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An intense cold spell has seized a bitter and extended period of frigid weather, with temperatures hovering from 20 to 40 degrees below zero for weeks. On Tuesday, Braeburn in the Yukon recorded -55.7C, its coldest December temperature in half a century.

Enduring Chill in the Deep Minus Forties

Meanwhile, Mayo and Dawson endured over two straight weeks of nights dipping under the minus 40 Celsius threshold, with Mayo experiencing a low of -50.4C on Monday. Whitehorse also recorded a series of ten nights when the cold dipped under -30 Celsius.

The bitter chill extended its reach south over the festive period. In Edmonton, the Christmas overnight low dipped under -28 degrees Celsius.

Boxing Day was expected to bring minimum temperatures of at least minus 20C across many regions, from Edmonton in the west to Quebec in the east.

Forecast to Persist into the New Year

The frigid conditions are predicted to linger through the start of January. Authorities have cautioned about potential power failures in the Yukon over the next several days, as the system endures record-high pressure from peak power usage levels.

This extended freeze is the result of the polar vortex remaining anchored above Canadian territory through December, enabling a surge of icy Arctic winds to descend. The frigid dome is projected to gradually withdraw north gradually, enabling milder Pacific air to move across the United States and penetrate southern Canadian regions.

Dramatic Difference to American Heat

Meanwhile, in a dramatic contrast, areas of the United States saw 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 rather than the end of December.

Multiple states established new Christmas temperature highs. Oklahoma City, Oklahoma, reached 25 degrees Celsius on Christmas, 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.

Heat-Dome Effect Fuels Warmth

Above-average warmth is expected to continue on December 26th and into the weekend, with unseasonable heat forecast to sweep through the American Southeast soon.

The warmth has been fuelled by a powerful high-altitude ridge reaching from the arid southwest across the continent, creating a heat-dome effect. This pattern establishes a broad area of high pressure across much of the continent, 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.