Read a wind-chill factor chart by plotting the ambient air temperature against the wind speed, resulting in the apparent temperature felt on exposed human skin. Generally, higher wind speeds at colder temperatures result in higher wind-chill factors, resulting in a colder subjective temperature.
The wind-chill temperature is derived from the formula of three added and one subtracted factors, using two variables for air temperature in degrees Fahrenheit and wind speed in miles per hour. The first added factor is the constant 35.74. The second is the product of the air temperature multiplied by 0.6215. The third is the product of the windspeed raised to the 0.16 power, the air temperature and 0.4275. Subtract the product of the windspeed raised to the 0.16 power multiplied by 35.75 from the three added factor.
The wind-chill chart provided by the National Weather Service, a division of the National Oceanic and Atmospheric Administration, features air temperatures ranging from 40 to minus 45 degrees Fahrenheit along one axis and wind speeds from 5 to 60 miles per hour on the other. A 5-mile per hour airspeed at 40 degrees yields an apparent wind-chill temperature of 36 degrees. Conversely, with air temperature of minus 5 degrees with a 10 mile per hour wind causes a minus 22 degree wind-chill temperature, which can cause frostbite on exposed skin within 30 minutes.