High winds caused by storms that swept through parts of southern Ontario and Quebec are being blamed for the death of 21-year-old woman and the loss of power to hundreds of thousands of people in both provinces.

21-year-old woman died after she was struck by a falling tree branch at pool in Boucherville, Que., on Montreal's south shore. Two other people were hurt — a 6-year-old boy and a 40-year-old woman.

By midnight, about 400,000 customers in Quebec were still without power in the wake of severe storms that passed through the province. High winds and falling tree branches are to blame for the outages, Louis Olivier Batty, a spokesperson with Hydro-Québec, said earlier Friday.

Late Friday, Hydro One said crews were still working across Ontario to restore power to over 150,000 customers.

After a slew of warnings earlier Friday, tornado warnings that were in effect across southern Ontario were downgraded to either severe thunderstorm warnings or watches.

Ottawa was briefly under a tornado warning Friday afternoon. That warning had been downgraded to a tornado watch as of 7:45 p.m. ET. 

Storm warnings and watches remained in place for a large swath of southern as a cold front sweeps into the province with storms that will lift the heat that has blanketed Ontario and Quebec over the past week. 

A watch means conditions are favourable for storms, while warnings mean extreme weather is occurring or imminent.

Strong winds and heavy rains were the primary result of a series of "massive" storm fronts moving through the region Friday afternoon. The monster storm cells — some reaching upwards of 14, 000 metres — sparked tornado warnings across southern Ontario.

Residents of Perth, the Halton Hills area, Kingston, London, Peterborough, Kingston, Sarnia, Kitchener-Waterloo and Hamilton were at times under the threat of a tornado.

People in the northern Ontario communities of North Bay, Powassan, Mattawa area and West Nipissing-French River were briefly under a tornado warning Friday morning.

Montreal was also touched by a tornado warning today. Friday afternoon, the temperature in Montreal hit a high of 33 C, feeling like 45 with humidex.

With the latest batch of storms sweeping across central Canada Friday, it would seem the heat and humidity characteristic of the past week has dissipated.

A "potent" cold front moving across the country from the northwest mixed with the heat and humidity sitting over central Canada meant "this was always going to be a stormy day," said CBC meteorologist Claire Martin. 

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Storm clouds roll over downtown Toronto Friday evening. Environment Canada issued a severe thunderstorm warning for much of southern Ontario, including Toronto on July 19. (Evan Mitsui/CBC)

The cold front marks a real change in the weather this weekend for Ontarians, who can expect much cooler, fresher air to settle in, Martin said. 

On Friday, the Toronto area hit day four of a heat wave — considered to be three straight days of 32 C or higher — when a high of 33.2 C was measured at Pearson International Airport. Ottawa reached the same status by Wednesday.

In Mississauga, hundreds of residents of an apartment building were forced outside in the sweltering conditions early Friday after an electrical fire cut power to their building.

The Maritimes will also be muggy and unsettled Friday as humid air moves in with humidex values in the low to mid 30s, and a thunderstorm risk for New Brunswick.

Eastern Canada isn't alone in facing severe weather. In Western Canada, there is a risk of thunderstorms in large swath south of a line that extends from northeastern B.C. through Saskatoon to southwestern Manitoba.



This time-lapse video, posted to YouTube on July 19, shows storm clouds rolling over the campus of Georgian College in Barrie, Ont. shortly before a tornado warning was issued for the area.