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An intense cold spell has seized an intense and prolonged cold spell, with readings persisting between -20C and -40C for weeks. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, representing its most frigid December day in half a century.

Enduring Chill in the Deep Minus Forties

Similarly, the communities of Mayo and Dawson experienced over two straight weeks of nights dipping under the minus 40 Celsius threshold, with the temperature in Mayo bottoming out at -50.4 degrees Celsius on Monday. Whitehorse similarly reported 10 nights when the cold dipped under -30 Celsius.

The deep freeze spread farther south during the holiday season. Christmas night saw Edmonton's temperatures plummet below minus 28C.

December 26th was anticipated to usher in lows of at least -20C across many regions, encompassing cities from Edmonton to Quebec.

Forecast to Persist into the New Year

The severe cold is forecast to persist into the new year. There are warnings of possible electrical grid strain in Yukon territory over the next several days, as the territory’s power grid comes under strain from historically high electricity consumption.

This extended freeze is the result of the Arctic vortex settling over Canada for much of December, which funnels frigid northern air southward. Next week, the cold air mass is expected to retreat north gradually, enabling milder Pacific air to move across the United States and penetrate southern Canadian regions.

Dramatic Difference Compared to Stateside Temperatures

In stark contrast, parts of the US experienced the hottest December 25th in their history as temperatures soared about 15-30C above the seasonal average. Across wide regions, the atmosphere was more akin to late spring than late December.

A number of states broke historical records for December 25th warmth. The capital of Oklahoma soared to 25C on Christmas Day, surpassing the previous peak of 22C set in 1982. Cities including Austin and Dallas, in Texas, and Charlotte, North Carolina also logged readings above 25 degrees Celsius.

High-Pressure System Sustains High Temperatures

Above-average warmth is expected to continue through Boxing Day and the days ahead, with abnormal warmth projected to move across the southeastern US in the coming days.

The warmth has been fuelled by a strong upper-level ridge extending from the desert south-west towards the north and east, creating a heat-dome effect. This setup creates an extensive zone of high atmospheric pressure over a large portion of North America, trapping warm air near the surface. As air sinks through the atmosphere, it compresses and heats further, allowing unusually warm temperatures to build.