I found the following at http://weather.miningco.com/science/weather/library/weekly/aa120198.htm:Calculating Windchill
The National Weather Service uses the following formula to calculate the windchill:
Windchill Temp. (§F) = 0.0817(3.71(V)^0.5 + 5.81 - 0.25V)(T - 91.4) + 91.4
where V is the wind speed in miles per hour and T is the outside temperature in degrees Fahrenheit.
In SI units, the windchill is calculated using the following formula:
Windchill Temp. (§C) = 0.045(5.27(V)^0.5 + 10.45 - 0.28V)(T - 33.0) + 33.0
where V is the wind speed in kilometers per hour, and T is the outside temperature in degrees Celsius.
To simplify the calculations using the formulas above, the windchill temperature can be determined using the calculator below (you'll have to go to that site for this, as it didn't copy correctly.) After you enter a new wind speed or temperature, tab or click outside the box and the windchill temperature will be automatically updated.
Temp (§C)If you deplore calculations and want the information tabulated, USA Today provides an excellent reference table. Find your wind speed on the vertical axis, air temperature on horizontal axis, and follow the column and row until intersection to determine your windchill temperature.
If you live in the United States, you can look for your state and associated windchill at the Ohio State or Weather Underground windchill graphics site.
Limitations to Windchill
Various scientists around the world have presented issues and concerns regarding the validity of the windchill calculation. These issues include the complexity of interaction between the wind and people, measurement heights of wind speed, clothing insulators, and sunshine warming effects. These issues are well founded and worth considering when performing calculations and analyzing windchill.
Quiz Time
Do you think you fully understand the concepts discussed above? Try the quiz below to test your knowledge. Jot your answers down on a piece of scratch paper and check them after your have completed the quiz.
Q1 Skiing down your favorite winter slope, you view a thermometer reading 20§F. At 12 miles per hour, what is the effective temperature on your face (the only uncovered part of your body)? Feel free to use the calculator above.
Q2 If the outside temperature is 5§C, the wind speed is 15 kilometers per hour, and you place a glass of water outside, will the water freeze?
Q3 At 0§C and no wind, what is the windchill temperature and why is it different than the reading on the thermometer?
Q4 You recently replaced the antifreeze in your car because the TV weather forecaster predicted winter windchill temperatures dropping into the 10s (degrees F) and ambient air temperatures in the 20s. Your old antifreeze was rated to 20§F, while the new antifreeze is rated to 10§F. Assuming that the old antifreeze was still good, was the change necessary?
(Answers are at a link at that website.)