Wind Chill is the term used to describe the rate of heat loss on the human body resulting from the combined effect of low temperature and wind. It was developed by Siple and Passel (1941) and is based on physiological studies of the rate of heat loss for various combinations of ambient temperature and wind speed.

When the wind speed is 4 mph or less, the wind-chill temperature is equal to the ambient air temperature. When wind speeds increase, the wind-chill temperature becomes lower than the air temperature, which results in increased cold stress and discomfort associated with the wind. The effects of wind-chill depend strongly on the amount of clothing and other protection worn as well as on age, health, and body characteristics.

Wind-chill temperatures near or below 0 F indicate that there is a risk of frostbite or other injury to exposed flesh. The risk of hypothermia from being inadequately clothed also depends on the wind-chill temperature. While exposure to low wind chills can be life threatening to both humans and animals alike, the only effect that wind chill has on inanimate objects, such as vehicles, is that it shortens the time that it takes the object to cool to the actual air temperature (it cannot cool the object down below that temperature).

The following equation can be used if the wind speed in mph (V) and the temperature in degrees Fahrenheit (T) are known. (SQRT = square root):

TWC=91.4-((91.4-T)*(.478+(.301*SQRT(V))-.02*V))