A blast of bone-chilling cold reaching lows not seen in two decades gripped the United States early Tuesday, snarling air travel, closing schools and prompting calls for people to stay inside.
Superlatives abounded, even in midwestern states used to chest-high snow and bitter cold, as the National Weather Service said the deep freeze was making its way east.
Air travel was a nightmare, stranding many travellers trying to head home from holidays.
More than 4300 US flights were cancelled on Monday - nearly half of those in Chicago - and more than 6500 were delayed, according to FlightAware, a flight-monitoring site.
Airline JetBlue said it was reducing operations at four airports in the bustling northeast corridor - JFK, La Guardia, Newark and Boston - until 10am Tuesday (01:00 AEDT Wednesday).
More than a dozen deaths were blamed on the frigid weather.
A shift in a weather pattern known as the "polar vortex" triggered a drastic drop in temperatures, coinciding with wind chill warnings in much of the east of the country.
Comertown, Montana, recorded the lowest wind chill value so far at minus 53C while North Dakota, South Dakota and Minnesota were not much warmer.
That was significantly colder than the South Pole, which recorded a wind chill reading of minus 33C.
In Minneapolis, Minnesota, where people scoff when cities like Washington DC panic and shut down with even a moderate snowfall, the newspaper The Star Tribune gave a graphic description of what happens when, for instance, the overnight temperature Monday hit minus 23C.
"The windchill and cold are freezing exposed flesh in five minutes," it said.
The paper said life has "slowed to a crawl across the state."
"It's a blistering cold spell destined for Minnesota winter weather lore," it added.
Even the typically temperate Deep South was feeling the chill with a hard freeze warning threatening crops and livestock.
Early Tuesday in Washington DC, the temperature was a relatively mild minus 11C early Tuesday, but blustery winds blew leaves and trash swirling in the air.
Deaths blamed on the frigid weather included a 71-year-old woman suffering from Alzheimer's disease, who froze to death after getting lost in New York state.
The body of a 90-year-old woman was found face down in the snow next to her car in Ohio on Monday morning, the Toledo Blade reported.
At least a dozen other people were reportedly killed in crashes on icy roads, including four people whose sport utility vehicle slid off a rural Minnesota highway and fell into the Mississippi River.
Four Chicago men aged 48 to 63 died of apparent heart attacks while shovelling the snow over the weekend, the Chicago Tribune reported.
Chicago was among scores of towns and cities which told parents to keep their children at home rather than risk sending them out, while the governor of Minnesota cancelled school across the entire state on Monday.
Illinois Governor Pat Quinn praised the "heroic" efforts of National Guard troops who cleared a 375-vehicle backup and a forestry officer who rescued seven stranded people and two of their pets using a snowmobile.
Indianapolis mayor Greg Ballard barred everyone except emergency workers from driving at the height of the storm Sunday and urged residents to stay indoors unless absolutely necessary on Monday.
"This extreme cold poses a serious health and safety risk," he warned.
But with thousands of people without power after electrical lines were felled, home was not always the best option.
Those who couldn't stay with family or friends were urged to seek out community centres which were opened as temporary shelters.
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