Polar vortex bringing frigid temperatures to Canada, U.S.

After a mild fall so far, temperatures have plunged dramatically in recent days across much of Western Canada, and now the cold will extend eastward this week because of a polar vortex.

Cold Arctic air to move across much of the continent this week

December temperatures are plunging across much of North America because of the circulation of cold air known as a polar vortex. (CBC)

After a mild fall so far, temperatures have plunged dramatically in recent days across much of Western Canada, and now the cold will extend to Eastern Canada this week because of a polar vortex.

Temperatures around –30 C combined with winds up to 15 km/hr led to extreme wind chill values of –40 or colder in southwestern Manitoba on the weekend.

Extreme cold warnings were in effect Sunday in central and northern Alberta, where temperatures dipped below  –20, with wind chill values near or below -40.

B.C.'s Central Coast and inland areas were expected to see a high of 0 on Sunday with a warning for wind chill values of -20 to -25, continuing Sunday through Monday morning. 

The polar vortex, a swirl of air moving counterclockwise, is drawing its cold air from a ridge of high pressure over the North Pacific and a second one over Western Europe, said Chris St. Clair of the Weather Network.

Arctic air slowly spilling south

"The two ridges are holding the cold in place. The cold air settles to the surface and very slowly is spilling to the south," he said.

Forecasters say the cold circulation of air will push down temperatures from -2 to -15 through the course of the week in the Lower Great Lakes and produce a wind chill of around -20 by Wednesday, with similar temperatures on Thursday in Montreal and Atlantic Canada.

In the interim, lake-effect snow coming off what Environment Canada is calling a "Colorado Low" is in the forecast Sunday afternoon for parts of southern Ontario. A total of 10 to 15 centimetres of snow is expected with westerly winds. Snow began over southwestern Ontario Sunday morning and the system was to reach eastern Ontario by late afternoon.

About 10 centimetres of snow was expected for Ottawa and Montreal on Monday morning. In Atlantic Canada, flurries and occasional snow squalls are expected over northern and western Cape Breton Sunday and Sunday night before gradually easing Monday morning.

The Arctic blast will hit the U.S. Midwest on Tuesday with the coldest temperatures of -12 C and lower in Minnesota.

Chicago's department of streets and sanitation is monitoring a storm system that was to move into northern Illinois later Sunday afternoon, bringing up to 27 centimetres of snow.

Up to a metre of snow has fallen in northeastern Ohio since Friday, weather forecasters said Sunday.

U.S. meteorologists have warned that December will deliver round after round of bitter cold to the majority of the United States. The plunging temperatures come after the warmest-ever October through November period for the Lower 48 states. 

With files from The Associated Press and Reuters