The conversation at the coffee shop this week turned to the weather, as it has every day for weeks now. Joe’s opinion was that the wind chill index commonly reported in news forecasts is nothing more than an “index of human misery” and really doesn't mean anything.
That aroused my curiosity. Is the sole purpose of this widely reported index just a way to express how cold we feel? Or does it tell us more about our safety? What I learned surprised Joe.
The wind chill temperature index used by the National Weather Service and NOAA was actually designed as a joint effort with several agencies in Canada, revised in 2001, and is now used in both countries. Volunteers were actually tested in wind tunnels and treadmills with electronic sensors to measure skin temperature.
Not surprisingly, the researchers learned that as wind speed increases, you actually feel colder on your skin, because wind speeds up the loss of heat we naturally emit. The faster the wind speed, the faster our body heat is taken away and the colder you feel. It is the same principle as blowing on a spoon to cool your hot soup.
So the true effect of the wind is to reduce the amount of time it takes your skin to freeze. As an example, on January 28th, the South Bend Airport recorded a low temperature of -14 degrees F. At that temperature, with a calm 5 mile per hour wind, your skin freezes in 30 minutes. If the wind speed increases to 20 mph, skin can freeze in 10 minutes. At 45 mph, it would take only 5 minutes for exposed skin to freeze.
The take home message for farmers, construction workers, and anyone who ventures outside during the depths of a winter freeze is to take wind chill seriously. It is not simply telling you how cold you feel. The wind chill index is telling you how quickly you could be frostbitten. The National Weather Service maintains a website with a Wind Chill Chart and a wind chill calculator at http://www.nws.noaa.gov/om/windchill/
Jeff Burbrink is an Extension educator in agriculture and natural resources. Write to him at 17746 E. C.R. 34, Goshen, IN 46528; call 533-0554; or fax 533-0254.