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A prolonged deep freeze has enveloped an intense and prolonged cold spell, with readings persisting from 20 to 40 degrees below zero for weeks. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, representing its most frigid December day in half a century.

Prolonged Freeze Below -40C

Similarly, the communities of Mayo and Dawson experienced 16 consecutive nights colder than minus 40 degrees, with Mayo experiencing a low of -50.4C earlier this week. Whitehorse also recorded a series of ten nights when temperatures dropped below -30C.

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

Boxing Day was expected to bring minimum temperatures of at least minus 20C through a wide swath, encompassing cities from Edmonton to Quebec.

Likely to Linger For Days to Come

This harsh winter weather is expected to continue into the new year. There are warnings of possible electrical grid strain in Yukon territory over the next several days, as the system endures record-high pressure from historically high electricity consumption.

This extended freeze is the result of a stationary polar vortex over Canada for much of December, allowing bitter Arctic air to spill south. In the coming week, forecasts indicate this cold air will pull back northward gradually, enabling milder Pacific air to move 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 the hottest December 25th in their history as temperatures soared about 15-30C above the seasonal average. In many areas, conditions felt more typical of April or May than late December.

Multiple states established new Christmas temperature highs. Oklahoma City, Oklahoma, reached 25 degrees Celsius on Christmas, surpassing the previous peak of 22C set in 1982. Urban centers like Austin, Dallas, and Charlotte, North Carolina were also among those that recorded temperatures above 25C.

High-Pressure System Fuels Warmth

Warmer-than-normal conditions are forecast to last through Boxing Day and the days ahead, with unseasonable heat forecast to sweep through the American Southeast soon.

The warmth has been fuelled by a robust atmospheric ridge stretching from the southwestern deserts northward and eastward, establishing a classic heat-dome pattern. Such a configuration results in a widespread high-pressure system blanketing a significant part of the landmass, trapping warm air near the surface. Sinking atmospheric air undergoes compression and additional heating, allowing unusually warm temperatures to build.