A sizzling heat wave broke 16 records in communities across Canada Wednesday, despite cooler temperatures in Alberta and Saskatchewan.

Markham, Ont., was the day's hotspot at 35.9 C, breaking the record of 35.6 set back in 1991.

Eight Quebec towns broke their own high temperature records, along with six in Ontario and two in Manitoba. The regions saw temperatures in the low to mid-30s, with increasing humidity meaning humidex values in the low 40s.

Saskatchewan and Alberta temperatures, meanwhile, dipped in many areas, likely a welcome relief to some.

The heat and humidity have triggered heat alerts, brought thunderstorms and helped spark forest fires.

And there's no sign of relief yet for central Canada.

In Ontario, Toronto is forecast to hit 38 C with a humidex of 48 Thursday. The highest temperature ever recorded at Pearson airport was 38.3 C on Aug 25, 1948. Moving to downtown Toronto, the highest ever recorded temperature was 40.6 C on July 8, 1936.

Windsor, Ont., could hit 49 with the humidex.

Most of southern Quebec is under a smog advisory through Thursday. An advisory for Windsor-Essex-Chatham Kent, Ont., lifted Wednesday night.

Caitlin Graham, 14, uses a waterslide to beat the heat at a public pool in Winnipeg on Tuesday. (John Woods/Canadian Press)

But this isn't the hottest weather Canada has ever seen, said CBC meteorologist Nick Czernkovich.

"Some of the records that go back into the 1930s [show] much more in the way of heat," he said. "[On] July 5, 1937, Saskatchewan saw temperatures into the mid-40s, actually at 45 degrees," he said.

"The deadliest heat wave came in July of 1936 when temperatures exceeded 44 degrees in Manitoba and Ontario, and 1,180 deaths were attributed to that particular heat wave."

Thursday has the potential to be the hottest day ever recorded in Toronto, with Environment Canada calling for a high of 37 C. The highest temperature recorded in the city was 38.3 C on Aug. 25, 1948, at the airport.

Toronto's medical officer of health has declared an extreme heat alert for the city until further notice and smog alerts have been issued for the Windsor, Essex, Chatham and Kent areas.

The heat wave will continue through Friday and into the weekend for most of southern and eastern Ontario. Ottawa's chief medical officer has issued a heat warning for Wednesday and Thursday.

The Independent Electricity System Operator in Ontario expects record demand for energy Thursday, but says the system is ready for it.

In northern Ontario, dozens of wildfires triggered by lightning and tinder-dry conditions continue to burn.

In Manitoba, Winnipeg hit a record-tying 34 C with a humidex of 43 Tuesday, but was expecting a slightly lower high of 29 C Wednesday.

Relief for Alberta and Saskatchewan

Meanwhile, there was some relief in the Prairies, with temperatures coming down five to 10 degrees Wednesday in parts of Alberta and Saskatchewan.

However, the system pushing eastward was also expected to bring thunderstorms and heavy rains, with up to 150 millimetres possible in some areas.

While some people decry the heat and sticky skin, lots of Canadians wonder what the big deal is. Several people in Saskatchewan told CBC News that the hot and humid weather is exactly what they'd been hoping for.

Sarah Liberman, who was enjoying lunch in Wascana Park in Regina, said she had been talking to a friend who seeks out the kind of tropical weather Canada is experiencing this week.

"So if he gets this here he's not going to complain at all," she said. "And I thought that was such a good perspective."

For those who don't like the heat, they can at least take solace in the thought that it has been even hotter in the U.S.

The oppressive conditions extend from the northern Plains states to Texas and from Nebraska to the Ohio Valley.

The daily highs in Oklahoma have been at least 38 C for 29 straight days, and Council Bluffs, Iowa, had a humidex reading Tuesday that made it feel like 52 C.

With files from The Canadian Press and The Associated Press