A chart shows how people across the US could get frostbite within minutes this weekend as winds force temperatures below minus 20 degrees Fahrenheit

• Millions of people could get frostbite within minutes over the holiday weekend, experts warned.
• Frostbite is when the skin freezes after exposure to cold temperatures, which can cause permanent damage.

Millions of people could get frostbite within minutes over the holiday weekend, meteorologists warned, as high winds rip across the US and drive temperatures below minus 20 degrees Fahrenheit in some areas.

More than 200 million Americans, which is about 60% of the US population, were under some form of winter weather alert —including "wind chill warnings" for 181 million — on Friday, the National Weather Service said. It called the "powerful Arctic" conditions from an "immense weather storm" that stretches coast-to-coast "historic."

"Wind chill" is based on the rate of heat loss from exposed skin caused by wind and cold. According to the NWS, the windier it is, the more heat is drawn from the body, which drives down skin temperature, putting people at risk of frostbite.

Frostbite is when the skin freezes after exposure to cold temperatures, which can cause permanent damage, according to the American Academy of Dermatologists. Sometimes, the tissue below the skin freezes too.

The criteria for official NWS wind chill warnings are set locally. For example, in Rochester, New York, warnings get issued when the wind chill temperature is minus 25 F or below.

The National Weather Service windchill chart shows how quickly you can get frostbite

The NWS has a chart that shows how long it takes to get frostbite at certain temperatures and wind speeds. For example, if it is 0 F and the wind is blowing at 15 mph, the wind chill is minus 19 F and exposed skin can freeze in 30 minutes.

The NWS told Insider in an email on Friday that over the next week the northern Rockies, northern and central Plains, Midwest, and Ohio Valley will experience wind chills below minus 20 F, when frostbite can occur within minutes, and wind chills below 30 F may reach Central Florida.

Red or painful skin can be a sign of frostbite

The Centers for Disease Control and Prevention states that early signs of frostbite — which usually affect the nose, ears, cheeks, chin, fingers, or toes — are redness or painful skin.

People that experience those symptoms should get out of the cold or protect exposed areas with clothing or blankets.

Other signs of frost bite include: a white or grayish-yellow area of skin, skin that feels unusually firm or waxy, and numbness.

People who have poor circulation or aren't wearing adequate clothing are more likely to get it, the CDC states.

"Wearing lots of layers of clothing and really limiting your time outside when we have these extremely cold wind chills is really important," Megan Jones, a meteorologist at the Bismarck National Weather Service, told KFYR-TV.