An intense and prolonged heat wave, accompanied by a risk of severe thunderstorms and tornadoes, is threatening much of Ontario and Quebec starting Tuesday, June 30, 2026.
Environment Canada has issued orange and yellow weather warnings as atmospheric instability spikes, driven by daytime highs approaching or surpassing 30°C.
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The dangerous combination of heat and humidity could persist through Friday and potentially stretch into the weekend, the weather agency noted.
Metropolitan areas face extreme conditions, with Toronto and Ottawa expecting maximum temperatures of 33°C alongside a humidex reaching 42°C.
Regional temperatures will hover between highs of 35°C and lows of 23°C for the remainder of the week before a slight relief arrives next week, according to Environment Canada.
The extreme heat expands deep into northern Ontario from Thunder Bay to Timmins, where temperatures are forecast to hit 32°C with a humidex near 40°C.
Southern and eastern Quebec, including Montreal, will experience daytime highs around 33°C from Wednesday until Saturday.
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In addition to the stifling heat, severe weather systems are developing rapidly across both provinces.
Overnight thunderstorms forming a mesoscale convective system are projected to track east into northeastern Ontario early Tuesday morning, threatening the region with heavy downpours, large hail, and wind gusts up to 110 km/h, as reported by The Weather Network.
Forecasters warned that embedded rotation within these storms could produce an isolated tornado or two, particularly across eastern Ontario and Quebec.
A separate cluster of storms is expected to impact cottage country and areas east of the Greater Toronto Area before the severe environmental conditions peak over Cornwall, Ottawa-Gatineau, and Montreal by late Tuesday afternoon.
The hazardous weather outlook extends into the Canada Day holiday on Wednesday, keeping thunderstorm threats active for outdoor celebrations.
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Environment Canada advised residents to limit direct exposure to the sun, check on high-risk family members, and maintain an active emergency plan to take cover if severe weather strikes.
