The conditions behind Monday's record-setting rainfall in Toronto are still lingering over Southern Ontario, with a major weather event possible tonight or tomorrow, according to CBC meteorologist Ross Hull.
The humid, unstable air mass that was in place Monday is still in effect today, said Hull, meaning the potential for thunderstorms is still there.
As of 4:35 ET, Environment Canada said thunderstorms and a risk of torrential downpours remain a possibility this evening and overnight for parts southern Ontario, including Toronto.
Last night, 126 millimetres of rain fell in Toronto, the most the city has seen in a 24-hour period since Hurricane Hazel in 1954, and more rain than the city normally sees in a month.
On Wednesday, a fast moving cold front tracking across the U.S. Midwest is poised to bring heavy rain, high winds and hail to southern Ontario with a "bullet of more severe weather" aimed at Thunder Bay.
"Carry an umbrella and watch those skies closely," Hull said.
Why was the storm such a surprise?
A cool breeze flowing off Lake Ontario onto land helped lift and slow the storm as it moved over downtown Toronto, said Hull.
The storm's potency and resulting flash flooding can be blamed on the unusual amount of moisture held in the atmosphere.
"We often see heavy downpours with summer storms," said Hull, but weeks of humidity combined with that lake breeze meant Toronto was "primed for storms."
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The record breaking storm turned Toronto streets and subway stations into lakes, leaving thousands of residents without power.