Heat warning blankets southern Ontario as temperatures soar into high 30s

An Environment Canada map shows an Orange Heat Warning in effect for much of southern Ontario. June 30, 2026. (Source: Environment Canada)

An orange heat warning, cautioning of a long-duration heat event, continues for much of southern Ontario.

The warning stretches from Windsor-Essex, through Sarnia and Lambton County, London, Middlesex, Perth, Huron and all the way through the GTA, up to Peterborough.

Environment Canada says maximum temperatures of 31 to 34 degrees C, and potentially up to 37 C are possible for some areas, with minimum temperatures of 21 to 25 C.

The warning is expected to continue through Friday and possibly into the weekend with the hottest days expected through Thursday, with maximum temperatures of 34 to 37 C. The agency said minimum temperatures of 21 to 25 C will provide little relief from the heat.

Hot and humid air can also bring deteriorating air quality and can result in the Air Quality Health Index approaching the high-risk category.

Residents are reminded to take action to protect themselves and others, and to check on older adults, those living alone and other at-risk people in-person or on the phone multiple times a day.

Speaking with CTV News, Dr. Anna Gunz of London Health Sciences Centre says people may not even realize they’re suffering from heat-related effects when it happens.

“Heat affects our whole body. Our mental health, and our physical health. So, the most important thing is to stay cool. And I think what people don’t realize, while it might be intuitive to get heat stress or heat stroke in the moment, it also sets us up, it puts a lot of strain on our body for other illnesses as well,” Gunz explained.

Middlesex-London Health Unit safety recommendations

• Drink plenty of water and natural juices throughout the day, even if you don’t feel very thirsty.
• Never leave a child or pet in a parked car or sleeping outside in direct sunlight.
• Avoid drinking caffeinated or alcoholic beverages, including coffee and cola.
• When possible, avoid spending too much time outdoors. If you must be outside, seek shade as much as possible and plan outdoor activities in the early morning or evening.
• Wear a wide-brimmed hat when outdoors.
• Keep shades or drapes drawn and blinds closed on the sunny side of your home.
• Avoid turning on electric lights in your home.
• Take a cool bath or shower periodically or cool down with cool, wet towels.
• Avoid intense or moderately intense physical activity.
• Use fans to draw cool air at night, but do not rely on a fan as a primary cooling device during extended periods of excessive heat.
• Reduce the use of personal vehicles and unnecessary idling.
• Avoid using oil-based paints and glues, pesticides, and gas-powered small engines.

Here’s a look at the extended forecast

Tuesday: A mix of sun and cloud. Wind southwest 20 km/h gusting to 40. High 33. Humidex 43. UV index 10 or very high.

Tuesday Night: Clearing this evening. Wind southwest 20 km/h gusting to 40 becoming light near midnight. Low 22.

Wednesday: A mix of sun and cloud. 40 per cent chance of showers in the afternoon with risk of a thunderstorm. Wind becoming southwest 20 km/h gusting to 40 near noon. High 34. Humidex 44. UV index 9 or very high.

Thursday: Sunny. High 34.

Friday: A mix of sun and cloud with 40 per cent chance of showers. High 33.

Saturday: A mix of sun and cloud. High 31.

Sunday: A mix of sun and cloud with 30 per cent chance of showers. High 28.