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Let’s put a freeze on the Wind Chill Factor

jsimmons@charlotteobserver.com

You might have heard: It’s going to be cold in Charlotte.

It’s what people are talking about in our office and yours. The forecast is for unseasonably cold temperatures, brutally cold temperatures, so cold that weather people will quickly run out of adjectives trying to describe how godawful cold it is.

At some point, perhaps even before those adjectives lose their power to wow us, the weather people will resort to a different, brain-numbing phrase.

The Wind Chill Factor.

Wind chill is an overhyped, inaccurate measurement that serves one purpose: It lets us make bad weather seem spectacularly bad.

Otherwise, it has no real-world value. It doesn’t tell you how cold your skin is getting. Air temperature determines that. For example, if the air temperature is 37 degrees but the wind chill is 24, you are not in danger of getting frostbite. The air temp needs to be below freezing for that.

Likewise, it doesn’t tell us when our pipes will freeze. Wind can make things more frigid, which can accelerate the freezing of water, but air temperature is again the main factor. (Researchers at the University of Illinois have determined the pipe-freezing threshold is about 20 degrees. So make sure those outdoor faucets are covered tonight, Charlotte.)

Why even have a wind chill factor? The measurement was developed in 1945 by Antarctic explorers Paul Siple and Charles Passel, who put together an index that they felt would capture how cold we feel at various temperatures with wind blowing.

There is an actual formula for wind chill. It’s been tweaked some since 1945, but basically it assumes that it’s nighttime, your exposed face is about five feet off the ground, and you’re walking about 3 mph directly into the wind. If you’re standing next to a building, or in the sun, or at 2 in the afternoon, you’re feeling something different.

And even then, wind chill is essentially only a calculation of that moment - not a general calculation of temperature - because the wind doesn’t blow at a constant, steady rate. Yes, it’s colder on your skin when the wind blows, but that number just can’t be measured precisely.

Why, then, is it cited so often? As always, blame the media. The original wind chill index went largely ignored until the media got hold of it, specifically at the legendary Ice Bowl 1967 NFL championship game between Dallas and Green Bay in Green Bay. Temperatures that day were -13 degrees, but that didn’t sound nearly as legendary as a wind chill of -48.

So this week, when your weather person says the wind chill is -20, it’s a dubious figure at best. That doesn’t mean you shouldn’t cover your skin when you go outside, especially if it’s windy.

But wind chill is nothing more than meteorological boasting, and as with most boasting, that means 1) there’s some exaggeration going on, and 2) nobody is that impressed, anyway.

Peter St. Onge

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