The Great Lakes’ winter superpower is fading, polar vortex punches through
The Great Lakes lose their shield as an Arctic blast targets Ontario with the coldest weather of the year
Frigid Arctic air will grip Ontario for the remainder of January, with significantly reduced, lake-effect moderation. In some regions, temperatures could reach their coldest levels in over a decade by this weekend!
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Throughout winter, Arctic air frequently surges south across the Great Lakes. Typically, the warmer lake waters act as a buffer, releasing heat into the atmosphere and moderating surface temperatures, aiding southern Ontario and the Greater Toronto Area (GTA) in avoiding extreme cold. This often leaves areas like Ottawa and the U.S. Upper Midwest experiencing far colder conditions under the same winter air masses.
This time, however, the Great Lakes’ protective effect will diminish. Multiple Arctic air outbreaks this season have significantly cooled lake surface temperatures.
As a result, substantial ice cover is forming this week, limiting the lakes’ ability to warm the air above and sharply reducing their moderating impact.
This weekend, a lobe of the polar vortex will descend over Ontario, bringing the coldest air of the year across the province.
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Daytime highs will struggle in many regions, with morning and evening temperatures plunging into the -20s, and widespread wind chills ranging from -20 to -30.
Saturday highs and records to watch:
-15°C in Toronto and Hamilton (coldest highs since 2019)
-21°C in Ottawa (coldest since 2014)
-16°C in London (coldest since 2019)
-21°C in North Bay (coldest since 2019)
-21°C in Sault Ste Marie Friday (coldest since 2015, and could be the longest stretch below -10°C in 30 years
-25°C in Timmins on Friday (coldest since 2019)
Plan for extremely cold conditions across much of Ontario.