There's cold. And then there's subzero, frostbite cold.
Record-breaking frigid temperatures will blanket the Midwest beginning Sunday, part of a "polar vortex," that one meteorologist says will send piles of North Pole air down into the U.S.
These below-zero temperatures can be dangerous, and officials in several states are warning residents to take precautions. Here's a look at some of the problems that arise when temperatures plummet and how to stay safe if you venture outdoors.
At temperatures of 15 to 30 below, exposed skin can get frostbitten in minutes and hypothermia can quickly set in.
"People need to protect themselves against the intense cold," said Dr. Brian Mahoney, medical director of emergency services at Hennepin County Medical Center in Minneapolis. "They have to wear a hat, they have to have face protection."
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Mahoney said mittens are better than gloves, layers of dry clothing are best, and anyone who gets wet needs to get inside.
"You can't be wearing high-heel shoes with your toes in nylons," he added. "That's a great way to get frostbite."
Hypothermia, when a person's total body temperature gets too low, could lead to unconsciousness or cardiac arrest. Frostbite, when extremities freeze, could lead to amputations.
Homeless people who have no relief from the bitter chill are at risk, but Mahoney said he's also treated people who simply used bad judgment, sometimes due to drinking alcohol.
The bottom line, Mahoney said, is to avoid the cold if you can -- or make sure all body parts are covered up and covered up well.
You could die if you don't respect the environment you live in," he said.
Keeping vehicles in a garage is the most surefire way to ensure they will start in subzero conditions.
But for those who don't have access to a garage, it's important that they check the health of their vehicle's battery before the cold arrives, said Jason Jones, who works for Best Batteries in North Kansas City, Mo. -- where temperatures early Monday were forecast to reach 10 degrees below zero.
Most batteries less than three years old should be able to handle the cold, he said. Older batteries and ones that are on the verge of going dead often can't even be jump-started once they have been exposed for an extended time to temperatures below zero.
"Some batteries you can't get back to life," Jones said. "Once they get to a certain point, they're done."
Brandie Nixon awoke the Saturday before Christmas to the screams of her 6-year-old son, Kurtus, and then saw smoke and fire in the bedroom of the family's small home in St. Clair, Mo.
A portable heater had somehow ignited a toy box, the fire eventually spreading to the bed where Kurtus was sleeping. Fortunately, he awoke in time to scamper to safety.
"The house didn't have heat," Nixon, a 25-year-old Wal-Mart employee, said, explaining the use of the portable heater. "I would not use heaters again. It's too risky."
The U.S. Fire Administration says more than 50,000 residential fires annually are caused by heating, resulting in about 150 deaths. January is the peak month.
"I think it's principally a desperation thing," said William Siedhoff, director of Human Services for the city of St. Louis. "When you're freezing cold, sometimes logic goes out the window and you seek out whatever means you can to stay warm."
Stephen Regenold is a self-described fitness freak who has, he says, enjoyed winter his whole life. Now 36, Regenold runs 5 miles daily around Minneapolis' Lake Calhoun, and bikes to work every day no matter the weather.
"I go crazy if I don't get those endorphins and get those fitness fixes every day," Regenold said.
Regenold's other love is equipment, which he writes about as the "Gear Junkie." Looking for pro tips for outdoor athletic survival? He's got them.
Keeping the core warm is easy, he says; focus instead on extremities. He wears mittens, and on the coldest days swears by a versatile hat that can be worn to cover neck, head or both (He often wears two, plus a regular winter hat).
"To me it's less about being tough, but more about embracing where I love and not letting the weather man and the media scare me from what I love to do," Regenold said.
Extreme temperatures also can cause plenty of other problems that can strand drivers -- even those who drive school buses.
In St. Louis County, one school district canceled classes Friday after 20 of its buses wouldn't start, and 85 others didn't have working air brakes because of temperatures that hovered around zero at 6 a.m.
Crews will be working over the weekend to make sure the company's buses are in good mechanical condition, said Stephanie Creech, a spokeswoman for Cincinnati-based First Student Inc., which operates buses in the Rockwood School District. But there's no guarantee that they will be able to operate when the mercury drops below zero.
"Monday, it would appear there could be safety issues," Creech said. "Delays could be severe enough that students might not be picked up in a timely manner, and if so we will make a recommendation to the school systems that we don't operate the buses."