What is wind chill? Understanding the wind chill index and how it's calculated

As temperatures plummet and the winds howl this winter, you'll hear about the dangers of the "wind chill." So what is it?

The wind chill temperature is how cold people (and animals) feel while outside. Wind chill is based on the rate of heat loss from exposed skin caused by the combination of wind and cold, according to the National Weather Service.

As the wind increases, it draws heat from the body, driving down skin temperature and eventually the body's internal temperature.

“It’s how it feels when you’re out in cold weather with wind blowing,” Bob Oravec, a lead forecaster for the Weather Service at the Weather Prediction Center, told Popular Science.

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What do wind chill numbers mean?

Therefore, the wind makes it feel much colder than it really is, so it's been described as a "feels-like" number. If the temperature is 0 degrees and the wind is blowing at 15 mph, the wind chill is 19 degrees below zero.

Low wind chill numbers shouldn't keep you from going out; they should encourage you to dress properly, however. For example, when the wind chill is around 40 degrees below zero, exposed skin can freeze in as little as 10 minutes.

How long can you be in wind chill?

Remember that the wind chill temperature is not some different kind of temperature: Wind chill alone can never make an object colder than the air temperature. Even if the wind chill is 10 degrees, you won't get frostbite or freeze your car's radiator if the air temperature is 32 degrees or above.

The Weather Service began to include wind chill in their forecasts in the early 1970s, several decades after Antarctic explorers first published research about it in the late 1930s.

The U.S. and Canadian weather services revised the wind chill index in 2001, 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.

How is wind chill created?

Here is a chart from the Weather Service for figuring out the wind chill, which is based on a formula that combines the current temperature with the current wind speed:

This article originally appeared on USA TODAY: Wind chill, explained: Here's how wind chill works and what it means.