Calculating wind chills, which method works for you?
There are differring ways to compute a wind chill.
Some of you may have heard of the old way to calculate wind chill as being roughly one MPH of wind as being a one degree drop in “feels like” air temperature during the winter.
For example, this was downloaded from the web last year:
The windchill factor is the temperature that a person feels because of the wind. For example, if a thermometer reads 35 degrees Fahrenheit outside and the wind is blowing at 25 miles per hour (mph), the windchill factor causes it to feel like it is 8 degrees F. In other words, your 98-degree body loses heat as though it is 8 degrees outside.
The windchill factor is the same effect that causes you to blow on hot soup to cool it down. The movement of the air increases the soup's loss of heat by convection, so the soup cools down faster.
For an inanimate object, windchill has an effect if the object is warm. For example, say that you fill two glasses with the same amount of 100-degree water. You put one glass in your refrigerator, which is at 35 degrees, and one outside, where it is 35 degrees and the wind is blowing at 25 mph (so the windchill makes it feel like 8 degrees). The glass outside will get cold quicker than the glass in the refrigerator because of the wind. However, the glass outside will not get colder than 35 degrees -- the air is 35 degrees whether it is moving or not. That is why the thermometer reads 35 degrees even though it feels like 8 degrees.
http://www.learner.org/interactives/weather/act_windchill/
Now look at the two methods below from the NWS to calculate wind chill, each of which are different from the above.
Found on USA Today.com
Formula used to calculate wind chill
The term "wind chill" goes back to the Antarctic explorer Paul Siple, who coined it in a 1939 dissertation, "Adaptation of the Explorer to the Climate of Antarctica." During the 1940s, Siple and Charles Passel conducted experiments on the time needed to freeze water in a plastic cylinder that was exposed to the elements. They found that the time depended on how warm the water was, the outside temperature and the wind speed.
In the fall of 2001, the U.S. National Weather Service and the Canadian weather replaced the formulas with new ones (one for Fahrenheit temperatures and one for Celsius readings). The new formulas are based on greater scientific knowledge and on experiments that tested how fast the faces of volunteers cooled in a wind tunnel with various combinations of wind and temperature.
The new formula for winds in mph and Fahrenheit temperatures is:
Wind chill temperature = 35.74 + 0.6215T - 35.75V (**0.16) + 0.4275TV(**0.16)
In the formula, V is in the wind speed in statute miles per hour, and T is the temperature in degrees Fahrenheit.
Note: In the formula, ** means the following term is an exponent (i.e. 10**(0.5 ) means 10 to the 0.5 power, or the square root of V), - means to subtract, + means to add. A letter next to a number means to multiply that quantity represented by the letter by the number. The standard rules of algebra apply.
For reference, the old wind chill formula was:
T(wc) = 0.0817(3.71V**0.5 + 5.81 -0.25V)(T - 91.4) + 91.4
Source for both formulas: The National Weather Service
The foregoing was downloaded from: USATODAY.com
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