 33 feet), the exposure of a human face to cold versus a plastic container, incorporates 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 does not consider exposure to the sun.)

This applet converts temperature (F) and wind-speed (mph) to a wind-chill temperature. You must hit the return key after entering each number.