Environment Canada has issued a wind chill warning for the city of Thunder Bay and surrounding areas.
A high of –22 C is expected Sunday, but it will feel more like –40 C with wind chill.
At 9 a.m. Sunday, the temperature observed at Thunder Bay airport was –34 C, but the wind chill made it feel like –45 C.
According to the warning posted on Environment Canada's website, "Another blast of Arctic air is invading northwestern Ontario."
'Polar arctic vortex'
Meteorologist Glenn Robinson said a "polar arctic vortex" originating in the Northwest Territories is hovering over northwestern Ontario.
"Some of the coldest air on the continent — or in the world — has actually settled down over our region," he said.
The weather service warns that in such conditions, exposed skin can freeze in less than five minutes.
The extreme cold is expected to last until Tuesday.
"The good news is that starting on Wednesday, and particularly once we get into later in the week, we are going to start to see moderating temperatures," said Robinson, noting that the extended forecast calls for a high of –2 C on Saturday.
"It'll feel quite balmy to most people."