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An intense cold spell has seized a severe and lengthy Arctic outbreak, with thermometers lingering between -20C and -40C for multiple weeks. On Tuesday, Braeburn in the Yukon recorded -55.7C, its coldest December temperature since 1975.

Enduring Chill Below -40C

Meanwhile, Mayo and Dawson endured 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. The capital, Whitehorse, likewise saw a series of ten nights when the cold dipped under -30 Celsius.

This Arctic air mass pushed further southward during the holiday season. On Christmas Day, overnight temperatures in Edmonton fell below -28C.

The day after Christmas was forecast to deliver lows of at least -20C through a wide swath, encompassing cities from Edmonton to Quebec.

Likely to Linger Through Early January

This harsh winter weather is expected to continue 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 historically high electricity consumption.

The prolonged chill has been caused by the polar vortex remaining anchored over Canada for much of December, which funnels frigid northern air southward. In the coming week, forecasts indicate this cold air will pull back northward allowing more temperate air from the Pacific to sweep across the US and into parts of southern Canada.

Dramatic Difference with US Warmth

Meanwhile, in a dramatic contrast, areas of the United States saw their warmest Christmas Day on record as the mercury climbed roughly 15 to 30 degrees above typical averages. In many areas, conditions felt more typical of April or May rather than the end of December.

Several states set Christmas Day temperature records. In Oklahoma, Oklahoma City hit 25C on Tuesday, topping the prior high mark of 22 degrees established over forty years ago. Cities including Austin and Dallas, in Texas, and Charlotte, North Carolina also logged readings above 25 degrees Celsius.

High-Pressure System Fuels Warmth

Above-average warmth is expected to continue 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 robust atmospheric ridge extending from the desert south-west towards the north and east, establishing a classic heat-dome pattern. This pattern establishes a broad area of high pressure blanketing a significant part of the landmass, effectively capping warm air at lower altitudes. Descending air compresses and adiabatically warms, fostering the buildup of exceptional warmth.