Environment Canada warns of high heat and humidity for southern Quebec and Ontario

Environment Canada is warning about an extended period of hot and humid weather forecast for southern Quebec and Ontario this week.

The agency has issued yellow heat warnings for Sarnia, Windsor and several other Ontario communities at risk of extreme heat beginning today.

Some regions could see temperatures of up to 36 C as well as humidex values that could reach the 40s. 

The heat is expected to move into Montreal and other parts of Quebec on Wednesday and is forecast to last until Saturday. 

Environment Canada says extreme heat puts people at risk of exhaustion or heat stroke and poses a particular danger for vulnerable people.

The agency is asking people to check on older or at-risk people and to watch for early signs of heat exhaustion, which include headache, nausea, dizziness, thirst and intense fatigue.

This report by The Canadian Press was first published June 29, 2026.

By Morgan Lowrie | Copyright 2026, The Canadian Press. All rights reserved.