Ontario will see another taste of summer heat—but there's a catch

Heat and humidity are building across Ontario, but hazy skies and approaching showers, with a thunderstorm risk, may dampen the summer-like vibes.

After weeks of waiting, many in southern Ontario may soon be shedding their jackets--but it may not be all sunshine and blue skies.

For the first time this year, cities such as Toronto, Ottawa and even Montreal, Que., are expecting daytime temperatures near or above 30°C on Wednesday. Windsor, Ont., reached the 30-degree club on Tuesday, reaching 30.1°C.

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It's a summer milestone that has been visibly lacking so far in 2025, with prolonged, chilly temperatures putting May well below seasonal levels over much of the region.

30-degree club in Canada 2025 (updated June 3)

A warm, muggy air mass is expected to move in throughout southern and eastern Ontario beginning Tuesday, driving humidex values into the low to mid-30s, making even short walks outside feel like a workout.

30°C highs are on the horizon, but haze may spoil the party

While the heat seems encouraging, it is not guaranteed for everyone. One twist in the forecast is the lingering smoke from wildfires. 

If the smoke is thick enough, it could stop some of the sun's energy from reaching the surface, keeping temperatures just below the coveted 30-degree mark--particularly in parts of the Greater Toronto Area (GTA).

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However, for many, this may be their first true taste of summer after a chilly and unpredictable spring.

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With light winds and little cloud cover to begin the week, early Wednesday is shaping up to be the warmest stretch Ontario has seen this year thus far.

Rain turns up by midweek, giving a quick cooldown

But don't put your umbrella away just yet. A shift in the pattern is expected between late Wednesday and Thursday. 

A rain system is expected to move in, bringing widespread showers to potentially end the brief bout of heat.

Aerosol Concentration, Ontario, Quebec, Canada, Hot, Summer, June 2, 2025. (The Weather Network/Rachel Modestino)

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It serves as a reminder that, while summer is finally here, it isn't quite ready to stay just yet.

Continue to follow The Weather Network for the latest weather updates across Ontario.