Warning map by Environment Canada as of Monday afternoon, July 16..
While the weather is expected to cool down later this week, Environment Canada is advising those in affected areas to take care.
Large hail can injure people or damage property, Environment Canada said in a statement.
Environment Canada has issued a heat warning for much of B.C. for Monday, including Kelowna and Penticton.
A severe thunderstorm watch is in effect for North Bay, Powassan, Mattawa and West Nipissing. Gusting winds can send objects airborne, damage buildings, knock down power lines or snap tree branches.
Environment Canada is expecting the storms will diminish and pass through by this evening, but not before ushering in some potentially unsafe weather. Remember, when thunder roars, go indoors!
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Toronto's Medical Officer of Health has also issued a heat warning for the city until further notice.
It's also recommending not to leave people or pets inside a closed vehicle for any length of time.
It says the warning is expected to be in place for the next two days, with cooler temperatures and rain expected by Wednesday.
Severe thunderstorm warnings are issued when imminent or occurring thunderstorms are likely to produce or are producing one or more of the following: large hail, damaging winds, torrential rainfall.
What's more, the forecast calls for some exceptionally hot temperatures.