Ringing in the New Year with Wind Chill? (Photo Credits: The Weather Channel, National Weather Service)
Party goers waited in near zero wind chills as they watched the ball drop in Times Square on New Year’s Eve. Winds chills in Nashville fell below 0 degrees Fahrenheit, -10°F in D.C., Oklahoma City dropping to -12°F, Chicago at -25°F, North Dakota in the -30°F range, Boston remaining sub 20 degrees for several days in a row, and the Florida panhandle expecting freezing rain. Even Fairbanks, Alaska seemed warmer than the Midwest, Great Lakes, and Northeast with positive single digit wind chills amidst the blast of cold Arctic air.
But, what is wind chill exactly? Wind chill states how cold it “feels” when the wind is blowing. It was developed in the 1940's by two American scientists stationed in Antarctica that found wind speed and temperature to be the greatest factors in the freezing rates of a water bottle they had placed on the top of their hut. In reality, it measures the heat loss of exposed skin through convection. The rate of convection depends on the difference in the temperature of a surface and the fluid surrounding it. Moving air allows cooler air to be placed against a warm surface, increasing the rate of heat loss for faster wind speeds and reducing objects to the ambient temperature more quickly.
However, there are several assumptions that the wind chill equation makes. It assumes that it’s nighttime with clear skies and that you are in an open field, walking 3 mph straight into the wind, 5 feet tall, and feeling the wind against your bare skin. Wind chill also only uses average wind speed, not wind gusts. Most ASOS (Automated Surface Observing Systems) stations record wind speed and direction every 5 seconds and a 2-minute average of these speeds and directions are reported. The peak wind speed is the greatest 5-second average exceeding 25 knots (~28 mph) in the last hour. The reasoning behind using average wind speed in calculating wind chill is that it provides a more accurate representation of the body’s thermal equilibrium response.
Hypothermia can set in anytime it falls below 50°F and winds speeds greater than 3 mph, but affects people differently based on age and gender. Wind chills less than -35°F can cause frostbite in as little as 30 minutes. The best way to prepare for cold weather is to prepare your car with extra supplies, dress in layers, and only go out in the cold if you must.
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© 2018 Meteorologist Sharon Sullivan