Heat warning issued for Simcoe Muskoka, humidex values could reach 45 this week

Residents and visitors deal with the heat along the waterfront in Barrie, Ont., on Tues., June 30, 2026. (CTV News Luke Simard)

Another heatwave is officially on its way.

Environment Canada has issued a yellow heat warning for Simcoe County, Muskoka, and much of southern and central Ontario with more extreme temperatures expected this week.

How hot it will get

According to the weather agency, temperatures could reach as high as 36 degrees and lows could remain above 23 degrees. Humidex values could reach 45.

The heat event is expected to take effect from Monday until Wednesday or Thursday evening.

“Tuesday will mark the peak of this heat event,” said the weather agency in its advisory. “Hot and humid air can also bring deteriorating air quality and can result in the Air Quality Health Index approaching the high-risk category.”

Widespread warnings

The heat advisories are widespread across the entire province. The yellow warnings span from Windsor to the Quebec border and all the way up to Sault Ste. Marie. Sudbury and North Bay.

Orange heat and air quality warnings have been issued for more northern and northwestern areas of Ontario, spilling into parts of Quebec, Manitoba and Saskatchewan.

Taking action

Environment Canada is repeating its safety messaging from the previous heat event two weeks ago, especially for vulnerable populations such as seniors and children.

“Watch for the early signs of heat exhaustion in yourself and others. Signs may include headache, nausea, dizziness, thirst, dark urine and intense fatigue,” said the weather agency. “Call 911 or your emergency health provider if you, or someone around you, is showing signs of heat stroke which can include red and hot skin, dizziness, nausea, confusion and change in consciousness.”

Other actions include staying hydrated before feeling thirsty, remaining in air-conditioned environments, and planning outdoor activities during the coolest parts of the day.