The painfully cold weather system that put much of the US Midwest into a historic deep freeze is expected to ease, though temperatures could still tumble to record lows in some places before the region begins to thaw out.
Disruptions caused by the cold will persist, too, including power outages and cancelled flights and trains.
Before the worst of the cold begins to lift, the National Weather Service said Chicago could hit lows early on Thursday that break the city's record of minus 32C set on January 20, 1985. Some nearby isolated areas could see temperatures as low as minus 40C.
As temperatures bounce back into the single digits on Thursday, more people were expected to return to work in the nation's third-largest city, which resembled a ghost town after most offices told employees to stay home.
The blast of polar air that enveloped much of the Midwest on Wednesday closed schools and businesses and strained infrastructure with some of the lowest temperatures in a generation. The deep freeze snapped rail lines, cancelled hundreds of flights and strained utilities.
At least a dozen deaths related to extreme cold weather have been reported since Saturday in Michigan, Iowa, Indiana, Illinois, Wisconsin and Minnesota, according to officials and media reports.
Chicago dropped to a low of around minus 30C. Wind chills reportedly made it feel like minus 45C or worse.
The bitter cold was the result of a split in the polar vortex, a mass of cold air that normally stays bottled up in the Arctic. The split allowed the air to spill much farther south than usual.
Officials in dozens of cities focused on protecting vulnerable people from the cold, including the homeless, seniors and those living in substandard housing.
Aside from the safety risks and the physical discomfort, the system's icy grip also took a heavy toll on infrastructure, halting transportation, knocking out electricity and interrupting water service.
