Toronto is finally on track to experience its first real blast of summer after an unusually long stretch without sustained heat. The city’s 270-day heat drought is coming to a close, setting the stage for a dramatic shift in the weather pattern.
Pattern flip in the second half of June
An amplifying upper ridge is expected to build over southern Ontario starting this weekend, peaking between Sunday, June 22 and Monday, June 23. As heat and humidity combine, humidex values are forecast to exceed 40 (over 104°F), marking a significant thermal escalation.
Highs will climb into the 30s (86°F) across parts of the region, and a streak of more than eight consecutive days above 25°C (77°F) is projected for Toronto — a pattern not seen since September 2024. Until now, the city has only managed two back-to-back 25°C days and a single 30°C reading on June 4.
Oppressive heat and tropical nights
This won’t just be hot — it will be oppressive. Overnight lows will remain above 20°C (68°F), offering little to no relief from the daytime heat. With much of the population still unaccustomed to summer warmth this year, the upcoming conditions may prove challenging, particularly for vulnerable individuals and those without air conditioning.
From heat drought to thunderstorm threats
The arrival of this heat wave will also bring a more unstable atmosphere, especially as we move into the middle of next week. As surface temperatures soar, the potential for late-day thunderstorms will increase. While these storms may briefly temper daytime highs, they won’t disrupt the overarching trend of a hotter-than-average June.
Ottawa to experience similar conditions
Ottawa hasn’t fared much better so far in 2025, with only three days above 25°C (77°F), from June 6 to 8. Like the rest of eastern Ontario, it too is bracing for a quick and intense warm-up that will feel like a sudden arrival of summer.
A long wait coming to an end
It’s been since September 2024 that Toronto recorded even three straight days over 25°C. But with the official start of summer on Friday, June 20, the heat is poised to settle in, delivering a genuine summertime stretch that’s been absent for more than nine months.
