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A prolonged deep freeze has enveloped a severe and lengthy Arctic outbreak, with thermometers lingering between -20C and -40C for weeks. This week, the Yukon community of Braeburn saw the mercury drop to -55.7C, representing its most frigid December day in half a century.

Prolonged Freeze in the Deep Minus Forties

Meanwhile, Mayo and Dawson endured sixteen nights in a row dipping under the minus 40 Celsius threshold, with the temperature in Mayo bottoming out at -50.4 degrees Celsius earlier this week. Whitehorse similarly reported a series of ten nights when the cold dipped under -30 Celsius.

This Arctic air mass pushed further southward during the holiday season. Christmas night saw Edmonton's temperatures plummet below minus 28C.

Boxing Day was expected to bring minimum temperatures of at least minus 20C through a wide swath, from Edmonton in the west to Quebec in the east.

Expected to Continue into the New Year

The frigid conditions are predicted to linger into the new year. Officials have warned that the Yukon could face electricity outages soon, as the system endures record-high pressure from record-high energy demand.

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 United States and penetrate southern Canadian regions.

Stark Contrast with US Warmth

In stark contrast, parts of the US experienced the hottest December 25th in their history as readings skyrocketed 15 to 30 degrees Celsius above normal. 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, topping the prior high mark of 22 degrees established over forty years ago. Metropolitan areas such as Austin, Dallas, and Charlotte were also among those that recorded temperatures above 25C.

Heat-Dome Effect Sustains High Temperatures

Warmer-than-normal conditions are forecast to last through Boxing Day and the days ahead, 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 stretching from the southwestern deserts northward and eastward, which generates a heat-dome phenomenon. Such a configuration results in a widespread high-pressure system over a large portion of North America, effectively capping warm air at lower altitudes. Sinking atmospheric air undergoes compression and additional heating, allowing unusually warm temperatures to build.