What is wind chill?

Wind chill is the apparent temperature felt on exposed skin due to wind. The degree of this phenomenon depends on both air temperature and wind speed. (Wikipedia).

In 2000, the National Weather Service brought together a large group of experts to revise the old Wind Chill Chart that was found to offer inaccurate wind chill values that were often far lower than they should have been. (Accuracyproject)







Other than the weather outside, this new interest in the wind chill came from this recent Slate article via Geekpress.

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Its ignoble history began with a pair of Antarctic explorers named Paul Siple and Charles Passel. In 1945, the two men left plastic bottles of water outside in the wind and observed the rate at which they froze.

...statements like "it's 5 degrees outside, but it feels like 40 below." What exactly did these phrases mean? The meteorologists would figure the rate of heat loss in watts per square meter and then try to match it up to an equivalent rate produced in low-wind conditions. For example, the rate of heat loss in 5-degree weather and 30 mph wind matched up with the one for minus-40-degree weather and very little wind. So, 5 degrees "felt like" 40 below.

(as above) - The updated model patches over the worst flaws of the old wind chill system, but it's not anything close to perfect. Osczevski and Bluestein made a set of new assumptions to determine wind-chill-equivalent temperatures. Namely, they geared their calculations toward people who are 5 feet tall, somewhat portly, and walk at an even clip directly into the wind. They also left out crucial variables that have an important effect on how we experience the weather, like solar radiation. Direct sunlight can make us feel 10 to 15 degrees warmer, even on a frigid winter day. The wind chill equivalent temperature, though, assumes that we're taking a stroll in the dead of night.

It doesn't tell you how cold your skin will get; that's determined by air temperature alone. Wind chill just tells you the rate at which your skin will reach the air temperature. If it were 35 degrees outside with a wind chill of 25, you might think you're in danger of getting frostbite. But your skin can freeze only if the air temperature is below freezing. At a real temperature of 35 degrees, you'll never get frostbite no matter how long you stand outside. And despite a popular misconception, a below-32 wind chill can't freeze our pipes or car radiators by itself, either.