Ontario storm risk lingers as humidity fuels more downpours

Forecast CentreThe Weather Network

Published on Jul. 1, 2025, 12:22 AM

A humid air mass sparked storms and flooding in southern Ontario, with more activity expected through Tuesday.

Southern Ontario was battered with moisture-laden thunderstorms Monday, as an upsurge of humid air collided with an approaching cold front, resulting in downpours, gusty winds and localized damage—including reports of a tornado near Lucan, Ont., along Highway 4.

Lucan, Tornado, Storm, Thunderstorm, Wind, Rain, Ontario, June 30, 2025. (The Weather Network/Dave Sills)

Rainfall totals reached 21 mm in Point Pelee, 20 mm in Sarnia and 10 mm in Albion Hills. The stormy pattern is expected to continue into early this week, with thunderstorms looming across the region.

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Isolated storms linger through Tuesday

Isolated storms were expected to persist through Monday night, drawing energy from the moisture-rich air ahead of the Canada Day cold front.

Thunderstorm, Canada Day, Forecast, Rain, Wind, June 30, 2025. (The Weather Network/Tyler Hamilton)

Storms are expected to pick up along and south of Highway 401 on Tuesday, with heavy rain and lightning possible.

While most storms are not expected to be severe, there is still a risk of localized flooding, small hail and gusty winds, particularly for campers and those near waterways.

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Canada Day, Precipitation, Forecast, Rain, Wet, Storm, June 30, 2025. (The Weather Network/Tyler Hamilton)

Conditions in the Greater Toronto Area should clear in time for evening fireworks, whereas Ottawa may experience morning showers and embedded storms before gradually improving by late afternoon.

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Mid-week brings lake-breeze storms, upper trough

Looking ahead, isolated lake-breeze thunderstorms are likely in parts of southwestern Ontario on Wednesday and Thursday, particularly north of Lake Erie and Ontario.

An upper-level trough is also expected to move through early Thursday, bringing more showers and storms to Quebec.

Ontario, Forecast, Canada Day, Rain, Thunderstorm, Lightning, June 30, 2025. (The Weather Network/Tyler Hamilton)

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Weather models have increased their confidence in thunderstorm activity in the GTA through Tuesday evening, highlighting the value of residents remaining alert to rapidly shifting conditions and having contingency plans ready.