Severe thunderstorm watch for several regions of southern Quebec

Several regions in southern Quebec could experience severe thunderstorms on Thursday, according to Environment and Climate Change Canada, which is also warning of a tornado risk.

By mid-evening, Hydro-Québec was reporting 20,345 power outages, mainly in Montérégie, where 9,330 addresses were without power. The utility also reported 2,357 outages in Centre-du-Québec; 1,926 in Chaudière-Appalaches; 2,025 in Estrie; 1,254 in Outaouais and 1,165 in Montreal.

The federal agency issued a weather alert Thursday morning, warning of a severe thunderstorm watch for parts of Montreal, Centre-du-Québec, Laval, Montérégie, Estrie and Chaudière-Appalaches.

“Conditions are conducive to the formation of dangerous thunderstorms that could produce very strong wind gusts, damaging hail, and torrential rain this afternoon and evening,” said Environment and Climate Change Canada.

These conditions could also lead to the formation of a large-scale thunderstorm, known as a “supercell,” said Alexandra Cournoyer, weather spokesperson for the federal agency.

“These are storms with a lot of energy, a lot of moisture, and a lot of instability. “These storms have all the necessary ingredients that could come together to form a tornado,” she explained in an interview.

The likelihood of this phenomenon occurring on a large scale remains low, Cournoyer specified.

“There is a potential for localized development (of a tornado) in certain areas, but it’s not a widespread phenomenon where the formation of several tornadoes is expected,” she mentioned. This explains why the federal agency is only currently on a severe thunderstorm watch and not a tornado watch.

The thunderstorm potential is higher in the Estrie, Montérégie, and Centre-du-Québec regions, while that in the St. Lawrence Valley is at a rather moderate stage, Cournoyer emphasized.

With a “humid atmosphere,” thunderstorms can bring heavy rainfall, particularly in southeastern Quebec, she said.

“We’re talking about precipitation of 50 to 70 millimeters that can be expected,” she added.

“Obviously, these precipitation rates will vary locally because municipalities or cities directly in the path of the storm are likely to receive more precipitation, compared to a municipality a few kilometers further from the storm’s core.”

Once these weather conditions have passed, temperatures and humidity are expected to drop again on Friday.

Other areas further north, notably Mauricie, Saguenay-Lac-Saint-Jean, Abitibi-Témiscamingue, Outaouais, and the Laurentians, are under a “sometimes heavy” rain warning for Thursday and Friday.

Between 40 and 60 millimeters could fall through tonight, as the same system affects other regions of Quebec.

“It could fall with quite a high ratio. So it could eventually create torrential rains that could increase flash flooding of rivers in these regions,” says Cournoyer.

These areas are less affected by instability in the air, which makes them safe from a severe thunderstorm watch, says the spokesperson.

Once these potential weather conditions have passed, humidity should drop on Friday, as should temperatures, returning to seasonal normals. However, this could be short-lived.

“Starting on Saturday, depending on the prevailing winds and air masses, we’ll see a second push of warm air from the U.S. arriving over Quebec sectors,” says Cournoyer.

“The episode of milder temperatures won’t last long. Already for the weekend and early next week, we’re watching for a heat episode with humidex”, she concludes.

–This report by La Presse Canadienne was translated by CityNews