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Northern Canada has been gripped by a bitter and extended period of frigid weather, with temperatures hovering between -20C and -40C for weeks. On Tuesday, Braeburn in the Yukon recorded -55.7C, marking its chilliest December reading since 1975.

Consecutive Nights Below -40C

Similarly, the communities of Mayo and Dawson experienced over two straight weeks of nights below -40C, with the temperature in Mayo bottoming out at -50.4 degrees Celsius earlier this week. The capital, Whitehorse, likewise saw a series of ten nights when temperatures dropped below -30C.

This Arctic air mass pushed further southward over the festive period. In Edmonton, the Christmas overnight low dipped under -28 degrees Celsius.

Boxing Day was expected to bring lows of at least -20C in numerous areas, from Edmonton in the west to Quebec in the east.

Expected to Continue Through Early January

This harsh winter weather is expected to continue into the new year. There are warnings of possible electrical grid strain in Yukon territory in the coming days, as its energy infrastructure faces unprecedented demand from historically high electricity consumption.

The prolonged chill has been caused by the polar vortex remaining anchored across the northern part of the continent this month, which funnels frigid northern air southward. In the coming week, forecasts indicate this cold air will pull back northward allowing more temperate air from the Pacific to sweep across America and reach into portions of southern Canada.

Stark Contrast to American Heat

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. 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. Oklahoma City, Oklahoma, reached 25 degrees Celsius on Christmas, topping the prior high mark of 22 degrees established over forty years ago. Cities including Austin and Dallas, in Texas, and Charlotte, North Carolina similarly saw thermometers rise past the 25C mark.

Heat-Dome Effect Drives the Heat

Warmer-than-normal conditions are forecast to last on December 26th and into the weekend, 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 reaching from the arid southwest across the continent, creating a heat-dome effect. This pattern establishes a broad area of high pressure blanketing a significant part of the landmass, which holds warm air close to the ground. Descending air compresses and adiabatically warms, fostering the buildup of exceptional warmth.