MONTREAL (AFP) - Canada and the northern United States were suffering their first brutal cold spell of the season Friday (Dec 16), after a frigid mass of Arctic air - the dreaded "Polar Vortex" - settled over the region.
A week before the official start of winter, bone-chilling temperatures far more brutal than normal for this time of year were felt across Canada, as well as in parts of the US North and Midwest.
The cold snap was expected to deepen this weekend with the arrival of heavy snow, US meteorological services said.
The National Weather Service in Washington warned on Friday of "significant winter precipitation and dangerously cold wind chills to a large portion of the country through the weekend."
The cold comes courtesy of the Polar Vortex, a large area of high pressure and frigid temperatures that lingers around the North Pole and sometimes is carried via the jet stream into North America.
The phenomenon has existed for thousands of years, but only relatively recent has entered popular parlance.
It now is synonymous with prolonged spells of teeth-chattering, blood-curdling cold - the kind of weather Canada and the US are currently enduring.
"Heavy snow is forecast from the High Plains to the Great Lakes Friday, and this snow will spread into the Northeast on Saturday," the NWS said.
"Treacherous freezing rain is forecast across portions of the Ohio Valley, mid-Atlantic and New England."
Environment Canada said snow, which already is falling in some regions of the country, is expected in eastern Canada Saturday before turning into freezing rain and ice pellets.
Temperatures on Friday were already well below freezing throughout Canada, where residents of Calgary, Saskatoon and Winnipeg in the western prairies were bracing for lows of minus 21 deg C to minus 27 deg C.
In Quebec and the Maritimes provinces to the east, meanwhile, the mercury hovered around minus 20 deg C at midday, with a storm hammering the provinces of Nova Scotia and Newfoundland.
Even Canada's Pacific coast, which generally is spared frigid cold, has been subjected to snow and minus 7 deg C temperatures.
There have been two snowstorms in eastern Canada already this month, but temperatures have bounced back to near the freezing point.
"It's yo-yo kind of weather... where winter is trying to get a foothold, and sort of summery-like weather is still trying to hang on," Environment Canada meteorologist Dave Phillips told public broadcaster CBC.
Phillips said The worst is yet to come in terms of cold, in January and February, with a overall cooling expected after last year's relatively mild winter.