Stephen Balena

Stephen Balena

Hot, humid and smokey weather expected this week in Montreal, with more thunderstorms possible. 

Heat Warning in effect for Montreal. 

Round after round of heavy thunderstorms Sunday afternoon dumped between 50-100mm (2-4 inches) of rain on the city, creating widespread flash flooding once again. This is the third time in a year that Montrealers have had to deal with rising flood waters.

Sunday’s flooding was courtesy of a warm, humid and unstable air mass that had been in place for several days. Introduce a frontal boundary from Ontario tapping into deep Gulf of Mexico moisture, and you have the ingredients for slow moving, very wet thunderstorms.

On Île Perrot, between 2 and 4pm, I measured 55mm of rain. On the West Island and at Trudeau Airport, 81.7mm fell, a record for the date, surpassing the 38.6mm that fell in 2023. Some parts of north end Montreal had as much as 110mm. The 81.7mm of rain represented the second wettest June day ever recorded in Montreal, surpassed only by the 87.6mm that fell way back in 1880.

The heavy rain overwhelmed the sewers once again in Montreal, flooding major highways, surface streets and scores of businesses and homes from Lachine to Saint-Léonard to Kirkland and everywhere in between.

Sections of Highways 13-15-20 and 40, along with ramps and several underpasses had to be closed for varying amounts of time so vehicles could be removed and flood waters cleared.

Insurance adjusters will be out again surveying the damage to homes as many basements flooded across the Island.

Over 35,000 Hydro-Québec customers lost power as lines were impacted by falling tree limbs and intense lightning strikes. The storms had far-reaching effects, from south of Montreal in the Montérégie where power poles were snapped like toothpicks along Highway 138, to Mirabel and parts of the Laurentians where flooding was reported.

The heavy rain fell on what has been a relatively dry summer so far in Montreal, with only 66mm falling at Trudeau Airport up to this past Saturday. We surpassed that in just a couple of hours on Sunday, and now sit at 107.6mm for the month of July.

The storms come close to the July 14, 1987 anniversary of the Décarie Expressway flood. That storm officially dumped only 57.4mm of rain at Trudeau Airport, but amounts as high as 100 mm were reported in less than 1 hour in other parts of the city. Major flooding resulted, claiming two lives.

MORE STORMS POSSIBLE

The weather will remain very warm and humid this week, with unfortunately another risk of strong thunderstorms by Thursday. The air will also become quite unhealthy, as smoke from the western Canadian wildfires drifts into Ontario and southern Quebec. Air Quality Alerts are in place Monday for parts of southern Ontario, including Toronto, where smoke and haze are already being observed.

High temperatures in Montreal this week will range from 29C to 34C, with lows in the low to middle 20s. Humidex readings will approach 40C once again, as it did over the weekend. Heat warnings have been posted.