Toronto temperatures are going to swing by 16 C this week

With less than two weeks until the official start of fall, Toronto temperatures are slowly beginning to show signs of the seasonal shift, but it looks like summer isn't ready to let up quite yet.

As is the case during most Septembers, the city is in for a major temperature rollercoaster this week, with daytime highs reaching the mid-20s before plunging dramatically by as much as 16 C overnight.

According to Environment Canada's seven-day forecast, Toronto's daytime high on Thursday will reach 26 C before temperatures drop dangerously close to the single-digit territory tonight, when the nighttime low is expected to be 10 C.

Toronto's seven-day weather forecast. Photo: Environment Canada.

The warm afternoons will continue well into the weekend, with Friday's high expected to reach 23 C before falling to just 12 C overnight. On Saturday, temperatures could climb back up to 26 C, followed by a 10 C drop to 16 C overnight.

There will be another dramatic swing on Sunday, when temperatures drop from 26 C during the day to 13 C at night. Temperatures will enter a more consistent range on Monday, when the daytime high of 23 C will likely be followed by a low of 16 C.

Tuesday could once again see temperatures hit 26 C (though there's also a chance of showers), with temperatures dropping once again to 13 C overnight. In other words, you'll probably want to keep both your T-shirts and light jackets on hand throughout the rest of the week.

The dramatic day-to-night swings come just days before fall arrives in Ontario, and if you're secretly hoping for a slower transition into cooler weather, I've got good news for you.

The Weather Network released its 2026 fall forecast for Canada on Wednesday, which provides an early look at the weather patterns we can expect over the next few months. Overall, models suggest that most of Canada, including Ontario, is expected to record above-normal temperatures and below-normal precipitation this upcoming season.

That is, of course, thanks to a "supersized" El Niño that's now "firmly established" and has a 100 per cent likelihood of persisting through February 2027. The natural climate phenomenon only occurs every two to seven years and has the ability to significantly impact temperature and precipitation worldwide, despite being characterized as unusually warm ocean surface temperatures in the central and eastern equatorial Pacific. 

Looking at Ontario specifically, The Weather Network describes the province's fall personality as "unhurried," thanks to what could be an extended version of the season. Overall, fewer classic fall storms are expected in Ontario, although much of the period from mid-September through mid-October could stick close to seasonal temperatures.