Do you ever walk outside, having just checked the weather, and the wind punches you in the face?
The exposed parts of your body may feel like they're freezing. This phenomenon is called wind chill.
That's right, the weather term isn't a myth. Wind chill is real, so here's some facts to help you understand what it means and how to protect yourself:
What is wind chill?
Wind chill is essentially how cold people and animals feel when they're outside, according to the National Weather Service .
Wind chill is based on how much heat is lost from exposed skin while it's windy and cold. The faster the wind, the more heat is drawn from the body, which lowers the skin temperature and, ultimately, the internal body temperature.
"The critical thing is how long you can expose your skin before freezing," said Tom Sater, CNN meteorologist. "When the winds are stronger, it can whip the heat away from your body quicker."
Wind chill only applies to people and animals, the NWS says. The only effect wind chill has on inanimate objects -- such as cars or water pipes -- is that it shortens the amount of time it takes for the object to cool.
Why is it dangerous?
Wind chill can lead to frostbite, hypothermia and, ultimately, death.
Frostbite is caused by freezing of the skin and underlying tissues. It's most common on the fingers, toes, nose, ears, cheeks and chin, according to the Mayo Clinic. Severe cases can kill body tissue.
Hypothermia occurs when your body loses heat faster than it can produce it, the Mayo Clinic says. Left untreated, it can lead to the failure of the heart and respiratory system and, eventually, death.
Do you ever walk outside, having just checked the weather, and the wind punches you in the face?
How is wind chill measured?
The NWS says wind chill is for temperatures at or below 50 degrees and wind speeds above 3 mph.
Wind chill "takes into account the wind and how cold it is," CNN meteorologist Taylor Ward says.
So, the colder it is and the stronger the wind, the lower the wind chill.
In 2001, the NWS launched a new wind chill temperature index that features a useful formula for calculating the dangers of winter winds and freezing temperatures.
What's the difference between wind chill and wind speed?
Wind speed is just how strong the wind is, Ward says.
"Temperature and wind speed are the two components that go into the formula to figure out the wind chill, which is how cold it actually feels," he said.
When are wind chill advisories or warnings issued?
Wind chill advisory and warning criteria are issued locally, the National Weather Service says.
For example, wind chill advisories in New York City start at -15 degrees and warnings at -25.
In Chicago, advisories start at -20 degrees and warnings at -30 degrees.
And in Atlanta, advisories start at 5 degrees and warnings at -10.
Ward says the criteria for a wind chill warning or advisory is a sliding scale and takes climatology into account.
"People in the upper Midwest are most accustomed to the cold so the wind chill has to be lower than a place like the South to prompt a warning," he said.
How can people fight against wind chill?
Layers, layers and more layers.
"Cover all exposed skin. Face masks help," Sater said.
There is a myth about hats flying around that people need to wear one because 80% of the body's heat escapes from the head. Sater says exposing the head to wind chill and cold temperatures is no different than exposing an arm or leg.
