MINNEAPOLIS (AP) -- It's not the heat, it's the humidity, goes the old saying. For the tens of millions of Americans currently trapped in the deep freeze: It's not the cold, it's the wind.
Air temperatures plunging into the negative teens, twenties and even thirties Sunday into Monday are bad enough. But add wind speeds of even a few miles per hour, and what's already deeply unpleasant becomes downright dangerous.
"It's not so much the absolute cold, though that's certainly not pleasant either," said Mark Seeley, a climatologist for the University of Minnesota. "But what the wind does when it starts blowing it around is force the cold air onto whatever it touches. Whether it's human skin or a car engine, the wind pushes away the warmth being generated and replaces it with cold."
Thus the popular term "wind chill," which a couple of Polar explorers originated in 1945 to differentiate between the actual temperature, and the temperature that it feels like thanks to the wind. For instance: In International Falls, Minn., along the Canadian border, it was forecast to reach an air temperature of 30 below zero early Monday. But wind gusts will make it feel more like negative 60.
"Fighting a fire on a night like that, a lot of our guys would rather do recon in the burning structure than man the hoses," said Jim Hultman, a veteran firefighter in International Falls, frequently one of the coldest spots in the nation. "I'm not kidding. Because at least you're warm."
Hultman said cold winds ice up the nozzles, slow the water streams and blow an icy mist onto the firefighters. "It's just miserable," said Hultman, 59, adding in an interview Sunday that he's "nine shifts away from retirement and then I'm headed someplace warm for a few months."
Severely low wind chills are a serious threat to the human body. "Really, the best advice I can give is don't go outside at all unless you absolutely have to," said Douglas Brunette, an emergency room doctor at Hennepin County Medical Center in Minneapolis. Skin exposed to such wind chills can develop frostbite within five minutes; hypothermia comes close behind.
"I have seen frostbite occur through clothing," Brunette said. "It's not enough just to be covered. You need clothes made for the elements. You need to repel the wind."
Right now, winds are blowing arctic air across large swaths of the United States. Temperatures were being suppressed by what meteorologists called a "polar vortex," a rotating pool of frigid air forecast to affect more than half the continental U.S. into Tuesday. Wind chill warnings were stretching from Montana to Alabama.
"I've lived in Minnesota or Wisconsin most of my life. You figure out how to be prepared," said Jesse Roehl, a 39-year-old marketing manager who ventured out Sunday to a Minneapolis grocery store for provisions. Swaddled in a parka, heavy boots, stocking cap, scarf, gloves and several layers underneath, Roehl said he was amused by the fashion choices forced by the wind chill factor.
"Function over fashion," he said. "Even teenagers are wearing stocking caps today."
In Columbus, Ohio, 43-year-old student and consultant Lorna West was worried for Ohioans and residents of other states not used to such frosty blasts.
West, a Chicago native, said she couldn't explain the exact science of wind chills, "but I understand the basic, which is it's going to be damn cold."
Few know the brutality of the winter wind more than lifelong Minnesotan Will Steger, an explorer who has traveled by dogsled to both poles. Steger said even with the coldest temperatures, a few miles per hour of wind make a huge difference.
"A minus 50 day with no wind is a pleasant day if your body is working, it's not that bad," Steger said. "But a minus 30 day with a 10 mile per hour wind is much, much colder. The wind drives the cold in, it magnifies it. It pushes it into your skin."
Steger said the only thing he liked about the wind on polar expeditions was the sound it made at night.
"It's a melody. It lulls me to sleep," he said. "What I didn't like was waking up in the morning and hearing it, because you know you have to go back out and face it again."
Associated Press reporter Julie Carr Smyth in Columbus, Ohio, contributed to this report.