Strong thunderstorms cause flooding & damage in Montreal

Just one of several roads that were closed across the Montreal region on Thursday afternoon as a result of several rounds of strong thunderstorms. (CBC)

A series of strong thunderstorms swept across southern Quebec on Thursday afternoon as a cold front sliced into a warm, muggy and highly volatile air mass. The result was cell after cell of powerful thunderstorms, some of which generated isolated tornadoes. In Montreal, the storms arrived around 4pm, moving southeast across the city through 7pm. The airport reported thunder and lightning for four consecutive hours, an extremely rare even for Montreal.

A lightning strike ignited a fire that destroyed two homes and damaged a third in Saint-Marthe-sur-le-Lac northwest of Montreal. (CTV)

The end result was 40 to 60mm of rain in a short period of time, creating flooding on several highways and a nightmare commute home for many. Several underpasses were closed after vehicles became disabled in rising flood water. The storm produced large hail in swath from Hawkesbury, Ontario into Lachute and Two Mountains north of Montreal. Smaller hail of less than 2cm in diameter was reported within the city.

A lightning strike just after 4pm ignited a fire that destroyed two homes and damaged a third in the off-island north shore community of Saint-Marthe-sur-le-Lac. It took firefighters from 5 municipalities to bring the blaze under control by 9pm. No injuries were reported. Hydro-Québec reported outages to almost 43,000 customers during the evening hours, but that number it down to just over 6700 Friday morning.

Day turned to night a severe thunderstorms crossed the Ottawa River to begin their assault on the Island of Montreal just after 4pm on Thursday. (ValleyWeather Photo)

Several regions of Quebec were under tornado watches and warnings Thursday afternoon, but no official reports are in as of my writing.  I did observe plenty of rotating clouds from my vantage point on Ile Perrot. I measured 30mm of rainfall, the bulk falling between 5-6:30pm. Trudeau Airport measured 39.6mm of rain, with 62mm at St Hubert Airport on the south shore.

The severe weather also impacted parts of eastern Ontario, with major damage reported in Bellville, Ontario where winds gusted to 106km/h. Several roofs were damaged along with downed trees and power lines. Western University's Northern Tornadoes Project will be investigating the damage today to determine if tornadoes occurred during the storm.

In the wake of the storms, Friday will be partly cloudy with scattered showers and isolated thunderstorms this afternoon. The strongest of the storms today be southeast of Montreal. The high will be 25C (77F). Behind a secondary cold front today, much cooler air will pour into the region. Saturday will be cloudy, with showers and unseasonably cool, with a high of only 14C (56F) forecast.

The good news is that Sunday will be sunny with near-perfect weather for the Canadian Grand Prix. Expect dry conditions and a high of 21C (70F).