Wind chill

How cold is it outside? Simply knowing the temperature will not tell you enough about conditions outside to enable you to dress sensibly for all winter weather conditions, since the speed of the wind also has an effect. For example, if the temperature is 5 degrees above freezing and the wind is blowing at 15 miles per hour (25 kilometers per hour), the cooling effect on your body is equivalent to the temperature of -25 degrees F (-32 degrees C) in still air. Exposed flesh quickly freezes under such conditions, since the combined effect of the wind and the temperature determines the rate at which your body loses heat.

This combined effect is commonly called the "wind chill factor" or the "wind chill index." The table on this page shows that the wind chill factor increases with the wind speed, up to a wind speed of 40 miles per hour (67 kilometers per hour). Above velocities of 40 miles per hour, any increase in wind speed has little additional effect on the body's loss of heat. The wind chill table can serve as a useful guide in determining how much protective clothing to wear for winter activities. The equivalent temperatures given on the table are valid only if you are wearing dry clothing; if your clothing is wet, evaporation of that moisture will greatly increase the chill factor.

To use the chart, find the approximate temperature on the left-hand side of the chart. Read across from the temperature reading and down from the wind velocity reading. The number which appears at that intersection is the equivalent temperature determined by the wind chill factor.

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Edited by Rene Munoz, munoz@ucar.edu