Much of the country continued to grapple Tuesday with a historic freeze that shuttered schools and businesses at the start of the first full work week of 2014. Flights, trains and bus transportation were disrupted, thousands were left without power and even parts of the country used to fending off hypothermia and frostbite had to take extra precautions as temperatures and wind chills approached record levels.
Here are 10 things to know about the deep freeze.
1. WHAT IS A “POLAR VORTEX?”
A ‘‘polar vortex’’ is a counterclockwise-rotating pool of cold, dense air.
‘‘It’s just a large area of very cold air that comes down, forms over the North Pole or polar regions ... usually stays in Canada, but this time it’s going to come all the way into the eastern United States,’’ said National Weather Service meteorologist Phillip Schumacher in Sioux Falls, S.D.
2. THE COLD IS WIDESPREAD
Nearly 187 million people, more than half of the nation’s population, were under a wind chill warning or advisory.
The winds made it feel like 55 below zero at one point Monday in International Falls, Minn., and parts of the Midwest accustomed to temperatures that are cold — albeit seldom this cold.
But even the coal fields of Virginia and West Virginia had a wind chill of negative 35.
Every major weather-reporting station in Minnesota, North Dakota and Wisconsin noted temperatures below zero at 11 a.m. Monday, and South Dakota would have joined them if not for the 1-degree reading at Rapid City.
The coldest temperature reported in a 24-hour period through Monday was -36 degrees at Crane Lake, Minn. The warmest: 84 in Hollywood and Punta Gorda, Fla.
3. THOUSANDS OF FLIGHTS CANCELED
More than 3,700 flights — around one out of every 10 domestic departures — were canceled by Monday afternoon, following a weekend of travel disruption across the country. The bulk of those cancellations were in Chicago, Cleveland, New York and Boston.
‘‘It’s been one weather system after another,’’ said Delta Air Lines spokesman Morgan Durrant. ‘‘It’s been a challenging 72 hours.’’
With wind chills as low as 45 below zero at some airports, workers could remain exposed on the ramp for only a few minutes. That made loading and unloading luggage a challenge.
JetBlue Airways stopped all scheduled flights to and from New York and Boston. American Airlines said temperatures are so cold at Chicago’s O’Hare International Airport that fuel and de-icing liquids were actually frozen. United Airlines said its fuel is pumping slower than normal in Chicago.
Passengers reported long lines at airports as they tried to rebook on other flights. United Airlines had so many phone calls that it was suggesting travelers use its website to rebook.
In recent years, airlines have cut the number of flights to ensure that most of their planes depart full. That’s been great for their bottom line but leaves very few empty seats to rebook stranded travelers. Sometimes, it takes days to get everybody where they should be.
4. GROUND TRAVEL DISRUPTED, TOO
Planes weren’t the only form of mass transportation disrupted. There also were widespread delays and cancellations in ground transportation — including Amtrak, buses and commuter trains.
Officials with Chicago’s commuter rail, Metra, said there were multiple accidents, including one in which 14 passengers reported injuries — and six were taken to the hospital with minor injuries — after a train hit a ‘‘bumping post’’ at a downtown station.
Weather-related engine problems forced an Amtrak train carrying 200 passengers to stop for more than 8 ½ hours in southwestern Michigan before arriving early Monday morning in Chicago.
Drivers didn’t fare much better. A state emergency official said nearly 400 vehicles — including six semis — were stuck for several hours overnight Sunday along a snowy stretch of interstate in southern Illinois. Among them: The Southern Illinois University men’s basketball team, which spent the night on a church floor in central Illinois after their bus got stuck in a snowdrift on Interstate 57.
5. STORM LEAVES THOUSANDS IN THE DARK
Widespread power outages were being blamed on the storm, including in Indiana, where crews worked late Monday to restore services for more than 30,000 customers. Utility officials cautioned some people could be in the cold and dark until Thursday.
‘‘Due to the extreme conditions, damage is significant,’’ Indianapolis Power & Light spokeswoman Katie Bunton said.
State officials said places without power included the residential portion of the governor’s residence in Indianapolis.
Gov. Mike Pence noted during a news conference Monday that the house has ‘‘lots of fireplaces’’ but urged others without power to go to a shelter if necessary.
The city of Indianapolis evacuated more than 400 residents without heat or power, said Marc Lotter, a spokesman for Mayor Greg Ballard. Many found temporary comfort at warming centers set up around the city, while those needing long-term shelter were sent to the American Red Cross.
6. HEIGHTENED FEARS OF FROSTBITE, HYPOTHERMIA
In Chicago, hospital emergency rooms treated patients with frostbite, weather-related asthma and head injuries from falls on ice.
‘‘It’s pretty typical of what we see when it’s this cold,’’ said Dr. Paul Casey, an ER doctor at Rush University Medical Center. ‘‘Later in the day, the more people are outside working, we may see more cold-related injuries such as frostbite and hypothermia.’’
Cook County’s health system encouraged patients to reschedule their non-emergency appointments. Cook County’s Stroger Hospitals treated one homeless man with frostbite, said health system spokeswoman Marisa Kollias.
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.’’
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.
7. INCREASED RISK OF DEAD CAR BATTERIES
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 cannot 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.’’
8. POTENTIAL HARM TO CATTLE AND CITRUS
When temperatures plummet and the wind howls, ranchers have to protect themselves and their cattle in South Dakota.
Bob Fortune, of Belvidere, S.D., spent part of the weekend hauling hay and other feed to his cattle to prepare them for a wind chill expected to reach 50 or 60 degrees below zero. The cattle should be fine as long as they have feed and a place to get out of the wind, he said.
But with two freezing nights ahead in Louisiana, citrus farmers could lose any fruit they cannot pick in time. In Plaquemines Parish, south of New Orleans, Ben Becnel Jr. estimated that Ben & Ben Becnel Inc. had about 5,000 bushels of fruit on the trees, mostly navel oranges and the sweet, thin-skinned mandarin oranges called satsumas.
Becnel said he and his 10 workers should be able to get 1,000 bushels into boxes over the next two days.
‘‘If it doesn’t get below 25 for too long, some of the varieties will be OK,’’ he said. ‘‘Lemons freeze quick. The more sugar in the fruit, the longer it takes to freeze.’’
9. BEWARE SPACE HEATERS
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 US 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.’’
10. STAY BUNDLED DURING OUTDOOR EXERCISE
Stephen Regenold is a self-described fitness freak who has, he says, enjoyed winter his whole life. Now 36, Regenold runs five 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 live and not letting the weather man and the media scare me from what I love to do,’’ Regenold said.