By Holly Yan and Joe Sutton
(CNN) -- How low can it go?
The deep freeze gripping two-thirds of the United States has temperatures plummeting to unbelievable lows Monday.
Much of the country will see the coldest temperatures in almost 20 years, the National Weather Service said. Some cities will experience chills 30 to 50 degrees below average.
To put things in perspective, the weather in Atlanta and Nashville on Monday will be colder than in Anchorage, Alaska.
And by Wednesday, nearly half the nation will shudder in temperatures of zero or lower, forecasters said.
Here's what to expect across the country:
Astonishing cold in the Midwest
At this point, zero degrees sounds balmy.
The afternoon "high" temperatures in parts of the Midwest won't even get up to zero on Monday, the National Weather Service said.
Throw in some fierce winds, and you get wind chills like 55 below zero in Duluth, Minnesota; minus 34 in Chicago; and minus 24 in St. Louis.
The extreme weather prompted school cancellations Monday in many major school districts, including St. Louis, Chicago, Detroit, Indianapolis and Milwaukee.
"It's not just a snow event, it's a cold event, and that's what scares us," Indianapolis Mayor Greg Ballard said. He urged residents to stay off the streets, especially after nightfall.
The Southern Illinois University men's basketball team, fresh off a game against Illinois State, got trapped on the side of Interstate 57 late Sunday and was prepared to spend the night on the bus, SIU Athletic Director Mario Moccia said.
There wasn't a massive amount of snow on the ground, Moccia said. Rather, it was the blowing snow that made the road virtually impossible to see.
The bus driver decided to pull off the road and get out of the way of traffic until visibility improved. But when the driver tried to get back on the road, there was no traction, and the bus was stuck.
"They're just hanging out, they're watching movies," Moccia told CNN late Sunday night. He said the bus had plenty of fuel, heat and food, and the team was waiting for a tow truck.
Players later tweeted that they were going to spend the night at a nearby church in Tuscola, Illinois.
"Somehow this eventful day/night has led to our team sleeping on the floor of a church in Tuscola. What a journey it has been," Dawson Verhines tweeted.
In Embarrass, Minnesota, residents wondered whether they might see their cold-temperature record of 64 below zero, set in 1996, snap like an icicle.
"I've got a thermometer from the weather service that goes to 100 below," resident Roland Fowler told CNN affiliate KQDS. "If it gets that cold, I don't want to be here."
Deep freeze in the Deep South
This isn't a joke. Hard freeze warnings are in effect across much of the Deep South, from eastern Texas to Florida. That includes virtually all of Louisiana until late Monday morning, the National Weather Service said.
The arctic blast threatens to sweep subzero lows as far south as Alabama and plunge much of the Deep South into the single digits.
Tennessee declared a state of emergency as it braced for the coldest temperatures since 1994 on Monday.
"Temperatures will not get above freezing until Wednesday night," the Tennessee Emergency Management Agency said. It warned of rapidly falling temperatures and slick roads from flash freezing.
More than 2,400 flights have been canceled within, into or out of the United States for Monday, according to Flightaware.com, which tracks cancellations based on both weather and mechanical problems.
That's on top of the 3,800 flights canceled on Sunday.
John F. Kennedy International Airport in New York was closed briefly Sunday morning after a plane carrying 32 passengers skidded into a snowbank while turning onto a taxiway. No injuries were reported.
As if the brutal cold isn't bad enough, tens of thousands of Midwesterners are dealing with no electricity.
More than 15,000 customers in Indiana, 6,800 in Illinois and 2,200 in Missouri didn't have power overnight, according to utility companies.
Chicago opened up 12 centers for residents to seek warmth, one of which was to stay open all night through Tuesday. Libraries and some other city facilities would also be open, said Evelyn Diaz of the city's Department of Family and Support Services. Illinois Gov. Pat Quinn said 100 warming centers were open statewide.
The plunging temperatures and wind chills are a dangerous recipe for rapid frostbite or hypothermia.
"Exposed flesh can freeze in as little as five minutes with wind chills colder than 50 below," the National Weather Service's Twin Cities office in Minnesota said.
Over the past week, at least 13 people have died from weather-related conditions.
Eleven people died in road accidents -- including one man crushed as he was moving street salt with a forklift.
One man in Wisconsin died of hypothermia. And an elderly woman with Alzheimer's disease in New York state wandered away from her home and was found dead in the snow in a wooded area about 100 yards away.
This, too, shall pass
If there's any good news about the biting cold snap, it's that most of it should be over by Wednesday. That's when a warming trend should begin, the National Weather Service said.
In the meantime, those in the western part of the country don't have to worry at all. Most of the West can expect relatively pleasant weather through Tuesday.
CNN's Indra Petersons, Todd Borek, AnneClaire Stapleton and Julia Lull contributed to this report.
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