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A prolonged deep freeze has enveloped an intense and prolonged cold spell, with thermometers lingering between -20C and -40C for an extended duration. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, representing its most frigid December day since 1975.

Consecutive Nights Below -40C

Similarly, the communities of Mayo and Dawson experienced over two straight weeks of nights colder than minus 40 degrees, with the temperature in Mayo bottoming out at -50.4 degrees Celsius at the start of the week. Whitehorse also recorded 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.

The day after Christmas was forecast to deliver minimum temperatures of at least minus 20C in numerous areas, including Edmonton, Montreal, Ottawa and Quebec.

Likely to Linger into the New Year

The frigid conditions are predicted to linger for the foreseeable future. There are warnings of possible electrical grid strain in Yukon territory in the coming days, as the territory’s power grid comes under strain from record-high energy demand.

The prolonged chill has been caused by the Arctic vortex settling across the northern part of the continent this month, which funnels frigid northern air southward. 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.

Dramatic Difference to American Heat

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 than late December.

Multiple states established new Christmas temperature highs. The capital of Oklahoma soared to 25C on Christmas Day, exceeding the old record of 22C from 1982. Cities including Austin and Dallas, in Texas, and Charlotte, North Carolina similarly saw thermometers rise past the 25C mark.

Heat-Dome Effect Drives the Heat

Warmer-than-normal conditions are forecast to last for the remainder of the week and beyond, with unseasonable heat forecast to sweep into the south-eastern states later in the week.

The warmth has been fuelled by a powerful high-altitude ridge extending from the desert south-west towards the north and east, which generates a heat-dome phenomenon. Such a configuration results in a widespread high-pressure system over a large portion of North America, which holds warm air close to the ground. Descending air compresses and adiabatically warms, fostering the buildup of exceptional warmth.