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A prolonged deep freeze has enveloped an intense and prolonged cold spell, with thermometers lingering between -20C and -40C for weeks. On Tuesday, Braeburn in the Yukon recorded -55.7C, representing its most frigid December day since 1975.

Consecutive Nights Below -40C

In addition, the locales of Mayo and Dawson suffered through 16 consecutive nights below -40C, with Mayo plunging to -50.4C on Monday. Whitehorse also recorded a series of ten nights when the cold dipped under -30 Celsius.

The bitter chill extended its reach south through Christmas week. On Christmas Day, overnight temperatures in Edmonton fell below -28C.

The day after Christmas was forecast to deliver minimum temperatures of at least minus 20C in numerous areas, from Edmonton in the west to Quebec in the east.

Expected to Continue into the New Year

The severe cold is forecast to persist into the new year. 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.

This extended freeze is the result of the polar vortex remaining anchored across the northern part of the continent this month, 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.

Dramatic Difference to American Heat

Meanwhile, in a dramatic contrast, areas of the United States saw historically high temperatures for Christmas as temperatures soared about 15-30C above the seasonal average. Across wide regions, the atmosphere was more akin to late spring rather than the end of December.

Several states set Christmas Day temperature records. 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.

Atmospheric Ridge Sustains High Temperatures

Warmer-than-normal conditions are forecast to last through Boxing Day and the days ahead, with atypical high temperatures expected to spread into the south-eastern states later in the week.

The unseasonable temperatures are powered by a powerful high-altitude ridge reaching from the arid southwest across the continent, establishing a classic heat-dome pattern. Such a configuration results in a widespread high-pressure system across much of the continent, which holds warm air close to the ground. Sinking atmospheric air undergoes compression and additional heating, allowing unusually warm temperatures to build.