How is wind chill calculated?
DB: This is Earth and Sky. Al Druckrey of Jacksonville, North Carolina wants to know how to calculate wind chill.
JB: He writes, “My kids ask and all I can tell them is they use a math formula.” Al, meteorologists do use a math formula – we’ll talk more about that just a moment.
DB: But first tell your kids that our bodies emit heat that normally stays in a thin envelope of warm air all around us. When the wind whisks away that warm layer, we lose heat faster – and that’s wind chill. The formula calculates the relationship between wind speed, air temperature and how cold you feel.
JB: The wind chill concept came from two Antarctic explorers, Paul Siple and Charles Passel, back in the 1940s. They hung a plastic bottle of water on a clothesline and measured how long the water took to freeze under different conditions. Their measurements served as the basis for the first wind chill equation used by the National Weather Service, beginning in 1973 . . .
DB: By 2000, better computers let a group of U.S. and Canadian scientists revise the equation – with the help of volunteers who walked through a wind tunnel with sensors on their bodies and faces. Both Canada and the U.S. began using the new – and far longer – equation a year ago.
JB: For web links to the equation, come to Today’s Show at earthsky.org. And with thanks to the National Science Foundation, we’re Block and Byrd for Earth and Sky.
Wind chill links:
To see a wind chill chart, try this link: www.nws.noaa.gov/om/windchill
For the less math phobic, the equations of the old and new wind chill indices can be found here (Meteorological Survey of Canada)
This site is good for background about wind chill:
National Climate Data Center (National Oceanic and Atmospheric Administration)
Here’s another good site for wind chill background:
National Weather Service (National Oceanic and Atmospheric Administration)
The following individuals were interviewed for today’s show. Our thanks to:
Mark Tew and Susan A. Weaver
NOAA
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