Environment Canada has issued a heat advisory ahead of hot Sunday and Monday forecasts.
Waterloo Region and Northern and Southern Wellington Counties are expected to be the affected areas.
Humidex values near 40 C are possible, the Environment Canada website said, without much chance for relief at night.
A cold front Monday is expected to offer relief from the heat.
While extreme heat affects everyone, the most susceptible are children, pregnant women, older adults and people working outdoors or with chronic illnesses.
