
The sun will soon set on summer, but will Ontario's heat ever end?
With the official start of autumn looming and summer temperatures still in place across southern Ontario this week, extending the patio season for a little longer, when will the heat relent?
For at least the next two weeks, warmer-than-normal temperatures will continue to dominate across most of Canada, with some exceptions.
Most regions will see an extended stretch of pleasant, late-summer-like weather, which is what southern Ontario is currently experiencing this week...for a few more days.
Visit our Complete Guide to Fall 2025 for an in depth look at the Fall Forecast, tips to plan for it and much more!
The gorgeous weather will continue through Thursday with abundant sunshine and above-seasonal temperatures. Thursday will be the warmest day of the week for the Greater Toronto Area (GTA) with widespread values in the upper 20s.
However, the warmth shall briefly disappear in time for the start of the weekend, with a cold front expected to bring the region back to reality. But the warm temperatures will return by Sunday, and continue next week.
Chance for mid-September 30 degrees this week before weekend cooldown

A ridge of high pressure over the Great Lakes may bring a chance for a 30-degree day this week, somewhere in southern Ontario.
Under a full sun and calm winds, high 20s are forecast by the late afternoon on Thursday.
Inland regions in the southwest, including Windsor and London, and the GTA, may reach, if not approach, 30°C on Thursday, which is when the heat will peak.

A cold front from northern Ontario will swing its way south, with minimal, spotty showers, but a noticeable cooldown for the weekend.
Friday and Saturday may be near to below seasonal for the GTA, Ottawa and southwestern sections, with chilly mornings dipping to near 10°C.
Much warmer weather will surge northeast across the region on Sunday, with widespread, mid-20 values, but cooler near Lake Ontario. Upper 20s are forecast for southwestern Ontario and parts of Niagara.

Warmer-than-normal temperatures will dominate for most of next week but there should be additional opportunities for showers and possibly a thunderstorm--helping to ease some of the current drought conditions in the region.
Wondering how the rest of the season will play out. Be sure to check out the official 2025 Fall Forecast for all of the details.