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An intense cold spell has seized a bitter and extended period of frigid weather, with readings persisting between -20C and -40C for multiple weeks. A reading of -55.7 Celsius was logged in Braeburn, Yukon, on Tuesday, its coldest December temperature since 1975.

Prolonged Freeze in the Deep Minus Forties

In addition, the locales of Mayo and Dawson suffered through sixteen nights in a row colder than minus 40 degrees, with Mayo experiencing a low of -50.4C earlier this week. The capital, Whitehorse, likewise saw 10 nights when readings fell to minus 30 degrees or lower.

The deep freeze spread farther south over the festive period. On Christmas Day, overnight temperatures in Edmonton fell below -28C.

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

Likely to Linger Through Early January

This harsh winter weather is expected to continue for the foreseeable future. Authorities have cautioned about potential power failures in the Yukon soon, as the system endures record-high pressure from historically high electricity consumption.

The prolonged chill has been caused by a stationary polar vortex above Canadian territory through December, allowing bitter Arctic air to spill south. In the coming week, forecasts indicate this cold air will pull back northward allowing more temperate air from the Pacific to sweep across the United States and penetrate southern Canadian regions.

Pronounced Disparity with US Warmth

Meanwhile, in a dramatic contrast, areas of the United States saw the hottest December 25th in their history 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. 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 also logged readings above 25 degrees Celsius.

Heat-Dome Effect Fuels Warmth

Unseasonable heat is predicted to persist through Boxing Day and the days ahead, with atypical high temperatures expected to spread through the American Southeast soon.

The warmth has been fuelled by a robust atmospheric ridge stretching from the southwestern deserts northward and eastward, establishing a classic heat-dome pattern. This pattern establishes a broad area of high pressure blanketing a significant part of the landmass, trapping warm air near the surface. Descending air compresses and adiabatically warms, allowing unusually warm temperatures to build.