Damaging, tornadic storms threaten parts of Ontario and Quebec Tuesday

A strong line of storms may travel across Ontario on Tuesday, with severe impacts moving east into southern Quebec. Large hail, heavy downpours, strong winds and a tornado or two can't be ruled out

The heat is on in southern Ontario and Quebec this week, as are the chances for severe weather.

With daytime highs approaching or surpassing the 30-degree mark, the heat will help to fuel a risk of thunderstorms in Ontario and Quebec on Tuesday. A risk of a tornado or two cannot be ruled out on Tuesday, as well.

DON’T MISS: Why extreme heat is one of the world’s deadliest weather disasters

Many folks have outdoor plans for Canada Day, which will also feature a threat of thunderstorms in both provinces. Residents should remain weather-aware Tuesday and into Wednesday, and have a plan to take cover if/when severe weather strikes.

Ontario atmospheric moisture Tuesday

Tuesday carries a tornadic risk in parts of Ontario and Quebec

The building heat in Ontario and Quebec is expected to create an increasingly unstable atmosphere, which will provide plenty of fuel for thunderstorms.

Ontario and Quebec Tuesday severe storm risk - June 30, 2026

SEE ALSO: Ontario's first extreme heat event of the summer will invade this week

In the early afternoon on Tuesday, the storms will track into the Ottawa Valley from cottage country, where we could see some turn severe around the Bancroft-Montreal corridor.

By the late afternoon, a severe environment peaks over eastern Ontario and southern Quebec, including Cornwall, Ottawa-Gatineau and Montreal. The main threats forecasters are keeping a close eye on are damaging winds up to 110 km/h, large hail, and a tornado or two.

Content continues below
Ontario and Quebec Tuesday night forecast thunderstorms model 1 - June 30, 2026

There is, however, some model disagreement about the exact timing and location of the storms throughout the day.

Tuesday night, a new cluster of storms develop near Sault Ste. Marie, and may track into southern Ontario by early morning Wednesday.

We may also see another storm cluster bubble up near Ottawa-Gatineau, as well as along Highway 417 into the Montreal area later in the evening and overnight.

Ontario and Quebec Tuesday night forecast thunderstorms model 2 - June 30, 2026

Heat safety is vital

Extreme heat claims more lives around the world than any other type of severe weather.

Everyone is susceptible to heat-related illnesses without taking proper precautions, such as frequent breaks, adequate hydration, and air conditioning.

Symptoms of heat stroke and exhaustion

The compounding stress of hot days followed by muggy nights can be especially hard on vulnerable populations like the elderly, those with chronic health conditions, and folks who live without access to air conditioning. Keep in mind that certain medications can lower your body’s heat tolerance.

WATCH: How to keep your cool as a parent this summer

Thumbnail courtesy of Adrienne Miller, taken in Kingston, Ont.