Rain, thunderstorms kick off final week of May in southern Ontario

A chance for multiple rounds of rain and thunderstorms will be what kicks off the final week of May

Southern Ontario was treated to a well-deserved break during the day Sunday as storms stayed south of the border, allowing the soil and ground to dry out after rounds of storms crossed many regions over the past several days.

It was be a good day for a round of golf, a hike or walk, yard work or other outdoor activities, with abundant sunshine and warm temperatures in place across the region.

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That all changed Sunday night when a potent stateside low-pressure system moved into southwestern Ontario, bringing rain and a thunderstorms –– marking the start of a cooler, more unsettled pattern as we head into the final days of May. The unsettled system also prompted a marine tornado warning over Lake Erie Sunday evening.

Storms possible into Monday morning

A classic Colorado low spawning ample severe weather south of the border this weekend will move into the Great Lakes region late Sunday evening.

The first wave of rain will push over southwestern Ontario Sunday evening, and will include a chance of thunderstorms. Parts of the region, including the Windsor and Sarnia areas, could see severe storms, with the threat of large hail (nickel-sized or greater), heavy downpours and strong wind gusts up to 80 km/h. The storms should weaken considerably as they push eastward into the night.

A second push of rain and storms will move into the region after midnight and into the pre-dawn hours on Monday. Thunderstorms could reach farther north than they did overnight, with thunder possible around Toronto and Hamilton as the Monday morning commute begins. As the morning carries on, storms will continue to move eastward.

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Southern Ontario Monday am precipitation forecast May 26 2024

While neither of the nighttime rounds of storms are expected to be severe, any stronger cells could produce small hail, gusty winds, and heavy downpours. Watch out for pooling water on roadways and prepare for a slower commute Monday morning.

Renewed storm risk bubbles up Monday afternoon

Monday afternoon will be when things start to get interesting. The threat for stronger, more organized storm development will increase in the afternoon hours as the low-pressure system moves up across Georgian Bay and into eastern Ontario.

While much of the atmospheric instability will have been used up by the morning's storms, strong upper-level winds could help organize strong updrafts and overcome the lack of instability needed for storms to develop.

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southern Ontario Monday pm precipitation forecast May 26 2024

While any tornado threat is low, it is also non-zero. We could see some rotating updrafts, but the deciding factor will be how the storm shapes up with the decreased instability in play.

By Monday evening, the severe storm threat will stretch from the eastern Greater Toronto Area up highways 401 and 7 into Ottawa, including Kingston, Cornwall, Bancroft, and even next door into southern portions of Montreal. Storms could also pop up east of Georgian Bay, although the risk for severe storms will be diminished there first.

Large hail, strong wind gusts, and heavy rainfall will be the predominant threats in any severe thunderstorms that develop in eastern Ontario Monday afternoon.

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Regions that see multiple thunderstorms over the next twenty-four hours do also have a chance of receiving over 50 mm of rainfall. Be on the lookout for localized flooding from the heavy rains and prepare for the possibility of power outages in areas that see high winds.

Southern Ontario Monday storm risk v2 May 26 2024

Forecasters will also watch to see if the risk for severe weather moves closer into the Greater Toronto Area.

Stay alert for rapidly changing conditions in your area, and have a plan in place to seek shelter if dangerous weather threatens.

Plenty of rain over the next week

Conditions will remain unsettled through the middle of the week as continuing rounds of showers swing through southern Ontario.

Eastern Canada rainfall forecast May 26 2024

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Most communities throughout the region will see 10-30 mm of rain over the next seven days, with amounts varying by location due to the scattered nature of the showers and storms.

Below-seasonal temperatures will dominate the final days of May and heading into the first week of June. Daytime highs will only reach the upper teens for most communities through Thursday, with sunshine for the latter half of the week pushing temperatures back toward the lower 20s.

Stay with The Weather Network for the latest on your stormy forecast across Ontario.

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