Devastating flash flooding on the West Island

Heavy rain from strong thunderstorms quickly overwhelmed the sewer system, inundating roads across parts of the West Island on Saturday afternoon. (West Island Community Page via Facebook)

Powerful moisture-latent thunderstorms swept across parts of the West Island and South Shore on Saturday afternoon, producing nearly two month's worth of rainfall in just a few hours. The slow moving thunderstorms impacted a relatively small area of the Island of Montreal, focusing on Pierrefonds-Roxboro, Pointe-Claire and Dollard-Des Ormeaux. In those communities as much as 170mm of rain fell between 3 pm and 7 pm.

Heavy rain also fell in Dorval, with 60mm at Trudeau Airport. In stark contrast, I only measured 5mm at my weather station here on Ile Perrot.

The result of the torrential rain was immediate, with several main roads, including Highway 40 between Sources and Saint John's Boulevard becoming inundated with water and impassable. Drivers became trapped in their cars by rising flood waters, with at least 15 requiring rescue by Montreal Firefighters. Montreal Division Fire Chief, Martin Guilbault, said his department responded to nearly 800 calls within the first hour of flooding and close to 1200 overall.

At least a dozen communities have been impacted by devastating flooding, affecting hundreds of homes and vehicles.

The Montreal Fire Department responded to over 800 calls in  first hour after the flooding began. Above the department arrives to rescue drivers trapped in their vehicles on Gouin Boulevard in Pierrefonds. (Photo Peter Turnbal)

Nearly four hours of lightning at Trudeau Airport, resulted in a ground stop for safety reasons. Dozens of flights were canceled or delayed and at least 25 incoming flights were diverted to other airports. Between 3 pm and 7 pm it was a constant rumble of thunder to my east over the West Island as dark clouds moved from northwest to southeast and onto the South Shore.

Hail and strong wind gusts also occurred with the storms. As a result of the flooding, Hydro-Quebec needed to cut power to most of the affected area. That combined with other storm effects, such as wind and lightning, resulted in the loss of power to over 25,000 customers. Most of the power was restored early Sunday according to  media relations spokesperson Paule Veilleux-Turcotte.

At least 300 homes were severely damaged by flood waters, but that number is likely much higher. The clean up began in earnest on Sunday, but was interrupted by more weather warnings and thunderstorms. Sunday's storms were a little more tame, as the Atlantic Canada system began to weaken. They still managed to dump heavy rain over the area, with 16.2mm on Ile Perrot in just 30 minutes. That storm also produced hail and strong wind gusts.

As Saturday's storms moved onto the South Shore, more significant flooding and road closures occurred in Saint-Constant, La Prairie, Chateauguay and even as far south as Napierreville.

The thunderstorms were the result of deep moisture pinwheeling around low pressure located over Atlantic Canada. It was the same storm the brought heavy rain and severe weather to Ontario and Quebec last Thursday.