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January 6, 2014

What does the wind chill factor really mean?

A brief history of the wind chill factor and why we use it.

With the bitterly cold air dominating our local news today, the phrase “wind chill factor” is getting a great deal of well-deserved attention. Some people are asking what it really means and when we started using it.

Before World War II, two scientists working in Antarctica first developed the idea and coined the phrase. Paul Allman Siple and Charles Passel based it on the cooling rate of a bottle of water that was suspended above their hut. They developed a formula and made a chart that was later released and became widely used in the 1970s. Then in 2001, the National Weather Service updated the formula used to calculate the wind chill. That updated version is what we use today.

The idea behind the wind chill factor is to give people an idea of just how quickly the cold temperatures mixed with the wind will affect humans and animals alike. Frostbite and hypothermia are real dangers from bitter cold, and the wind chill factor helps determine the level of danger we face.

The formula takes into account the temperature and winds at five feet above ground level, the average height of an adult’s face, which is presumably the most exposed part of the body on a cold day. According to the National Weather Service, it also “incorporates heat transfer theory, heat loss from the body to its surroundings, during cold and breezy/windy days.” The National Weather Service Windchill Chart states that at a wind chill of about -19º, frost bite can occur in thirty minutes. Of course, below that temperature, the colder it is, the faster frostbite will happen.

You might have heard all the hype surrounding the Green Bay vs. San Francisco game yesterday. Last week, some meteorologists were predicting the wind chill would be colder than the famed Ice Bowl of 1967. In fact, that forecast did not pan out, partially because in the 1960s, they were still using the older formula, which caused the calculations to be colder than they should have been. By the old index, the wind chill for the Ice Bowl was -47º. By the new index, it was a warmer -36. Also, the actual temperature in Green Bay yesterday was not nearly as cold as was feared by some late last week.

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