The heat continues in southern Ontario and southern Quebec Thursday, with humidex values in the high 30s and low 40s. 

Toronto recorded the city's first heat wave of the summer Thursday with temperatures at Pearson International Airport reaching 32 C or higher for the third day in a row. Environment Canada no longer issues a formal heat wave notice but, "unofficially" today's high of 33.6 C means "we've hit the mark," CBC meteorologist Claire Martin said.

The trend will continue with an "easy" high of 33 C tomorrow, but after that "we should see some relief with gradual cooling" as a cold front pushes through over the weekend, she said.

Tornado warnings lifted

Environment Canada issued tornado warnings for communities north of Toronto Thursday afternoon. By 3 p.m. ET, most had been lifted and by 4 p.m. ET, the warnings had been downgraded to thunderstorm watches.

Some severe thunderstorm watches remained in effect across parts of southwestern and eastern Ontario.

Montreal, along with much of southern Quebec, is under a high heat and humidity warning while the threat of severe thunderstorms continue to loom over the region.

The humidity fuelled strong thunderstorms from eastern Ontario to New Brunswick yesterday, leaving as many as 60,000 customers without power in Montreal. About 9,400 Hydro-Quebec customers were still without power as of 10 a.m. Thursday.

Quebec health officials said on Wednesday that they are investigating two deaths that may be connected to the heat.

Officials urged anyone caught in the heat to drink lots of water and, if possible, seek relief in a local cooling centre, or an air-conditioned spot such as a movie theatre.

Hot weather has also affected the U.S. this week, with the country's largest heat wave of the summer stagnating over large regions, bringing sizzling temperatures from South Dakota to Massachusetts.

New York State's power grid operator forecast that peak electricity usage Thursday would break a record set in 2006, as consumers crank up their air conditioners. 

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Environment Canada issued tornado warnings for communities north of Toronto Thursday afternoon. By 3 p.m. ET, most had been lifted but as of 1:30, some 2 million people were told to take cover under warnings that stretched from Mississauga acorss southern Ontario to Vaughan. (Environment Canada)

With files from The Associated Press and Reuters