Severe thunderstorms cause major flooding and power outages in eastern Ontario and southern Quebec, Canada

Severe thunderstorms swept through eastern Ontario and southern Quebec on Sunday, July 13, producing up to 100 mm (3.9 inches) of rain within 90 minutes, widespread flash floods, damaging winds, and extensive power outages affecting tens of thousands of customers.

The storm system developed as a fast-moving cold front, traveling at approximately 40 km/h (25 mph), interacted with a hot and humid air mass in the region, triggering multiple intense thunderstorm cells.

Environment and Climate Change Canada issued severe thunderstorm warnings across southern Quebec and eastern Ontario early in the day, warning of wind gusts up to 90 km/h (56 mph), nickel-sized hail, and the possibility of flash flooding and power disruptions.

The most severe impacts were observed in the greater Montreal region during the early afternoon hours.

Montreal-Trudeau International Airport recorded 58 mm (2.3 inches) of rainfall in just one hour, while some neighborhoods registered up to 100 mm (3.9 inches) within a 90-minute period. This marked one of the wettest July days on record for the city.

Total rainfall across Montreal ranged between 70–100 mm (2.8–3.9 inches). On the North Shore, precipitation totals reached between 80–110 mm (3.1–4.3 inches), while the South Shore recorded between 40–70 mm (1.6–2.8 inches).

Flash flooding affected residential districts, including St‑Leonard, where streets and basements were inundated. Major roadways such as Highways 40, 15, and 25 were submerged and temporarily closed due to rising water levels. Wind gusts reached 60 km/h (37 mph) at Ottawa Airport, with scattered reports of localized infrastructure damage across both urban and rural areas.

Hydro‑Québec reported more than 60 000 customers without power at the peak of the storm. As of 16:15 LT, outages had been reduced to around 33 000 addresses, but by early evening the number had climbed to 36 726 as new outages occurred. The most affected areas included Montreal with over 13 000 customers in the dark, Montérégie and Lanaudière with over 5 000 each, and 4 600 outages in the Laurentians. In eastern Ontario, utilities reported a few thousand outages, though most were resolved by the following morning.

Operations at Montreal-Trudeau International Airport were disrupted by the storm, including delays in flight schedules, baggage handling, and ground services due to lightning and rainfall conditions. Passengers were advised to check flight status with their carriers.

The Festival d’été de Québec adjusted its final night programming due to the storms. Although start times were delayed, performances resumed once conditions stabilized.

The thunderstorms occurred during a regional heat event. A heat warning remained in effect for much of Ontario and Quebec, with temperatures exceeding 30 °C (86 °F) and humidex values approaching 40 °C (104 °F). These conditions persisted into the following day, complicating cleanup and recovery operations.

References:

¹ Thunderstorm knocks out power, disrupts flights in Montreal – City News – July 13, 2025

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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