Canada heatwave alert: Environment Canada issues first major heat alert of 2025 as Ontario and Quebec swelter under extreme temperatures

Environment Canada has issued its first major heat warning of the year, as a dangerous heat wave engulfs large parts of Ontario and Quebec, with temperatures and humidity levels reaching extremes not seen in years.

Southern and eastern Ontario, along with southern and western Quebec, are under heat alerts as hot and humid conditions settle over the region. In many areas, daytime highs are expected between 31°C and 36°C, but with humidity, it may feel as hot as 40°C to 50°C

In Quebec, a warm, moist air mass is expected to remain over the province until midweek, bringing overnight lows above 20°C, offering little respite, particularly in urban centers like Montreal.


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Families are seeking out splash pads and community centers, while others, like construction workers and outdoor staff, are forced to endure the scorching sun. In some areas of Quebec, thousands lost power due to weekend thunderstorms, prompting fears for those without air conditioning.

Environment Canada urges residents to stay hydrated, avoid strenuous activity during the hottest parts of the day, and check in on vulnerable people, including seniors, children, and those without access to cooling.

Canada’s summer is now arriving earlier and hotter, according to the agency’s seasonal forecast. Scientists emphasize that human-caused climate change, driven by the burning of fossil fuels, is making extreme heat more likely and more intense. June heat waves, once rare, are now becoming the norm.

“This kind of heat used to be a July or August story,” said David Phillips, senior climatologist at Environment Canada. “Now we’re getting it weeks earlier, and our bodies aren’t ready for it.”

While temporary relief may come later this week, forecasts suggest more 30°C-plus days could return before July. Officials stress that early action and community support are critical in preventing heat-related illnesses and deaths.