TORONTO — A heat wave over Ontario and Quebec delivered a parting punch of scorching temperatures on Tuesday, as hydro crews worked to restore power to tens of thousands of customers in areas hit by forceful thunderstorms.
Across southern Ontario and Quebec, temperatures hit the low to mid 30s. The humidity made it feel closer to the low 40s.
The heat's grip was expected to loosen by Tuesday evening or into the overnight, but daytime temperatures throughout the week were still expected to be in the high 20s with a "a fair amount of humidity," Environment Canada meteorologist Steven Flisfeder said.
Any relief was expected to be short lived with more 30-degree days in the forecast starting Friday for parts of southwestern Ontario.
"It may seem like a double slap in the face to some people, especially those who are more susceptible" to heat, said Flisfeder.
Heat warnings were in place Tuesday from Windsor through to Quebec City after days of record-breaking temperatures.
Toronto, Ottawa and Montreal were among the cities to set new June 23 daily temperature records, said Flisfeder.
"It's almost too many to list off," he said.
As the high-pressure system moved east, heat warnings were extended on Tuesday to the southern part of Nova Scotia, where they were expected to remain in place through Wednesday.
Meanwhile, severe thunderstorms rolled through areas along the edges of the heat-trapping high-pressure system. Just under 32,000 Hydro-Québec customers, mostly around Québec City, remained without power as of 4:30 p.m. on Tuesday in the aftermath of thunderstorms, down from a high of around 125,000 customers, officials said.
In parts of Ontario, More Hydro One customers lost power Tuesday, adding to those who were still waiting to have the lights turned on again after weekend storms. Hydro One reported more than 4,000 customers were without power as of 4:30 p.m., up from earlier in the day.
The extreme heat and power-disrupting thunderstorms can make for a dangerous combination, said Flisfeder.
"We tend to tell people to get inside where there's AC available. Having no power, that obviously reduces the availability of that cooling and refuge from the heat and dangerous conditions," he said.
'It certainly is a concern."
Forecasters warn extreme heat this early in the season can be particularly alarming since people are not acclimatized to the high heat and humidex values, which are well above normal.
The temperatures were about 10 degrees warmer than normal for this time of year.
"It is very unseasonably warm, and the humidity just makes it even more uncomfortable," said Flisfeder.
Studies indicate that climate change, driven by the burning of fossil fuels, is increasing the length and intensity of Canadian heat waves.
Toronto's transit agency said it had implemented a few speed reduction measures along above-ground areas of its subway lines to avoid heat-related track issues. On the streetcar network, some issues had been reported with overheard wires due to excessive heat, but disruptions were temporary, said a spokesperson with the Toronto Transit Commission.
This report by The Canadian Press was first published June 24, 2025.
Jordan Omstead, The Canadian Press
