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An intense cold spell has seized a severe and lengthy Arctic outbreak, with thermometers lingering between -20C and -40C for multiple weeks. On Tuesday, Braeburn in the Yukon recorded -55.7C, marking its chilliest December reading in nearly five decades.

Prolonged Freeze in the Deep Minus Forties

Meanwhile, Mayo and Dawson endured over two straight weeks of nights dipping under the minus 40 Celsius threshold, with Mayo experiencing a low of -50.4C earlier this week. Whitehorse also recorded a series of ten nights when readings fell to minus 30 degrees or lower.

This Arctic air mass pushed further southward during the holiday season. Christmas night saw Edmonton's temperatures plummet below minus 28C.

December 26th was anticipated to usher in minimum temperatures of at least minus 20C through a wide swath, including Edmonton, Montreal, Ottawa and Quebec.

Forecast to Persist Through Early January

This harsh winter weather is expected to continue through the start of January. Authorities have cautioned about potential power failures in the Yukon soon, as the territory’s power grid comes under strain from record-high energy demand.

The lengthy cold snap originates from a stationary polar vortex 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 gradually, enabling milder Pacific air to move across the US and into parts of southern Canada.

Dramatic Difference with US Warmth

Meanwhile, in a dramatic contrast, areas of the United States saw the hottest December 25th in their history as readings skyrocketed 15 to 30 degrees Celsius above normal. In many areas, conditions felt more typical of April or May rather than the end of December.

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. 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 atypical high temperatures expected to spread through the American Southeast soon.

This heat is being driven by a powerful high-altitude ridge extending from the desert south-west towards the north and east, which generates a heat-dome phenomenon. This pattern establishes a broad area of high pressure across much of the continent, effectively capping warm air at lower altitudes. As air sinks through the atmosphere, it compresses and heats further, enabling abnormally high temperatures to develop.