Officials are warning people planning outdoor activities to be mindful of the heat warning and air quality.
Environment Canada has also issued a heat warning and air quality statement for the London region.
Hot and sunny conditions are expected to cause increasing ground-level ozone concentrations making breathing difficult for some.
Temperatures were expected to reach the low thirties Sunday and Monday with peak humidex values near 40.
The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors.
A cold front will cross Southern Ontario tonight ending the heat event.
