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An intense cold spell has seized a severe and lengthy Arctic outbreak, 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, its coldest December temperature in half a century.

Prolonged Freeze Below -40C

Similarly, the communities of Mayo and Dawson experienced sixteen nights in a row colder than minus 40 degrees, with Mayo experiencing a low of -50.4C at the start of the week. The capital, Whitehorse, likewise saw ten separate nights when the cold dipped under -30 Celsius.

The bitter chill extended its reach south during the holiday season. On Christmas Day, overnight temperatures in Edmonton fell below -28C.

December 26th was anticipated to usher in readings no higher than -20 Celsius in numerous areas, including Edmonton, Montreal, Ottawa and Quebec.

Forecast to Persist into the New Year

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 record-high energy demand.

This extended freeze is the result of a stationary polar vortex across the northern part of the continent this month, which funnels frigid northern air southward. Next week, the cold air mass is expected to retreat north gradually, enabling milder Pacific air to move across the United States and penetrate southern Canadian regions.

Stark Contrast Compared to Stateside Temperatures

In stark contrast, parts of the US experienced their warmest Christmas Day on record as the mercury climbed roughly 15 to 30 degrees above typical averages. Across wide regions, the atmosphere was more akin to late spring than late December.

A number of states broke historical records for December 25th warmth. Oklahoma City, Oklahoma, reached 25 degrees Celsius on Christmas, exceeding the old record of 22C from 1982. Cities including Austin and Dallas, in Texas, and Charlotte, North Carolina were also among those that recorded temperatures above 25C.

Atmospheric Ridge Sustains High Temperatures

Warmer-than-normal conditions are forecast to last for the remainder of the week and beyond, with abnormal warmth projected to move into the south-eastern states later in the week.

The warmth has been fuelled by a powerful high-altitude ridge extending from the desert south-west towards the north and east, creating a heat-dome effect. Such a configuration results in a widespread high-pressure system blanketing a significant part of the landmass, effectively capping warm air at lower altitudes. As air sinks through the atmosphere, it compresses and heats further, allowing unusually warm temperatures to build.