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Plunging into the coldest weather since May in southern Ontario

Tuesday, October 27th 2020, 9:20 pm - An unsettled pattern continues across Ontario as we keep an eye on some late week tropical influence AND some wet snow.

Though it's certainly felt like southern Ontario has been on the receiving end of the typical autumn chill, low temperatures actually haven't fallen below freezing in some of the major cities like Toronto and Hamilton. That'll change this week however, as a shift in the pattern has colder air marching east, bringing some of the coolest conditions since May. Forecasters are also keeping a close eye on tropical influence from Zeta, which could see some moisture nudging into the region later this week. More on the timing and how cold things get, below.


  • Broad upper trough over the Great Lakes maintains instability over the region
  • Remnant moisture from Zeta may clip extreme southern areas on Thursday, chance for some mixing and wet snow as temperatures plunge
  • Coldest conditions since May by Friday, warmer temperatures return for November

It's been tough keeping track of exactly which season it is across southern Ontario, especially after daytime highs soared into summer-like values on Friday, followed by severe thunderstorms, which produced an October tornado.

A shift in the weather pattern was inevitable however, as the frigid air that's been locked up over the Prairies begins its trek east throughout this week.


Zeta will make a second landfall along the central Gulf Coast by Wednesday night and then continue to track to the northeastern U.S. Thursday and Friday.

The latest forecast has now trended for Zeta remnants to stay further south, in terms of the moisture, so it looks less likely that southern Ontario will be impacted by rain or a rain-snow mix by Friday. The moisture may just scrape the Niagara region.

This will be a forecast that will be monitored closely in the next 24 hours.


A few flakes of wet snow could also mix in late Thursday night, with temperatures significantly cooling across the region. Overnight lows will be below freezing in the GTA, but not in the Niagara area, where the moisture could be situated. While no accumulation is expected, some of the higher terrain south of the border could see some major snow.


As the wet snow tapers through Friday morning, clouds will give way to sunshine from west to east across southern Ontario. Blustery conditions however, marked with a gusty north wind, will bring the coldest air of the season so far.


Overnight lows on Friday will dip below freezing, the first time for major cities including Toronto and Hamilton. In fact, a low temperature of -3°C hasn't been reported at Toronto's Pearson Airport since May 13 of this year.

Temperatures will rebound slightly into Saturday, making for a sunny, but still chilly, Halloween day.

MUST SEE: This fall frost pattern doesn't make any sense, Canada


By Sunday, the next system and trailing cold front is set to cross the region with a period of rain showers that will end as snow flurries, especially north of the Greater Toronto Area.

"Bands of lake-effect snow will develop southeast of Georgian Bay and Lake Huron with several centimetres of snow likely Sunday night and into early Monday," Gillham warns.

Next week will start on another cold note, but a decent warm-up is likely by the end of the week and for the first November weekend.

"An extended period of near to above seasonal temperatures are expected through the second week of November with temperatures more typical of mid-October," adds Gillham.

Be sure to check back for the most up-to-date weather in your area

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