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A prolonged deep freeze has enveloped an intense and prolonged cold spell, with temperatures hovering between -20C and -40C for multiple weeks. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, representing its most frigid December day in nearly five decades.

Enduring Chill of Extreme Cold

Meanwhile, Mayo and Dawson endured over two straight weeks of nights colder than minus 40 degrees, with Mayo experiencing a low of -50.4C at the start of the week. Whitehorse similarly reported 10 nights when readings fell to minus 30 degrees or lower.

This Arctic air mass pushed further southward over the festive period. On Christmas Day, overnight temperatures in Edmonton fell below -28C.

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

Likely to Linger For Days to Come

The severe cold is forecast to persist through the start of January. Authorities have cautioned about potential power failures in the Yukon over the next several days, as the territory’s power grid comes under strain from record-high energy demand.

This extended freeze is the result of the polar vortex remaining anchored over Canada for much of December, allowing bitter Arctic air to spill south. The frigid dome is projected to gradually withdraw north slowly, permitting warmer Pacific winds to flow over America and reach into portions of southern Canada.

Stark Contrast Compared to Stateside Temperatures

Conversely, sections of America recorded their warmest Christmas Day on record as readings skyrocketed 15 to 30 degrees Celsius above normal. In many areas, conditions felt more typical of April or May instead of the heart of winter.

Multiple states established new Christmas temperature highs. In Oklahoma, Oklahoma City hit 25C on Tuesday, surpassing the previous peak of 22C set in 1982. Metropolitan areas such as Austin, Dallas, and Charlotte also logged readings above 25 degrees Celsius.

Heat-Dome Effect Sustains High Temperatures

Warmer-than-normal conditions are forecast to last for the remainder of the week and beyond, with unseasonable heat forecast to sweep across the southeastern US in the coming days.

This heat is being driven by a robust atmospheric ridge extending from the desert south-west towards the north and east, creating a heat-dome effect. This pattern establishes a broad area of high 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.