A deadly chill had much of the United States and Canada in its wintry grip yesterday as a record-breaking cold snap brought temperatures lower than on the surface of Mars.
It was so cold in Chicago that the polar bear at the Lincoln Park zoo - who admittedly had not built up the winter fat stores of her wild cousins - was brought inside to warm up.
In Kentucky, an escaped inmate begged to be let back into prison so he could warm up after spending the night shivering in an abandoned house.
All of Canada and all the American states bar tropical Hawaii recorded temperatures below freezing on Tuesday, even in usually sunny and warm Florida and California.
But the most dangerous cold - temperatures that can cause frostbite in a minute and death in a matter of hours - hit the Midwest as the "polar vortex" brought frigid air from the Arctic.
Schools, businesses and government offices were closed. Water mains and household pipes froze. Airplanes were grounded, trains were halted and roads and pavements became ice rinks.
The town of Embarrass, Minnesota, recorded the lowest temperature in the US at minus 37 degrees Celsius. The wind chill, representing how much colder it feels when the blinding gusts hit you in the face, dipped as low as minus 52 degrees in Montana. That's cold enough to toss a cup of boiling water into the air and watch it turn into snow before it hits the ground.
Video: Huge swath of the United States in the grip of Arctic blast
The Mars Rover has been sending back daily temperature readings ranging from minus 25 to minus 31 degrees.
For a more earthly comparison, the Amundsen-Scott South Pole Station recorded a temperature of minus 23 degrees and a wind chill factor of minus 35 degrees on Tuesday.
The brutal chill came as people in the Great Lakes region were still digging out from two massive snow storms.
More than 500 people spent Monday night stuck on a train that was stranded by snowdrifts on the line between Detroit and Chicago. Commuter railways, and even Chicago's famed elevated trains, were knocked out of service by temperatures that froze switches and signals.
Nearly 2,500 flights were cancelled in the US on Tuesday and 3,400 were delayed. That brought the total of flights cancelled since the latest snowstorm hit on Thursday to more than 18,000.
Toronto's Pearson International Airport temporarily halted ground operations early on Tuesday because of "equipment freezing" and out of concern for the safety of airport personnel.
Police reinforcements were called in to the airport to deal with rising tension among stranded travellers.
The governor of Illinois declared a state of emergency on Monday and called up the National Guard to help rescue stranded motorists as high winds whipped up blinding snow.