The hot spell coming in from the U.S. has pushed the mercury from southwestern Ontario through to Quebec City to the low 30s, but it feels more like 40 degrees or more due to soaring humidex values, Environment Canada said. Cooler air is forecast to drop temperatures down into the 20s starting Friday.
Smog advisories are in effect from Windsor to Kingston, and special heat alerts or heat warnings have been issued in several municipalities across the region, including Toronto, where cooling centres have been opened for people vulnerable to hot temperatures.
Children, seniors and those with disabilities and chronic illnesses are most at risk during hot weather like this, said Paul Buttery, environmental health specialist for Lambton County in southwestern Ontario.
Lambton County and the City of Sarnia have eight designated areas for people to take refuge from the heat, though Buttery said so far he hasn't heard of a jump in the number of people seeking emergency help for heat exhaustion, which can occur after several days of exposure to hot weather.
If you're coming down with heat exhaustion, Buttery said, then "the best thing to do is stop all activity and seek a cool place, drink water and seek medical attention immediately if your symptoms worsen."
The danger is heightened in areas under a smog alert.
Breathing smog can have a big impact on lung health and lead to inflammation and swelling, but those at the greatest risk may not realize it until they break a sweat doing outdoor activities, cautioned Ted Boadway, a smog expert with the Ontario Medical Association.
"If they're (doing) no exercise they won't notice much difference, but if you try to exercise you'll notice a great deal if you've lost a lot of lung function."
Those with respiratory illnesses like asthma and chronic lung disease are "sitting ducks" during humid, smoggy weather, he said, adding it also hits those with cardiovascular problems, ratcheting up the risk of strokes and heart attacks.
Experts advise the best way to avoid the risk of heat-related illness is to stay indoors and crank up the air conditioning.
Heat-related electricity demand isn't overloading the Ontario power system, provincial Energy Minister Chris Bentley said.
"We've brought on enough energy generating capacity precisely for peaks like today. We do have enough."
The Independent Electricity System Operator, which monitors electricity demand in Ontario, said energy use Wednesday isn't expecting to crack the top 20 peak-demand days.
But people can still enjoy the outdoors during hot, smoggy days as long as they know how to stickhandle around smog-related risks, said Boadway, who now takes his afternoon walk in the morning before hot weather arrives in force.
"The important thing to remember is: I've got (a life) to live, I still have to do things, just try to do it smarter."
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