Thousands of people across Ontario and Quebec are without power after severe thunderstorms on Canada Day brought down trees and flooded homes in some regions during a stubborn heat wave that is now spreading further east.

Environment Canada has scores of heat warnings posted for most of Ontario and Quebec, and now stretching across to New Brunswick, Nova Scotia and Prince Edward Island.

Much of Ontario is under an orange warning, an alert the agency says is uncommon and signals severe weather that is likely to cause significant damage or health effects.

Daytime temperatures in Ontario — from Windsor to Ottawa and Thunder Bay through Timmins and southern James Bay — have been in the mid-30s, with the humidex making it feel even hotter.

Severe thunderstorms and high winds on Wednesday caused widespread power outages in Ontario and Quebec, including in the National Capital Region where several Canada Day celebrations, including the planned fireworks show, were cancelled.

Hydro One’s outage map showed that tens of thousands of customers across Ontario still had no electricity as of Thursday afternoon, although the utility said on social media that crews were making significant progress.

The storm caused flooding across the Ottawa region, closing some roads and flooding hundreds of basements.

Environment Canada said 118 millimetres of rainfall was recorded at the Ottawa airport, shy of the record daily rainfall at the same location of 135 mm, which was set Sept. 9, 2004.

Mayor Mark Sutcliffe told a press conference that other parts of the city received even more rain than the airport, calling the storm “one of the worst flooding events in our city in the last 25 years.”

He said agents handling 311 calls have struggled to keep up with more than 1,900 service requests, and more than 5,000 customers in Ottawa were still without power as of Thursday afternoon.

The storm rolling in on the country’s birthday was a sort of blessing in disguise, the mayor said, because emergency crews and municipal staff were already deployed all around the city.

“I think it was more a case of pivoting, rather than having to call people in,” he said. “I think we were actually in a better position in many ways because it was Canada Day.”

Some areas in the west end of Ottawa reported unofficial rainfall totals of up to 175 mm, said Peter Kimbell, a warning preparedness meteorologist with Environment Canada.

Kimbell said the hot and humid conditions were ideal for storms of this type, which are difficult to forecast given their volatility and their relatively small scale compared to winter storms, for example.

“It’s big scale to us, but in the world of meteorology, it’s small,” he said.

Meanwhile, more than 5,500 Quebec addresses were without power on Thursday afternoon, down from approximately 9,000 hours earlier, according to Hydro-Quebec.

The severe heat was also cited among the reasons for the cancellation of Thursday’s World Cup match broadcasts at Toronto’s Nathan Phillips Square. The city is hosting its final match at Toronto Stadium as Portugal faces off against Croatia in the round of 32.

This report by The Canadian Press was first published July 2, 2026.