Localized flooding is possible.
Ontario's weather forecast says a cluster of isolated thunderstorms will arrive Thursday afternoon and it's about to get intense.
A severe thunderstorm watch has been put in place for multiple locations across Ontario, including Toronto, Peel Region and London, and is warning of "dangerous" conditions.
According to Environment Canada, localized flooding, hail, dangerous winds and torrential rain are some of the conditions the thunderstorms could produce.
Heavy downpours of up to 50 millimetres could accumulate within short periods of time, with some storms producing 90 km/h winds.
"Heavy downpours can cause flash floods and water pooling on roads. Lightning kills and injures Canadians every year. Remember, when thunder roars, go indoors," the government department says.