Frost and flurries: Major October cooldown hits southern Ontario early this week

A noticeably chilly pattern has descended over the Great Lakes, bringing the region some of its coldest temperatures since April. There's even the chance for snow flurries as temperatures drop, especially for higher elevations in parts of southern Ontario.

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You'll want to be sure to dress in layers, and cover up plants in any frost prone areas. A widespread frost advisory was issued early Tuesday morning, warning to take preventative measures to protect frost-sensitive plants and trees.

This won't be a free-fall right into winter conditions, however, as an extended period of much warmer and mostly dry weather will return on Thursday, and continue through the weekend and into next week.

Tuesday into Wednesday: Snow chances grow as temperatures plunge

Lake-effect showers snuck their way down from Georgian Bay and Lake Huron on Monday evening, with the risk continuing into Tuesday and Wednesday, as well. There was the chance for some areas in the escarpment up towards cottage country even seeing snow flurries on Tuesday morning.

Regions north of Orangeville along Highway 10, including Shelburne, are at the highest risk of seeing the first light accumulating snowfall of the season.

Baron - Precip predawn Wednesday ON
Baron - Precip predawn Wednesday ON

Lake-effect showers will continue through Wednesday, and once again it is possible for rain to change to snow as overnight temperatures dip down near zero for the same locations.

While it's unlikely for any significant snowfall totals across southern Ontario, with temperatures hovering a couple of degrees above freezing, the risk across the higher terrain is certainly there.

Baron - Snow accumulation - Oct15
Baron - Snow accumulation - Oct15

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Northerly winds will also help to keep temperatures unseasonably cold on Tuesday.

Temperatures will struggle to reach the double digits throughout the region, with even chillier readings expected beneath more organized precipitation across eastern portions of the province.

Ontario departure from normal highs Tuesday_Oct. 14
Ontario departure from normal highs Tuesday_Oct. 14

The last time we saw single-digit highs across southern Ontario include:

  • April 24 - Windsor

  • April 25 - Toronto, Hamilton

  • April 25 - Kingston

  • April 30 - Ottawa

Ontario's last single-digit highs in 2024
Ontario's last single-digit highs in 2024

If Toronto fails to hit 10°C Tuesday, it'll be our first day mired in the single digits since April 25. Ottawa is looking at its coldest day since April 5.

It’s not a pattern that will last, however, as there’s now a strong signal for above-seasonal temperatures beginning late week, with temperatures even spiking above 20°C.

This coming weekend looks exceptional for late-October standards, with a massive ridge of high pressure all across southern Ontario.

Stay with The Weather Network for all the latest on conditions across Ontario.

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