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QUEBEC | Severe weather threat

'Dynamic fall storm' slams Quebec with severe weather

Digital writers

Friday, September 21, 2018, 9:29 AM - A powerful fall storm will close out the last official day of summer with severe weather, with watches and warnings already coming into effect across Quebec and Ontario. The dynamic storm system could bring wind gusts near 100 km/h, along with a tornado threat as the storm pushes through. More on the timing and impact, below.

(Visit our Complete Guide to Fall 2018 for an in depth look at the Fall Forecast, tips to plan for it and a sneak peek at winter)


  • Severe thunderstorms over much Quebec on Friday with a deepening fall system
  • Heavy rain, damaging wind gusts, isolated tornado threat all on the table
  • Significant cool down for the official start to fall on Saturday, temperatures won't crack the 20°C mark


Friday marks the official last day of summer and right on cue, a big fall storm will end the season with a bang.

"We're tracking the risk for severe storms across Quebec on Friday, with damaging winds and a tornado threat for certain areas. This all comes in with a deepening and dynamic fall storm over the Great Lakes," says Weather Network meteorologist Erin Wenckstern.

With strong winds both at the surface and aloft, there's a heightened threat for these two things:

First, the strong winds will increase wind shear (wind speeds increasing and changing with height in the atmosphere), supporting the risk for supercell thunderstorms capable of producing tornadoes in southwestern Quebec on Friday (more on this risk below).

Second, these powerful winds circling the storm may rush down to the surface, raising the risk for damaging wind gusts. This type of setup is expected as a squall line -- an organized line of thunderstorms -- develops along the cold front in Quebec and blasts eastward.


A warm front will push through Friday morning across southern Quebec, leading to a period of rain and embedded, but elevated thunderstorms, spreading east through the morning and early afternoon hours. Then a break occurs across much of southern Quebec, including Montreal and Quebec City, where the majority of the day will be hot, humid and rain-free.

But as the atmosphere clears, it will begin to destabilize. Severe thunderstorms will begin to blossom and increase in intensity in the Ouatouais and Laurentians region, close to the Ontario border with supercells possible in the afternoon hours. The tornado threat will be greatest in this region, along with small hail, strong winds and heavy downpours. Into the evening, the squall line will develop along the cold front, sweeping west to east across western Quebec, approaching the Montréal, Trois-Rivières and Québec region around 7-8 pm. Expect thunderstorms along this line to be strong to severe, rumbling through mid to late evening, with damaging wind gusts over 100 km/h possible.

The system clears quickly, but gusty and cooler northwesterly winds will rush across Quebec in its wake.

By Saturday, the air will reflect our transition into fall, as temperatures fail to reach 20°C and we ring in the new season at 9:22 pm.

Our team of meteorologists will be LIVE tracking the storms over Ontario and Quebec Friday afternoon and evening, so be sure to follow The Weather Network on Facebook or download the app to get up to the minute details.

Be sure to check back as we continue to provide updates on this incoming system.


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