A Moment of Science

How Cold Does It Feel?

Now, a brief history of the wind chill temperature index. If you’re enough to live where it’s sometimes windy and cold, you’ve probably heard your weatherperson give out two temperatures, the actual temperature outside, and a temperature based on the wind-chill temperature index. The first tells you how cold it actually is, and the second tells you how cold it feels given current wind conditions.

While the fact that a gust of wind can really cool things down might seem like a no-brainer, actually calculating the wind-chill temperature index is quite complex. Back in 1945 the scientists who came up with the original index did so based on how long it took plastic cylinders full of water to freeze under different conditions.

The catch, of course, is that humans and animals don’t have much in common with plastic cylinders. That’s why in 2001 the National Weather Service adopted an updated wind-chill temperature index which accounts for the way our bodies lose heat to their surroundings. This new formula is also based on several assumptions. For one thing, it assumes that people wrap up in cold weather, so they lose most of their heat through their face. And because the average face is about five feet high, the wind speed measurement is calculated there rather than at the national standard height of 33 feet like it was before.

Of course, even this new formula isn’t perfect. It doesn’t take into account whether it’s sunny or snowing, and contact with moisture makes quite a difference in terms of heat loss. Still, it’s far more accurate, which sure comes in handy when you’re trying to avoid that frostbite.

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