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Heavy snowfall grounded flights and shuttered schools Monday in the Midwest, with worse on the way — Tuesday and Wednesday could be among Chicago's coldest days ever, with low temperatures forecast to be minus-18 and minus-21, respectively.

Chicago schools will be closed Wednesday, the school system said, while a decision on Tuesday's classes was still being considered Monday night. More than 1,400 flights were canceled Monday into and out of Chicago's O'Hare and Midway airports. More than 400 arrivals and departures on Tuesday were pre-emptively canceled.

It takes more than an extra pair of mittens and a hat to stay safe in those conditions.

"Having any skin exposed is not acceptable," said Tim Morris Jr., the fire prevention coordinator in Rockford, Illinois.

"Your forehead, the tip of your nose, your chin, your neckline — we want to cover all of those areas that we don't normally cover, and the next few days is the time to do that,” Morris told NBC affiliate WREX.

In North Dakota, heavy snow and freezing rain prompted the state Transportation Department to issue travel advisories in at least a dozen cities, while schools and government buildings in Wisconsin and Minnesota were closed as parts of those states braced for almost a foot of snow. Wisconsin Gov. Tony Evers declared a state of emergency.

Both Rockford and Chicago are likely to set multiple cold temperature records this week, including potentially the all time low for Rockford and the coldest daytime highs for both locations. Brutally cold wind chills also are expected Tuesday evening through Thursday morning. pic.twitter.com/bIZZ4kli7F — NWS Chicago (@NWSChicago) January 28, 2019

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Wind chill alerts extended across 14 states, from the northern Plains to the Ohio Valley.

At Town & Country Credit Union in Minot, North Dakota, the weather sign outside said it was minus-196 degrees on Monday. The credit union told NBC affiliate KFYR that a sensor was damaged.

The fact is that the wind chill was only minus-60.

Repeat: Minus-60.

Des Moines, Iowa, meanwhile, was forecast to shiver through wind chills of minus 50-degrees on Tuesday, according to the National Weather Service.

"The minus-40, -50, -60, you don't see that very often, and obviously you don't want to be outside any longer than you have to,” Frank Marcovis, co-owner of G&L Clothing in Des Moines, told NBC affiliate WHO.

A record cold air mass will continue into the central and northern U.S., spreading to the east coast on Tuesday. Wind chills of -30 to -60 can be expected over portions of the northern Plains and Great Lakes region. Please be safe. — NWS (@NWS) January 29, 2019

Marcovis said many customers were asking for the warmest pair of pants and bib overall he had in stock. But at temperatures like that, "that's kind of a relative term," he said.

TJ Knatcal, owner of TJK Plumbing in Minneapolis, said he answered 29 calls just for frozen pipes on Monday.

"It's going to be a busy week for us, that's for sure," he told NBC affiliate KARE.

Forecasters said that by midweek, Minneapolis and Green Bay, Wisconsin, will have suffered through about 80 hours with temperatures below zero, while Chicago will have faced 60 hours of the frigid temperatures. Officials urged people to stay inside and work from home if possible — which not everyone can do.

In the beautiful Midwest, windchill temperatures are reaching minus 60 degrees, the coldest ever recorded. In coming days, expected to get even colder. People can’t last outside even for minutes. What the hell is going on with Global Waming? Please come back fast, we need you! — Donald J. Trump (@realDonaldTrump) January 29, 2019

"It changes everything, and it makes things a lot different," said Rodney VanDeCasteele, chief of the Grand Ledge Area, Michigan, Fire Department.

"When you're fighting fires in the snow, one, you have the snow to deal with — you're going to have the slippery ground that you have to deal with," VanDeCasteele told NBC affiliate WILX of Lansing. "You're going to have water that's going to freeze, and everything that you try to gain access to seems a lot harder."

The University of Iowa, Iowa State University and the University of Notre Dame in Indiana canceled classes through Thursday. The last time Notre Dame closed in response to weather was five years ago.

A not-quite-as-brutal cold front will move to the Northeast later in the week. The region can expect wind chills dipping to minus 20-degrees.