A summer surge arrives in southern Ontario
Southern Ontario is finally beginning to feel like summer, with temperatures rising and the first 30°C (86°F) readings of the season making an appearance. After a chilly and erratic May, the region is poised for its warmest spell of the year so far, with cities like Toronto, Ottawa, and even Montreal approaching or slightly surpassing the 30-degree mark by Wednesday, June 4.
Windsor, in fact, already joined the exclusive 30-degree club on Tuesday, June 3, clocking in at a scorching 30.1°C (86.2°F). This milestone has been long-awaited, as spring 2025 has been markedly colder than seasonal norms.
Humidity spikes and hazy skies
The heat wave is being fuelled by a moist, unstable air mass moving across southern and eastern Ontario, pushing humidex values into the low-to-mid 30s (86°F to 95°F). For many residents, even a brief walk outdoors will feel intense due to the mugginess and lack of strong breezes.
However, not all regions may get to enjoy the full heat potential. Lingering wildfire smoke continues to drift over much of southern Ontario, including the Greater Toronto Area (GTA). This aerosol haze can act like a shield, blocking solar radiation and capping surface temperatures, potentially keeping some areas just below the anticipated 30°C threshold.
Thunderstorms and showers on the way
Although early Wednesday morning could bring a clear and balmy start, change is already brewing. A low-pressure system is forecast to arrive by late Wednesday into Thursday, carrying with it a round of widespread showers and the potential for thunderstorms.
This midweek rainfall will serve as a temporary cooldown, a reminder that early June weather in Ontario remains fluid and volatile, even as summer tries to take hold.
Outlook for Ontario and beyond
The broader June forecast for Canada still highlights major heat events, including the formation of a heat dome and the development of a ring of fire storm track, which may trigger episodic severe weather. For now, though, residents across Ontario can look forward to at least a short-lived burst of summer heat, before conditions shift again.
Stay tuned to The Weather Network and your local forecast centres for ongoing updates on the evolving conditions.
