The Weather Network – Severe thunderstorms threaten southern Quebec, potential storm for Ontario

9:51 a.m. EDT

A severe thunderstorm watch is in effect for southern regions of Quebec, including Montreal and the Quebec region. Severe thunderstorm watches are issued when atmospheric conditions are favorable for the development of thunderstorms that can produce one or more of the following effects: large hail, damaging winds, torrential rain.

Severe weather marked the start of the week in Ontario, with a tornado warning in northern sections and damaging winds of 100 km/h reported in the southwest on Monday. The storm threat will redevelop even further east on Tuesday for the eastern and Quebec sectors. More on the storm’s impacts and the brief taste of fall ahead of the Labor Day long weekend, below.

READ MORE: PHOTOS: Savage storms with fierce 100 km/h winds sweep across Ontario

Tuesday: Threat of a thunderstorm early in the week amid an amplified jet stream

An amplified jet stream is expected to bring dramatic temperature swings to Ontario and Quebec this week as we transition from summer heat and humidity to a hint of fall. The same system helping to usher in cooler air also triggers a widespread thunderstorm risk in the area through Tuesday.

Severe storms swept through northern and southern parts of Ontario on Monday evening, knocking down trees and utility poles in parts of the southwest with winds of 100 km/h being recorded in Windsor and Sarnia.

WATCH: Summer or sweaters? Wild weather change on tap for Canada this week

The storm threat will move further east on Tuesday as instability builds in eastern Ontario and Quebec as cooler air filters into the Great Lakes.


The greatest threat of severe thunderstorms Tuesday afternoon will be confined to eastern Ontario, southern Quebec and the Niagara region, with torrential rains, strong gusty winds and large hail.

Looking ahead: Cooler early September, but warming for Labor Day weekend

Only one day in August was lower than the season. There will be a significant change in this temperature trend during the first days of September, which are expected to be cooler.

Forecasters will be watching for the risk of cold weather in northern sections pushing further south. On Thursday, an abnormally cold lobe of air is pressing south across northern Ontario, plunging temperatures as much as 10°C below the early September season near the Ontario-Quebec border.


It is likely that some communities will have daytime highs stubbornly stuck in the mid to upper teens, but farther south on the 401 Highway corridor low 20s will be more likely. The taste of early fall, however, is short-lived.

Beyond that, warmer weather will return over the Labor Day long weekend and continue into the following week for the start of the school year.

Thumbnail image courtesy of Paul Arnold, taken in Hamilton, Ontario.
Be sure to check for the latest weather updates for Ontario.

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