Canadians were sweltering under a heat wave across much of the country on Tuesday as Environment Canada issued extreme heat warnings for multiple provinces.
Heat warnings now cover most of Ontario along with parts of Quebec, Manitoba and the Northwest Territories, meaning millions of Canadians are going to be impacted as the temperatures soar.
Environment Canada categorizes hot weather as an extreme heat event when daily temperatures reach heat warning thresholds on two or more days in a row with no relief overnight, sometimes with high humidity.
“Canadian’s need to be mindful that temperatures are reaching extreme levels and to not overdo it during the hottest times of the day,” said Global News meteorologist Anthony Farnell.
“The weather will be improving as the heat dissipates so more typical summer weather is on the horizon but I do expect to see additional heat domes before the summer is over,” he added.
Canada is facing what many experts refer to as a “heat dome,” or a high pressure system that can trap heat in a region.
“A head dome is the equivalent of putting a lid on a boiling pot of water. It traps in the heat, in this case from solar radiation, and feeds back on itself day after day until the dome breaks down,” Farnell said, adding that heat dome events are becoming more frequent.
In southwestern Ontario, including in Toronto, maximum temperatures could swing between 30 and 37 C, Environment Canada said, with humidex values ranging from 38 to 40.
Tuesday marked “the peak of this heat event,” the alert said.
“Maximum temperatures near 37 degrees Celsius are expected this afternoon for some areas over southwestern Ontario, around the Greater Golden Horseshoe and eastern Ontario,” Environment Canada said in its alert.
Parts of Quebec could see daytime temperatures close to 30 C, while northern Manitoba could see temperatures reaching 29 C.
“A heat event continues Monday through to Wednesday for parts of northern Manitoba,” the alert said.
A “significant heat wave” is underway in much of the Great Lakes area and is expected to last for most of mid-July, the U.S. National Weather Service said.
“Even for mid-July, the heat is expected to be exceptionally rare for some locations and produce numerous daily temperature records, while potentially nearing monthly and all-time records,” the NWS said in a weather alert on Monday.
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Environment Canada is asking Canadians to watch for early signs of heat exhaustion in themselves and others around them.
Older adults, young children and infants, those with chronic illnesses and those who work outdoors during the daytime are the most vulnerable to heat-related illness, Health Canada says.
Health Canada recommends wearing loose-fitting, light-coloured clothing made of breathable fabric, staying hydrated and avoiding outdoor activities during peak heat hours.
The agency lists the following as potential symptoms of heat exhaustion:
- High body temperature
- Confusion and lack of coordination
- Skin rash
- Muscle cramps
- Dizziness or fainting
- Nausea or vomiting
- Heavy sweating
- Headache
- Rapid breathing and heartbeat
- Extreme thirst
- Dark urine and decreased urination
“If you experience any of these symptoms during extreme heat, immediately move to a cool place and drink water,” Health Canada said in an advisory.
© 2026 Global News, a division of Corus Entertainment Inc.
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