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A prolonged deep freeze has enveloped a severe and lengthy Arctic outbreak, with thermometers lingering in the minus 20 to minus 40 Celsius range for weeks. On Tuesday, Braeburn in the Yukon recorded -55.7C, representing its most frigid December day in nearly five decades.

Prolonged Freeze of Extreme Cold

Meanwhile, Mayo and Dawson endured over two straight weeks of nights dipping under the minus 40 Celsius threshold, with Mayo plunging to -50.4C at the start of the week. Whitehorse also recorded 10 nights when readings fell to minus 30 degrees or lower.

The bitter chill extended its reach south over the festive period. On Christmas Day, overnight temperatures in Edmonton fell below -28C.

Boxing Day was expected to bring lows of at least -20C across many regions, including Edmonton, Montreal, Ottawa and Quebec.

Forecast to Persist Through Early January

The severe cold is forecast to persist through the start of January. There are warnings of possible electrical grid strain in Yukon territory soon, as the territory’s power grid comes under strain from historically high electricity consumption.

This extended freeze is the result of a stationary polar vortex over Canada for much of December, enabling a surge of icy Arctic winds to descend. In the coming week, forecasts indicate this cold air will pull back northward slowly, permitting warmer Pacific winds to flow over the US and into parts of southern Canada.

Stark Contrast with US Warmth

Meanwhile, in a dramatic contrast, areas of the United States saw the hottest December 25th in their history as the mercury climbed roughly 15 to 30 degrees above typical averages. For numerous locations, the weather resembled a spring day in April or May rather than the end of December.

Multiple states established new Christmas temperature highs. The capital of Oklahoma soared to 25C on Christmas Day, topping the prior high mark of 22 degrees established over forty years ago. Urban centers like Austin, Dallas, and Charlotte, North Carolina also logged readings above 25 degrees Celsius.

High-Pressure System Drives the Heat

Above-average warmth is expected to continue for the remainder of the week and beyond, with abnormal warmth projected to move into the south-eastern states later in the week.

The unseasonable temperatures are powered by a strong upper-level 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 across much of the continent, which holds warm air close to the ground. Descending air compresses and adiabatically warms, enabling abnormally high temperatures to develop.