Cornwall, Ontario is under a heat alert this week as Environment Canada warns of a prolonged stretch of hot, humid weather that could feel like 40°C. The Environment Canada MetNote alert began Monday, June 29, 2026 and is expected to last through Saturday, July 4. It urges residents to check on family, friends and neighbours, especially those who live alone, to make sure they have a cool space.
The hottest days are forecast for Wednesday, July 1 and Thursday, July 2, with highs reaching 33°C and humidex values between 38 and 40. Eastern Ontario Health Unit officials note that heat warnings kick in when daytime highs hit at least 31°C, overnight lows stay at or above 20°C, and the humidex is forecast at 40 or more for two days straight.
Health Canada says most heat-related deaths in the country happen indoors, putting older adults, young children, people with chronic illnesses and those who cannot keep their homes cool at greatest risk. New Ontario rules taking effect Wednesday, July 1, 2026 also make it easier for tenants to install air conditioners, as landlords can no longer refuse if the tenant provides written notice and meets certain conditions.
The heat wave lines up with what Environment Canada says will likely be one of the four hottest years on record worldwide. Canada is warming more than twice as fast as the global average. Last summer, Toronto emergency rooms fielded 74 heat-related visits across six heat waves.
The alert runs through the Canada Day long weekend, and health officials remind Cornwall residents to drink plenty of water, seek shade or air conditioning, and never leave children or pets in parked vehicles. Anyone needing a break from the heat can contact the Eastern Ontario Health Unit or the City of Cornwall for information on cooling centre locations.
