FREDERICTON — A mass of cold air that meandered south from the Arctic has sent temperatures plunging with wind chills making it feel like -40 Celsius or colder from New Brunswick to eastern Alberta.
Arctic cold occasionally invades the southern latitudes for a few days before retreating north, bringing with it shivering temperatures, Peter Kimbell, meteorologist with Environment Canada, said Monday in an interview.
"We have permanently cold air parked across the Arctic .... From time to time, a pool of cold air meanders southward, and basically affects areas that are further south. And when that happens, people colloquially call it a polar vortex," Kimbell said.
Extreme cold warnings are in effect across the country, with temperatures feeling like -40 C in parts of Alberta, -45 C in Saskatchewan, and down to -50 C in parts of Manitoba and northern Ontario.
Thresholds for extreme cold warnings vary across the country, based on geography, Kimbell said. As an example, the threshold for extreme cold in Toronto is -30 C, he said. But if that same threshold is used for northern Ontario, the region would be under a cold warning almost all winter.
Parts of Canada can start to see some "moderation" in temperatures by Tuesday, he said. "It's still going to be cold, but not to the extreme extent that we saw (Monday) morning."
January has been colder than normal over the southern Prairies and southwestern Ontario, but warmer than normal over much of northern Quebec and parts of Nunavut, Kimbell said.
"Last month was somewhat warmer than normal, pretty much across the board, and across the country," Kimbell said. "Likewise for November .... This would be probably the first sustained blast of cold air this wintertime."
Anais Orsi, assistant professor at University of British Columbia's department of Earth, ocean and atmospheric sciences, said cold spells happen when the jet stream becomes "very wavy." The jet stream is defined by Environment Canada as “a narrow band of strong winds about 10 kilometres above the Earth, marking the dividing line between warm and cold air masses.”
"Sometimes the jet stream goes kind of straight across the whole Northern Hemisphere, and we don't have a cold spell," Orsi said.
"Sometimes it gets very wavy, and there's this wave of cold air that goes deep down into Canada. And then when that happens, usually the west is warm and the east is cold, or vice versa. Or maybe most of Canada is cold, but then Alaska is very warm, like right now, and maybe Greenland is warm. It's like a wave."
It's difficult to say whether climate change is causing fewer extreme cold spells, Orsi noted. They're relatively rare, she added, depriving researchers of data needed to study the phenomenon. One thing that scientists know for sure is that winters won't be as cold anymore, she said.
"We don't know whether we will have cold air outbreaks more or less often in the future, but we know that they will not be as cold."
Some parts of the country saw a snow dump before frigid air enveloped the area. Meteorologist Jill Maepea said a weather system that developed over the United States eastern seaboard brought about 25 centimetres of snow by Monday morning to southern New Brunswick, and about 15 cm to parts of Prince Edward Island.
Several schools across the Prairies and the coast of Atlantic Canada were closed because of cold weather and snow. Parts of rural Manitoba shut schools because the wind chill in some places felt as cold as -50 C. In Regina, the wind chill dipped to -47 C but schools in the city remained open; however, bus service was cancelled.
In New Brunswick, several anglophone and francophone schools were closed on Monday because of cold weather that made it feel like -35 C to -40 C.
Police across regions affected by extreme weather are asking people to avoid non-essential travel, dress warmly outside, ensure their fuel tank is full, and carry in their cars a winter driving survival kit with items such as a shovel, blanket, and booster cables.
The City of Toronto said it will deploy additional street outreach teams to perform wellness checks and encourage people living outside to find a spot indoors. Outreach staff will also hand out blankets, sleeping bags and warm winter clothing all winter long, it said.
This report by The Canadian Press was first published Jan. 20, 2025.
Hina Alam, The Canadian Press