THE CANADIAN PRESS -- TORONTO - TORONTO - A night thick with muggy heat, clammy skin and sweaty sheets broke records in southern Ontario early Thursday and was followed by a day of blazing hot sunshine and searing temperatures.

The humidity dropped slightly after the soupy night, but soaring temperatures kept shirts clinging to lower backs as people began their morning commute under humidex values pushing 40 C.

Environment Canada forecast highs of 34 C for Montreal and Ottawa, though it climbed to about 36 C in the nation's capital. A high of 38 C was predicted for Toronto and 39 C for Windsor, Ont. By mid-afternoon the southern Ontario border city felt like 50 C with the humidity.

To put it in perspective, most steam rooms are set at temperatures between 37 and 40 C.

"I'm standing in the shade just so that I don't get fried like eggs," said 24-year-old Chris Parkinson outside of Toronto's Eaton Centre.

Weather watchers were keeping a keen eye on the mercury as it climbed close to previous records. In Toronto the record downtown is 40.2 C, which was set during a heat wave in 1936. The record at Pearson International Airport is 38.3 C, which was set in 1948. It was likely higher there during the 1936 heat wave, but record-keeping didn't start at the airport until 1937.

In Windsor, records date back to 1940 and the hottest temperature on file is 40.2 C, which was set on June 25, 1988.

But what catches the eye of Canada's most famous climatologist more than the scorching daily highs are the nights that provide no relief.

Several places in southern Ontario recorded their hottest nights ever. In Toronto, for example, the coolest it got overnight was 26.6 C, which was at 5 a.m., and by 6 a.m. it was already up to 27.1 C. The previous record for the hottest night came on Aug. 1, 2006, when the lowest overnight temperature was 26.3 C.

Several other Ontario cities, such as London and Hamilton, also saw their hottest nights ever, said Environment Canada senior climatologist Dave Phillips.

"Back in the famous heat waves of the past you could always count on the nights cooling off so the body could build back," he said.

"What's becoming more characteristic of our kind of heat waves now is not so much the excruciating high temperatures, it's the elevated minimum temperatures."

A telling factor is the dew point, Phillips said, which is a measure of humidity. Around 6 a.m. the dew point in some parts of Ontario was about 23 when the temperature was about 27.

"The difference between the air temperature and the dew point tells you how clammy it is, how close it is, why you have wet sheets," he said.

"It shows you why you're dripping wet. It's like being in a fog or in a cloud as you're walking around. Not only is it hot but the air, you could cut it with a knife."

Toronto's Giovanni Mcleish, 20, likened the suffocating heat to being ''hit with a speeding train."

"It's a wall of heat," he said in downtown Toronto. "It feels like I can't breathe."

While many people took refuge in air conditioned spaces like shopping malls or splashed around in public pools, some were enjoying the sweltering temperatures.

"It's a lot better than the snow," said 42-year-old Robert McKenzie of Toronto as he enjoyed his lunch break in the shade. "Leave it on."
Environment Canada issued a warning Thursday about extreme temperatures and humidex values for all of southern Ontario as the mercury is expected to soar into the mid- and even high-30s. There was also a high heat and humidity warning for parts of northern Ontario and southern Quebec.

A hot, unmoving high-pressure area created a heat dome effect over central parts of Canada, pushing the jet stream well to the north, and keeping cooler or wetter weather away.

Meanwhile, the Toronto Blue Jays played under another kind of dome after deciding it was too hot to open the retractable roof at Rogers Centre for Thursday's matinee against the Seattle Mariners.

Thoroughbred racing at Toronto's Woodbine Racetrack was cancelled Thursday afternoon due to concern for the horses.

Canada Post mail carriers in heat dome regions were allowed to start their routes in the early-morning hours, so they weren't out during the hottest part of the day.

Spokesman John Caines said Canada Post also offered mail carriers sunscreen, hats and water.

"They're professionals as well, so they know how to conduct themselves in this kind of weather, but if they can get out early and get the mail before it gets too, too hot and get it all delivered, then it's better for everybody," he said.

Many construction workers were also hoping for an early day.

"I'm tired and it's stuffy," said 25-year-old Ronan Shannon of Toronto. "We just want to go drink beer."

Shannon and his co-worker Brett Lindsay, 22, said staying shirtless and drinking fluids was their strategy to get through the day.
Despite the soaring temperatures, the province's power supply was expected to meet demands.

The Independent Electricity System Operator predicted peak demand wouldn't crack 26,000 megawatts. The all-time high was Aug. 1, 2006, when Ontario needed 27,005 megawatts of electricity.

IESO spokesman Terry Young said lower industrial demand is one of the reasons no power records will be broken.

Toronto Emergency Medical Services recommended people drink lots of water, stay out of the sun, especially between 11 a.m. and 4 p.m., check on elderly or ill neighbours and visit a cool location for those who don't have air conditioning at home.

Troubling signs to watch for in the heat include dizziness, nausea, headaches, lethargy, muscle cramping, shortness of breath, chest pain and fainting.

— With files from Alexandra Posadzki