December 5, 2002 at 3:24 AM EST - Updated June 15 at 11:56 PM
A New Wind Chill Index
By Meteorologists David Turley and Patrick Prokop
It’s the middle of winter and you have to go out and run some errands. You turn on the television to hear the weather forecast. You hear the Meteorologist say that it will be sunny and breezy with a high of 30 degrees but it will feel like 19 degrees. Does this mean that you should dress for 30 degrees or 19 degrees? The answer is 19 degrees. The reason is because of the wind chill.
Your body is always giving off heat, even in the summertime. On a cold day, with calm winds, the heat that escapes from your body will stay near your body and warm the air next to it. If it’s windy out, the wind will carry that warm air away from your body. As the winds blow faster, your body’s heat is escaping faster. The more heat that escapes, the colder you feel. This is why you feel colder when the wind blows.
The wind chill is a combination of the temperature and the velocity of the wind. For many years the National Weather Service used this equation: wc_old = 0.0817*(3.71*sqrt(ws_mph)+5.81 0.25 * ws_mph)*(tempf 91.4) + 91.4 +.5) to determine the wind chill. Starting in 2001, that equation has been changed. The new equation will be: wc_new = 35.74+0.6215*tempf 35.75*(ws_mph**(0.16)) + 0.4275*tempf*(ws_mph**(0.16)) This new equation is slightly different in that it gives warmer readings. For example, if the temperature outside is 30 degrees and the wind is blowing at 15 mph, the old wind chill would be 9 degrees. The new wind chill gives a warmer reading of 19 degrees.
In the above equations,: "ws_mph" is the wind velocity in miles per hour "tempf" is the temperature of theair in degrees Fahrenheit "vel**(0.16)" is the wind velocity raised to the 0.16 power. "sqrt(ws_mph)" is the square root of the wind speed in mph "*" means to multiply the two values.