Hazardous conditions in many states led to canceled flights and prompted warnings from transportation officials about venturing out onto the roads: Only those who absolutely need to should leave their homes.
Officials in Chicago and elsewhere canceled classes for Monday. In several states, government offices and courts have decided to shut down.
Local governments and charities worked to make sure shelters were available for anyone who needed them.
Even the South will be affected by the "polar vortex" of cold air, with temperatures there to fall well below normal Monday and Tuesday.
Temperatures are expected to dip into the 30s in parts of Florida on Tuesday, but the state's citrus industry isn't expecting any damage to crops. A spokesman for Florida Citrus Mutual said it must be at 28 degrees or lower for four hours straight for fruit to freeze badly.
Chicago Public School officials on Sunday reversed course, canceling classes for Monday ahead of the expected bitterly cold temperatures. The change in plans comes amid criticism from the Chicago Teachers Union, though officials said they made the decision after they "evaluated the situation again." Temperatures were expected to dip to minus 15 degrees on Monday, with wind chills of 40 to 50 below zero possible. The city was also walloped by snow on Sunday.
Numerous school districts, colleges, cities and counties announced they would be closed Monday as the National Weather Service warned of deadly wind chills as low as 45 below zero possible through Tuesday. The General Assembly also postponed the opening day of its 2014 session Monday. Gov. Mike Pence announced that all state government offices would be closed. And Indianapolis Mayor Greg Ballard upgraded the city's travel emergency level to "red," making it illegal for anyone to drive except for emergency personnel, emergency purposes or seeking shelter.
Even though the initial forecast for snow has been scaled back, flights for Monday and Tuesday were canceled at Barkley Regional Airport in Paducah. Organizations including churches and the Salvation Army were planning to open warming centers in some cities.
With two frigid nights on the way, New Orleans' city government said its freeze plan is in effect. All shelters will be open free of charge to people who need to get out of the cold. The city also encouraged residents to check on neighbors and the elderly.
The harshest winter conditions in 20 years are heading for Michigan, including temperatures expected to dive as low as minus 15. The Detroit Public Schools, Oakland University and hundreds of other schools from the southeastern Lower Peninsula to the western Upper Peninsula canceled Monday's classes.
A deep freeze that arrived in Minnesota on Sunday is to bring even colder temperatures Monday. Gov. Mark Dayton has ordered all public schools statewide closed Monday, a step no governor had taken since Arne Carlson called off classes Jan. 16, 1997. Wind chill warnings cover the state through Tuesday.
Missouri officials are warning residents to only go outside if they absolutely have to do so. The cold has made it difficult for the Missouri Department of Transportation to clear major roadways. The salt used to melt ice and snow hasn't been very effective because of the temperatures.
The forecast for Nebraska includes wind chills of 30 to 40 degrees below zero. That will be cold enough for frostbite to develop in about 10 minutes, so forecasters have extended a wind chill warning for the area into Tuesday.
Weather-weary New Jersey residents got a short-lived respite Sunday, as warmer temperatures started to melt the snow and ice spawned by last week's major storm. But forecasters say frigid temperatures will return Monday night, when lows will drop to the single digits and wind chills could reach 15 degrees below zero.
Winter weather caused the cancellation and delay of flights both to and from Nashville and Memphis on Sunday. The Metro Nashville government said it was partnering with local organizations to make sure shelters were available. Some school districts have canceled classes Monday due to the forecast.
The National Weather Service has issued wind chill warnings that take effect Monday evening from the Alleghany Highlands southeast to the Virginia Piedmont, including the Roanoke and New River valleys, and areas west of the Blue Ridge. Those areas could see wind chills of minus 30 degrees.
Dangerous cold air was forecast to become life-threatening Sunday night through Tuesday in Wisconsin. Strong winds will mean wind chills plummeting between 35 below to 60 below across the state. Gov. Scott Walker decided not to order schools to cancel classes statewide Monday, but he encouraged local school districts to make their own decisions. Many districts, including Milwaukee, Madison and Green Bay, told their students to stay home Monday.