In Pics: Winter Has Come to US Midwest as Polar Vortex Hits

People get on course with their daily lives, because they would still freeze to death sitting at home.

A harbor light is covered with snow and ice on the Lake Michigan at 39th Street Harbor, Wednesday, 30 January 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures on Wednesday.

(Photo: AP Photo/Nam Y Huh)

Current low temperatures “could easily freeze the flesh off your bones.”

That is the warning that the US National Weather Service gave its citizens.

A person walks along the lakeshore, Wednesday, 30 January 2019, in Chicago. Widespread closures of schools and businesses has prompted the US Postal Service to take the rare step of suspending mail delivery to a wide swathe of the region.(Photo: AP Photo/Kiichiro Sato)

In Illinois, temperatures could rise by 80 degrees within days. In Michigan, melting snow and rain and a 17-mile ice jam could lead to flooding. Across the Midwest, the sudden warmth was sure to bring more broken roads and busted water mains.

Photographers set up tripods along the shore of Lake Michigan before sunrise, Thursday, 31 January 2019, in Chicago. The painfully cold weather system that put much of the Midwest into a historic deep freeze was expected to ease Thursday, though temperatures still tumbled to record lows in some places.(Photo: AP Photo/Kiichiro Sato)

The polar vortex that brought many cities to a standstill was expected to end with a rapid thaw that experts say could be unprecedented. But the sudden swing from long johns to light jackets and short sleeves could create problems of its own.

Ice forms along the shore of Lake Michigan before sunrise, Wednesday, 30 January 2019, Chicago.(Photo: AP Photo/Kiichiro Sato)

"I don't think there's ever been a case where we've seen (such a big) shift in temperatures," in the winter, said Jeff Masters, meteorology director of the Weather Underground firm. "Past record-cold waves have not dissipated this quickly and here we are going right into spring-like temperatures."

Geese huddle in the water as the sun rises at the harbour in Port Washington, Wisconsin, on Wednesday, 30 January 2019. A deadly deep freeze enveloped the Midwest with record-breaking temperatures.(Photo: AP Photo/Jeffrey Phelps) 

On Thursday, the system marched east, spreading arctic conditions over an area from Buffalo to Brooklyn. In western New York, a storm that dumped up to 20 inches of snow (51 centimetres) gave way to subzero temperatures and face-stinging wind chills

The sun rises behind icicles formed on the harbour in Port Washington, Wisconsin, on Wednesday, 30 January 2019, A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures. (Photo: AP Photo/Jeffrey Phelps) 

In New York City, about 200 firefighters battling a blaze in a commercial building took turns getting warm on buses. The number of deaths that could be blamed on the cold climbed to at least 15.

Morning commuters face a tough slog on Wacker Drive in Chicago, Monday, 28 January 2019.(Photo: Rich Hein/Chicago Sun-Times via AP)

For the nation's midwest, relief was as close as the weekend.

Rockford, Illinois, was at a record-breaking minus 31 (minus 35 Celsius) on Thursday morning but should be around 50 (10 Celsius) on Monday. Other previously frozen areas could see temperatures of 55 (13 Celsius) or higher.

Commuters wait for a train as snow falls Monday, 28 January 2019, in Chicago. Wind chills could dip to negative 55 degrees in northern Illinois, which the National Weather Service calls “possibly life threatening.”(Photo: AP Photo/Kiichiro Sato) 

The dramatic warm-up will offer a respite from the bone-chilling cold that canceled school, closed businesses and halted trains. But potholes will appear on roads and bridges weakened by the freeze-thaw cycle. The same cycle can crack water mains and homeowners' pipes. Scores of vehicles will be left with flat tires and bent rims.

Chicago’s El trains move along snow-covered tracks Monday, 28 January 2019, in Chicago. The plunging temperatures expected later this week that have forecasters especially concerned. (Photo: AP Photo/Kiichiro Sato) 

Joe Buck, who manages Schmit Towing in Minneapolis and spent about 20 hours a day outdoors this week responding to stranded vehicle calls, said he's already taking calls for Monday to deal with a backlog of hundreds of stalled vehicles.

A Metra train moves southbound to downtown Chicago as the gas-fired switch heater on the rails keeps the ice and snow off the switches near Metra Western Avenue station in Chicago, Tuesday, 29 January 2019. Forecasters warn that the freezing weather Tuesday will get worse and could be life-threatening.(Photo: AP Photo/Kiichiro Sato)

In Detroit, where some water mains are almost 150 years old, city workers were dealing with dozens of breaks, said Palencia Mobley, deputy director of the Detroit Water and Sewerage Department.

New York firefighters battle a blaze in a commercial building in the Bedford Stuyvesant neighbourhood of Brooklyn, Thursday, 31 January 2019 in New York. Firefighters around New York state have been grappling with brutal cold during big blazes.(Photo: AP Photo/Mark Lennihan)

"We'll have all hands on deck. Hopefully, we'll be able to address as many of the issues as possible over the next week," Mobley said.

The thawing of pipes can sometimes inflict greater damage than the initial freeze. Bursts can occur when ice inside starts to melt and water rushes through the pipe, or when water in the pipe is pushed to a closed faucet by expanding ice.

Frost covers part of the face of University of Minnesota student Daniel Dylla during a morning jog along Mississippi River Parkway Tuesday, 29 January 2019, in Minneapolis. Extreme cold and record-breaking temperatures are crawling into parts of the Midwest after a powerful snowstorm pounded the region.(Photo: David Joles/Star Tribune via AP)