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Science File | I DIDN'T KNOW THAT

November 19, 2001

Last week's Q&A was truncated. Here is the full item:

Question: Why did the National Weather Service change how it calculates wind chill factor?

Answer: The wind chill factor was originally developed by researchers in the Antarctic as a way to measure the cooling effect of wind on exposed skin. But recent studies have indicated that the old formula gave too much importance to wind speed. The new formula was calculated by using six men and six women, ages 18 to 42, who were placed on a treadmill in a climate-controlled chamber and asked to walk for 90 minutes in temperatures as low as 14 degrees and winds as high as 18 mph. Electrodes inside their mouths and attached to their skin recorded heat loss, and a computer calculated the new formula:

W=35.74+0.6215T-35.75V0.16+0.42757V0.16, were W is the windchill in degrees Fahrenheit, T is the air temperature about 5 feet above the ground and V is the wind speed in mph. The formula is good only for air speeds above 3 mph. As an example of the change's effects, for a temperature of 35 degrees and winds of 20 mph, the new formula gives a wind chill of 24 degrees. With the old formula, it would have been 11 degrees. More information is available at: http://205.156.54.206/er/car/hang/windchill.htm.

FOR THE RECORD
Los Angeles Times Thursday December 20, 2001 Home Edition Part A Part A Page 2 A2 Desk 2 inches; 53 words Type of Material: Correction
Windchill formula--A formula for calculating windchill that appeared on the Nov. 19 science page was missing one term. The correct formula is: W=35.74+0.6215T- 35.75V0.16 +(0.42757T) (V0.16 ), where W is the windchill in degrees Fahrenheit, T is the air temperature about 5 feet above the ground and V is the wind speed in mph. The formula is good only for air speeds above 3 mph.
For the record
Los Angeles Times Monday December 24, 2001 Home Edition Part A Part A Page 14 Metro Desk 2 inches; 37 words Type of Material: Correction
In the Nov. 19 I Didn't Know That, a letter was left out of the formula for calculating windchill factor. The correct formula is: Windchill = 35.74 + 0.6215T -35.75(V0.16) + 0.4275T(V0.16), where T = air temperature, V= wind speed (mph) and windchill is in Fahrenheit.

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