Heat warning blankets most of Ontario, with humidex nearing mid-40s in Caledon this week

Hot, humid weather returns after brief break

Heat warnings cover the majority of Ontario, including Caledon and the rest of the Greater Toronto Area, as hot and humid conditions return to the province after a short reprieve.

According to Environment Canada, temperatures will peak around 37 C in parts of southern and eastern Ontario on Tuesday, with humidex values that could reach the mid-40s. Overnight will offer little relief, with low temperatures staying above 20 C.

The federal weather agency has also issued heat warnings for southern Manitoba and parts of Saskatchewan, where an orange-level warning is in place. Temperatures there could reach 40 C, with humidex values making it feel like 45.

Take precautions outdoors, medical officer says

With the FIFA World Cup semifinals beginning Tuesday, many people are expected to attend outdoor events such as Fan Fest in Toronto, or gather on patios and in bars to watch the games.

Dr. Howard Shapiro, Toronto's associate medical officer of health, told Global News that anyone spending time outside should take precautions to avoid heat-related illness.

If you're going to be outside, wear light-colored, breathable clothing, wide-brimmed hats and be sure to protect yourself from the sun by staying in a shaded area or putting on sunscreen,

He also stressed the importance of hydration. "If you get a sunburn, that's going to impair your ability to stay cool. And also make sure you have water," Shapiro told Global News.

When a heat wave moved through Toronto between June 30 and July 4, Toronto Public Health recorded 39 emergency department visits for heat-related illness, including 15 visits in a single day.

Shapiro said heat-related illness is avoidable and urged people who spend time outdoors to pay attention to how they are feeling.

"If people are able to take precautions, then you'll avoid being one of those statistics," he said. "But it's a regular pattern."

Records fall in Manitoba

While southern Ontario swelters, the brunt of the heat wave is hitting northern Ontario, southern Manitoba and southeastern Saskatchewan.

Seven Manitoba communities set new daily high temperature records on Sunday, according to Environment Canada. The highest reading, 35.8 C, was recorded in Gretna, a small community on the United States border. Records were also set in Carberry at 34.7 C, Grand Rapids at 32.9 C and Portage La Prairie at 35.7 C.

Global News meteorologist Anthony Farnell said the humidex made it feel like 48 in Winnipeg on Sunday, the hottest it has felt since temperature records began in that city.

Farnell said the frequency and duration of these heat domes appear to be increasing, calling it a worrying trend. He said the extreme heat is the result of a mix of factors, including climate change and a particularly strong El Niño.

Parts of western Quebec are also under yellow air quality warnings, with Environment Canada citing wildfire smoke causing reduced visibility and increased health risks. Farnell said overall air quality has been somewhat better this summer because of a slower start to the wildfire season.

He cautioned, however, that extreme heat and an increasing likelihood of lightning storms could spark more fires in the weeks ahead.

Farnell said temperatures will cool down again quickly, but more of these heat domes could be on the way.

"But there's still a lot of summer left," he said. "And I think we can expect, even into August, more of these big heat domes."