Millions in Ontario will see temperatures near 37 C Tuesday as the “peak” of a heat wave over the province settles in, Environment Canada says.
The federal weather agency has placed southern and eastern Ontario under a yellow heat warning, while a large portion of northern Ontario is under an orange heat warning.
“Today will mark the peak of this heat event. Maximum temperatures near 37 degrees Celsius are expected this afternoon for some areas over southwestern Ontario, around the Greater Golden Horseshoe and eastern Ontario,” its warning reads.
Humidex values will make it feel like 38 to 45 degrees. Lows of 20 to 25 degrees are expected.
Get breaking National news
Get breaking Canada news delivered to your inbox as it happens so you won’t miss a trending story.
“Hot and humid air can also bring deteriorating air quality and can result in the Air Quality Health Index approaching the high-risk category,” Environment Canada said.
“Take action to protect yourself and others – extreme heat can affect everyone’s health. Determine if you or others around you are at greater risk of heat illness. Check on older adults, those living alone and other at-risk people in-person or on the phone multiple times a day.”
The federal weather agency also detailed the early signs of heat exhaustion, which may include headache, nausea, dizziness, thirst, dark urine and intense fatigue. Symptoms of heat stroke can include red and hot skin, dizziness, nausea, confusion and change in consciousness.
It added to drink water often and before you feel thirsty to replace fluids, and to close blinds or shades and open windows if outside is cooler than inside, as well as turn on air conditioning, use a fan or move to a cooler area of your living space.
Several municipalities, including Toronto and Hamilton, have opened cooling stations and pools for residents to keep out of the heat.
The heat event is expected to end Tuesday night for regions in central and northeastern Ontario, but will persist into Wednesday or Thursday for southern Ontario.
© 2026 Global News, a division of Corus Entertainment Inc.