Wind Chill: Love It or Hate It, The Term is Here to Stay

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Home / Wind Chill: Love It or Hate It, The Term is Here to Stay

Chart used since 2001 for determining wind chill values. Image by NOAA

Meteorologists dislike ‘wind chill’: it’s inaccurate and was never intended for widespread use. One might wonder, considering the concept’s wide usage, if there’s a wind chill thermometer somewhere, or is it just a mathematical formula?

Consider this weekend. Ironically, with the polar vortex channeling skin-biting temperatures over much of North America, the number one movie was Disney’s ‘Frozen’; and it’s the the same weekend in which San Francisco defeated Green Bay in kickoff conditions of 5 degrees F, with northwesterly winds of 9 mph, producing a wind chill of minus-9. Did the spectators feel chilled?

Good question, right? If you visited the game from Florida, it might have been insufferable while the locals considered it just another winter’s day in Green Bay; there have been worse. In point of fact, how cold the wind makes you feel depends on all sorts of variables like your geographic origins, body type, and whether you’re sitting, or walking into the wind.

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What is Wind Chill?

First off, wind chill is a calculation, not a temperature measurement: Wind doesn’t change the air’s temperature. It simply blows away the thin layer of warm air that surrounds the skin. And the chilling effect of the wind varies with sunshine, each layer of clothing, wind breaks from buildings and trees, shifting wind gusts, and so on.

That said, wind chill, simply put, is the temperature of windless air that would have the same effect on exposed human skin as a given combination of wind speed and air temperature. The concept is important because cold and dangerous wind chills can lead to frostbites, hypothermia and even heart attacks.

History of Wind Chill Factor

The wind chill factor was first conceived in the Antarctic during the 1940s. Two polar scientists, Paul Siple and Charles Passel, wanting to know just how cold the air apparently was with the windy environment added in, conducted experiments on the time needed to freeze water in a plastic cylinder that was exposed to the elements. They found that the time depended on the warmth of the water, the outside temperature and the wind speed. The results were not reported as a temperature but rather as heat loss in watts per square meter.

A sample wind chill calculator: Choose a temperature, line it up with an arrow to obtain how cold it feels at selective wind speeds.  Image by Trevinci

A sample wind chill calculator: Choose a temperature, line it up with an arrow to obtain how cold it feels at selective wind speeds. Image by Trevinci

Then, in the 1960s, the weather services began to report wind chill as a wind chill equivalent temperature (WCET). This was theoretically less useful but was invented by weather services because listeners would not accept more scientific methods to help appreciate the difference between cold and windy.

As NOAA explains, “at first (WCET) was defined as the temperature at which the wind chill index would be the same in the complete absence of wind. This led to equivalent temperatures that were obviously exaggerations of the severity of the weather. Charles Eagan realized that people are rarely still and that even when it was calm, there was some air movement. He redefined the absence of wind to be an air speed of 1.8 meters per second (4.0 mph), which was about as low a wind speed as a cup anemometer could measure. This led to more realistic (warmer-sounding) values of equivalent temperature.”

For those who want to calculate wind chill, this was the formula they devised: Old Wind Chill T(wc)=.081 x (3.71 x sqrt(V) + 5.81 – 0.25 x V) x (T – 91.4) + 91.4 ; where T(wc) is the Wind Chill in degrees F, V is the Wind Speed in MPH, and T is the temperature in degrees F.

In the fall of 2001, the U.S. National Weather Service and the Canadian weather replaced the formulas with new ones (one for Fahrenheit temperatures and one for Celsius readings). The new formulas are based on greater scientific knowledge and on experiments that tested how fast the faces of volunteers cooled in a wind tunnel with various combinations of wind and temperature. The formula was changed to: New Wind Chill T(wc) = 35.74 + 0.6215T – 35.75(V0.16) + 0.4275T(V0.16)

The Geography of Wind Chill Factor

This author’s home is Canada. We love our wind chill. With such a big country it’s hard to unite Canadians on any subject but according to Dave Phillips of Environment Canada, reporting in the Globe and Mail, 82 percent say they will use wind chill.

But, in the 1980s, an experiment was run on the Prairies and in our North to move away from the ” -25 C feels like -37 C ” method into actually measuring  how much heat was lost each second over a given surface. In Winnipeg it produced this weather report: -28 C with a wind chill of 3,000 watts per square meter.

Atlantic Canada revolted from this scientific bent in weather reporting, and turned to indicating how many minutes it would take for skin to freeze. It is now passed on by Environment Canada and sometimes reported by weather services to its clients.

In Ontario and Quebec people held on to the more rudimentary calculation saying, for instance, the temperature is -34 C, but feels like -60 C.

Windchill vs. Feels Like: What’s the Point?

Just remember this: Wind chill factors may not make scientific sense, but this does. A jogger running open-faced into the wind will deal with far greater wind chill than a commuter completely bundled up waiting for a bus in a shelter. Both, however, will freeze to death if the actual temperature is cold enough, and they stay outside long enough.

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