Tuesday is shaping up to be a stormy day in southern Ontario.

Environment Canada has issued an updated weather outlook, which says that two rounds of thunderstorms are expected to sweep through a large part of the region.

First round of storms

During the overnight hours, parts of southwestern Ontario from Goderich to Niagara, including portions of the Greater Toronto Area, are expected to get the hardest hit (location A on the map below).

“A first wave of thunderstorms will primarily affect this area with heavy rainfall being the main threat,” forecasters said.

“Up to toonie-size hail may be possible in the strongest storms.”

Up to 40 mm of rain is possible in those areas with the first round of storms, with local peak hourly rainfall of 20 to 30 mm, forecasters indicated.

Flash flooding, water pooling on roads, and washouts near rivers and creeks is possible.

Environment Canada

Areas from Wiarton towards Trenton (location B) may also see storms overnight, but it is less likely.

“The chance for thunderstorms lessens as you move northeast of the main A area, however thunderstorms are still possible along with heavy rain,” Environment Canada said.

Up to 25 mm is possible there, with a local peak hourly rate of 15 mm.

Far southwestern Ontario, including Windsor, (location C) could see storms early overnight, with up to 15 mm locally in total from the first round.

“During the onset of thunderstorms in the evening and early overnight, parts of this area may receive strong thunderstorms. Strong wind gusts and small hail may be possible,” the weather agency said for those areas.

Second round of storms may be ‘severe’

Come late Tuesday afternoon and evening, a large portion of southern Ontario, including the Greater Toronto Area, Hamilton, the Niagara Region, London, and Windsor (location A below) are expected to see a second round of storms.

“After a break in precipitation late Tuesday morning and early afternoon, a second round of thunderstorms is expected and may reach severe potential,” Environment Canada said.

“Up to 90 km/h (winds), up to toonie-size hail and heavy rain will be possible with these storms.”

Up to 30 mm of rain is possible locally with a peak hourly rate of 20 to 30 mm.

Environment Canada

Forecasters said the storms could result in downed trees, broken tree branches, flooding in low-lying areas, loose objects being tossed, and damage to weak buildings.

Meanwhile, areas from Wiarton towards Kingston are also expected to see storms, but those will have “a muted chance for severe potential.”

“Heavy rain is still likely with these storms,” Environment Canada said.

A peak local hourly rainfall amount of 15 to 25 mm is in the forecast there, with up to 25 mm in total from the second round.


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