Forecast: Cold with Wind Chill
It has been cold recently, and when wind is considered, on some days, it has felt really cold. I have a weather station at home which reports the temperature outside and as well as “wind chill” temperature. Ever wonder what exactly is “wind chill”?
Wind Chill Temperature (WCT), according to the National Weather Service, is the temperature it “feels” outside and is based on the rate of heat loss from exposed skin caused by the effects of wind and cold. As the wind increases, the body will cool at faster rates causing skin temperature to drop. It is important to know that Wind Chill does not impact inanimate objects like your car, or water pipes, or your front door because those items cannot cool below the actual air temperature.
Wind Chill Temperature is calculated based on science, technology, and computer modeling. WCT is based on: the human face, incorporates heat transfer theory, calls calm 3 mph wind, uses a standard for skin tissue resistance, and presumes no impact from the sun. The National Weather Service (NWS) and the Meteorological Service of Canada (MSC) issue extreme temperature forecasts, including wind chill warnings and advisories that are important for public safety.
A new WCT was implemented for the 2001/2002 winter season designed to more accurately simulate how cold air feels on human skin. According to National Oceanic and Atmospheric Administration (NOAA), the concept of a wind chill temperature was first introduced and calculated from experiments in the 1940’s by two Antarctic explorers, U.S. Army Major Paul Siple and geographer Charles Passel. They measured the cooling rate of water in a bucket hanging from a pole. Since water will freeze faster than flesh, it overestimated the chilling effect of wind.
The new WCT index is based on exposed skin measurements from human subjects. In 2001 human testing was conducted with 12 volunteers, 6 men and 6 women by a U.S.-Canadian governmental group. The volunteers were placed in a cold wind tunnel, with thermal instruments stuck to their faces while they walked on a treadmill, exposed to a variety of wind and temperatures. The resulting WCT index is used in Canada and the U.S. and is based on wind speed at 5 feet height (considered the average height of an adult human face), wind readings at a height of 33 feet, and based on average human face tissue resistance.
The new WCT chart is available at http://www.nws.noaa.gov/om/windchill/ and on this page. Be sure to take wind chill into consideration the next time you venture outside,especially on the lake,where there is no shelter from the wind.
Date published on web site:
01-08-2010
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