N America weather: Polar vortex brings record temperatures
Forecasters say the Mid-West could see record low temperatures
Parts of the US are braced for potentially record-breaking low temperatures as a "polar vortex" brings more freezing weather.
A winter storm has already blanketed areas of Canada and the north-eastern US with up to 2ft (60 cm) of snow.
It has been blamed for 16 deaths and the cancellation of more than 5,000 flights since Wednesday.
A plane from Toronto has slid into snow as it turned onto a taxiway after landing at New York's JFK airport.
No-one was hurt in the incident but all flights at the airport were suspended for two hours because of icy runways.
The plunging temperatures result from the polar vortex, a counter-clockwise-rotating pool of cold, dense air.
US cold plunge continues
Forecasters say temperatures in the US Mid-West could feel as low as -58F (-50C) with the effect of wind chill.
Authorities have warned residents to remain indoors, both for their own safety and to keep roads clear for snow removal.
In Canada, tens of thousands of people on the island of Newfoundland remain without power due to a transformer fire linked to heavy snow.
'Bitterly cold'"The coldest weather in years will be making its presence known from the Upper Mid-West to the Mid-Atlantic region," the US National Weather Service said in a statement.
The states of Ohio, South Dakota and Illinois are among those set to be hit.
The weather service said "an incredibly strong surge of bitterly cold Arctic air" would sweep across the country from Saturday night until Tuesday.
It is set to continue to the north-east, where residents are still digging out from the week's deadly snowstorm.
Temperatures as low as -50C are forecast for the US Mid-West 
A winter storm warning is in place in Chicago 
Residents in New Jersey have been clearing up after this week's snow storm It could bring some of the coldest temperatures in two decades.
"The last really big Arctic outbreak was 1994," Reuters news agency quoted Bob Oravec, a forecaster with the National Weather Service, as saying.
"Outbreaks like this don't occur everyday."
In Canada, the temperature dropped as low as -29C (-20F) in Toronto and -38C in Quebec City with wind chill on Thursday - the lowest seen in at least two decades there.
Heavy snow has also affected US states including New York, Connecticut and Massachusetts, with school closed, transport systems drawn to a halt and residents told to stay at home.
Boston was said to be the worst hit with nearly 18in (45cm) of snow.
Sixteen deaths have been blamed on the wide-ranging storm, according to the Associated Press news agency.
A salt storage worker was killed in Philadelphia when a 100-ft (30-metre) pile of road salt fell and crushed him. A woman suffering from Alzheimer's disease in New York state froze to death after she wandered away from her rural home.
Some 1,200 flights were cancelled across the US and about 6,000 flights delayed on Saturday, according to reports. This followed more than 4,000 cancellations earlier in the week.
Chicago's O'Hare International Airport and Newark Liberty International Airport in New Jersey were said to be among the worst affected.
Environment Canada issued a special warning about heavy snow for much of Ontario on Sunday.
It said "widespread dangerous wind chills" were likely across the region in the first half of the week.
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