A major snowstorm that lashed parts of the Midwest on Monday will give way to record-smashing cold this week as a powerful polar vortex drives a deep freeze across the eastern half of the nation, forecasters said.

A snowstorm will wreak havoc across the Deep South on Tuesday.

The bitter cold will bring below-zero temperatures to a quarter of the continental USA. The National Weather Service in Des Moines, Iowa, warned that "this is the coldest air many of us will have ever experienced." The service said that if people go outside, they should "avoid taking deep breaths, and minimize talking."

Schools could be closed in Iowa as buses may struggle to start, the weather service said.

Late Monday, Michigan Gov. Gretchen Whitmer declared a state of emergency to "help address threats to public health and safety related to forecast sub-zero temperatures over the next few days."

In a statement, Whitmer said, “Keeping Michiganders safe during this stretch of dangerously cold temperatures is our priority. Such widespread, extreme conditions have not occurred in Michigan for many years and it is imperative that we are proactive with record-low temperatures being predicted by the National Weather Service."

Wednesday could be the coldest day ever recorded in Chicago – a forecast high of 14 below zero, the weather service said. There's a chance the Windy City will break its all-time coldest temperature record of 27 degrees below zero. Chicago's famous Brookfield Zoo will be closed Wednesday and Thursday for only the fourth time in its 85-year history.

"Some locations in the Midwest will be below zero continuously for 48-72 hours," according to AccuWeather meteorologist Mike Doll.

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Weather.us meteorologist Ryan Maue said a "blend of models" shows that 55 million people in 24 percent of the continental USA could be at zero degrees or lower Wednesday morning. In Chicago, wind chills as low as 55 below zero are likely midweek, the weather service said. Some areas in the northern Plains could see wind chills of 64 degrees below zero.

Monday, parts of the Upper Midwest were under siege from a major snowstorm coupled with wind gusts of up to 40 mph that created blizzard-like conditions. Schools, courthouses and businesses were closed because of the storm. More than 1,000 flights were canceled.

In parts of Wisconsin, snow fell at a rate of 1 to 2 inches per hour. A foot fell in Camp Douglas, Wisconsin, as of late Monday, the highest snow total. Wisconsin Gov. Tony Evers declared a state of emergency Monday because of the snow and cold.

Behind the storm comes the deep freeze. The polar vortex – a vast area of cold air high up in the atmosphere that normally spins over the North Pole – will move down from the Arctic Circle and park itself over the Great Lakes.

Low temperatures Tuesday night will dip to 30 below zero across much of North Dakota, South Dakota and Minnesota. Temperatures in Chicago could drop to 25 below zero for the first time since the mid-1980s, AccuWeather warned.

Highs on Wednesday may not exceed 10 below zero from Fargo, North Dakota, to Minneapolis and Chicago. Single-digit temperatures will have people shivering from Kansas City, Missouri, to St. Louis to Cincinnati and Pittsburgh, AccuWeather said.

All-time record wind chills of near 50 below are possible in northern Indiana. In northern Minnesota, the wind chill predicted for Wednesday morning "could cause frostbite to exposed skin in less than 5 minutes," the National Weather Service said.

The East Coast will get only a modest reprieve – lows Wednesday night will reach 6 degrees in New York, 7 degrees in Philadelphia and a "balmy" 9 degrees in Washington.

As cold and snow slam into the North, a snowstorm will paste the Deep South on Tuesday and Wednesday.

"A couple inches of snow can fall in Jackson, Mississippi; Birmingham, Alabama; and Chattanooga, Tennessee," AccuWeather meteorologist Kristina Pydynowski said. "Travel can become slippery and treacherous as roads rapidly turn from wet to slushy and icy."

AccuWeather meteorologist Rob Richards said, "Atlanta could even receive a coating to an inch of snow."

Sunday, a prelude to the polar plunge slammed into the Upper Midwest with temperatures reaching below zero in the morning. The low of 45-below zero in International Falls, Minnesota, smashed a record that stood for more than half a century.

The worst is yet to come, Doll said.

“I cannot stress how dangerously cold it will be,” he said. "An entire generation has gone by without experiencing this type of cold."

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Shelly Sarasin, co-founder of Street Angels Milwaukee Outreach, said her members have been hitting the streets, looking for people in need of warmth.

"We have been out every night until at least midnight, picking people up from their homeless camp or emergency room pickups," she said. "It's been lifesaving for many people."

Contributing: Meg Jones and James B. Nelson, Milwaukee Journal Sentinel; The Associated Press