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An intense cold spell has seized an intense and prolonged cold spell, with thermometers lingering from 20 to 40 degrees below zero for weeks. This week, the Yukon community of Braeburn saw the mercury drop to -55.7C, representing its most frigid December day since 1975.

Prolonged Freeze 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 at the start of the week. The capital, Whitehorse, likewise saw ten separate nights when readings fell to minus 30 degrees or lower.

This Arctic air mass pushed further southward during the holiday season. In Edmonton, the Christmas overnight low dipped under -28 degrees Celsius.

The day after Christmas was forecast to deliver readings no higher than -20 Celsius across many regions, including Edmonton, Montreal, Ottawa and Quebec.

Forecast to Persist For Days to Come

The frigid conditions are predicted to linger into the new year. Authorities have cautioned about potential power failures in the Yukon in the coming days, as its energy infrastructure faces unprecedented demand from peak power usage levels.

This extended freeze is the result of a stationary polar vortex across the northern part of the continent this month, allowing bitter Arctic air to spill south. In the coming week, forecasts indicate this cold air will pull back northward slowly, permitting warmer Pacific winds to flow over America and reach into portions of southern Canada.

Dramatic Difference Compared to Stateside Temperatures

In stark contrast, parts of the US experienced the hottest December 25th in their history as the mercury climbed roughly 15 to 30 degrees above typical averages. Across wide regions, the atmosphere was more akin to late spring rather than the end of 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. Urban centers like Austin, Dallas, and Charlotte, North Carolina similarly saw thermometers rise past the 25C mark.

Heat-Dome Effect Sustains High Temperatures

Warmer-than-normal conditions are forecast to last on December 26th and into the weekend, with atypical high temperatures expected to spread through the American Southeast soon.

The unseasonable temperatures are powered by a powerful high-altitude ridge reaching from the arid southwest across the continent, creating a heat-dome effect. 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. Descending air compresses and adiabatically warms, allowing unusually warm temperatures to build.