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A prolonged deep freeze has enveloped an intense and prolonged cold spell, with thermometers lingering from 20 to 40 degrees below zero for an extended duration. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, its coldest December temperature in half a century.

Consecutive Nights of Extreme Cold

In addition, the locales of Mayo and Dawson suffered through sixteen nights in a row below -40C, with the temperature in Mayo bottoming out at -50.4 degrees Celsius on Monday. Whitehorse similarly reported a series of ten nights when the cold dipped under -30 Celsius.

The bitter chill extended its reach south over the festive period. Christmas night saw Edmonton's temperatures plummet below minus 28C.

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

Expected to Continue Through Early January

The frigid conditions are predicted to linger into the new year. There are warnings of possible electrical grid strain in Yukon territory in the coming days, as the system endures record-high pressure from record-high energy demand.

The prolonged chill has been caused by the Arctic vortex settling across the northern part of the continent this month, enabling a surge of icy Arctic winds to descend. Next week, the cold air mass is expected to retreat north allowing more temperate air from the Pacific to sweep across the United States and penetrate southern Canadian regions.

Dramatic Difference with US Warmth

In stark contrast, parts of the US experienced their warmest Christmas Day on record as temperatures soared about 15-30C above the seasonal average. In many areas, conditions felt more typical of April or May instead of the heart of winter.

A number of states broke historical records for December 25th warmth. The capital of Oklahoma soared to 25C on Christmas Day, exceeding the old record of 22C from 1982. Urban centers like Austin, Dallas, and Charlotte, North Carolina similarly saw thermometers rise past the 25C mark.

Heat-Dome Effect Drives the Heat

Unseasonable heat is predicted to persist for the remainder of the week and beyond, with atypical high temperatures expected to spread across the southeastern US in the coming days.

This heat is being driven by a robust atmospheric ridge extending from the desert south-west towards the north and east, which generates a heat-dome phenomenon. Such a configuration results in a widespread high-pressure system over a large portion of North America, which holds warm air close to the ground. As air sinks through the atmosphere, it compresses and heats further, allowing unusually warm temperatures to build.