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Northern Canada has been gripped by a severe and lengthy Arctic outbreak, 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.

Prolonged Freeze 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 similarly reported a series of ten nights when the cold dipped under -30 Celsius.

This Arctic air mass pushed further southward over the festive period. Christmas night saw Edmonton's temperatures plummet below minus 28C.

The day after Christmas was forecast to deliver readings no higher than -20 Celsius in numerous areas, from Edmonton in the west to Quebec in the east.

Forecast to Persist Through Early January

The severe cold is forecast to persist through the start of January. 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 historically high electricity consumption.

This extended freeze is the result of a stationary polar vortex above Canadian territory through 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 the US and into parts of southern Canada.

Pronounced Disparity with US Warmth

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 instead of the heart of winter.

A number of states broke historical records for December 25th warmth. In Oklahoma, Oklahoma City hit 25C on Tuesday, exceeding the old record of 22C from 1982. Metropolitan areas such as Austin, Dallas, and Charlotte similarly saw thermometers rise past the 25C mark.

Atmospheric Ridge 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 unseasonable temperatures are powered 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 over a large portion of North America, trapping warm air near the surface. Sinking atmospheric air undergoes compression and additional heating, enabling abnormally high temperatures to develop.