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A prolonged deep freeze has enveloped an intense and prolonged cold spell, with readings persisting from 20 to 40 degrees below zero for multiple weeks. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, marking its chilliest December reading in nearly five decades.

Prolonged Freeze of Extreme Cold

Meanwhile, Mayo and Dawson endured 16 consecutive nights colder than minus 40 degrees, with the temperature in Mayo bottoming out at -50.4 degrees Celsius earlier this week. Whitehorse similarly reported ten separate nights when temperatures dropped below -30C.

This Arctic air mass pushed further southward during the holiday season. Christmas night saw Edmonton's temperatures plummet below minus 28C.

Boxing Day was expected to bring readings no higher than -20 Celsius across many regions, including Edmonton, Montreal, Ottawa and Quebec.

Expected to Continue For Days to Come

This harsh winter weather is expected to continue into the new year. Authorities have cautioned about potential power failures in the Yukon in the coming days, as the system endures record-high pressure from historically high electricity consumption.

The prolonged chill has been caused by the polar vortex remaining anchored above Canadian territory through December, allowing bitter Arctic air to spill south. The frigid dome is projected to gradually withdraw north allowing more temperate air from the Pacific to sweep across the US and into parts of southern Canada.

Dramatic Difference Compared to Stateside Temperatures

Conversely, sections of America recorded historically high temperatures for Christmas as the mercury climbed roughly 15 to 30 degrees above typical averages. For numerous locations, the weather resembled a spring day in April or May instead of the heart of winter.

Several states set Christmas Day temperature records. The capital of Oklahoma soared to 25C on Christmas Day, topping the prior high mark of 22 degrees established over forty years ago. Urban centers like Austin, Dallas, and Charlotte, North Carolina were also among those that recorded temperatures above 25C.

Heat-Dome Effect Sustains High Temperatures

Above-average warmth is expected to continue through Boxing Day and the days ahead, with unseasonable heat forecast to sweep through the American Southeast soon.

The warmth has been fuelled by a strong upper-level ridge extending from the desert south-west towards the north and east, which generates a heat-dome phenomenon. This setup creates an extensive zone of high atmospheric pressure over a large portion of North America, which holds warm air close to the ground. As air sinks through the atmosphere, it compresses and heats further, enabling abnormally high temperatures to develop.