Ontario preparing for what could be one of the strongest storms of the year

September is kicking off with a bang, as Ontario braces for a multi-day stretch of severe thunderstorms that could bring torrential downpours, damaging winds, and even isolated tornadoes across the province this week. 

According to The Weather Network's latest report, a low-pressure system in northwestern Ontario could result in severe thunderstorms on Tuesday, with the possibility of heavy rain, strong winds, and large hail. 

The multi-day event is set to begin on Tuesday afternoon, with isolated thunderstorms near Georgian Bay and Lake Huron. While the storms could potentially move towards the GTA and the Niagara Region, short bursts of precipitation (between 30 and 60 minutes) are much more likely here. 

Latest HRRR model is doubling down on tomorrow's severe weather potential across Southern #Ontario

Could be the most significant event of the year

Continues to show maxed out Tornado parameters east of Lake ##Huron

Will continue to monitor and post updates #OnWX #ONStorm https://t.co/9AzEBWvEPh pic.twitter.com/wrMz2RT79n

— WxOntario (@WxOntario1) September 1, 2026

The weather will become more unsettled on Wednesday, when a sweeping cold front from Michigan arrives in Ontario. This system will increase the potential for severe weather across southern and eastern Ontario, with risks of "torrential downpours, damaging winds, large hail, and the possibility of isolated tornadoes," according to the network.

"Morning rain may impact the GTA and Highway 401 corridor, with severe storms expected through the afternoon and evening," the report reads.

"The timing of Wednesday's storms remains uncertain. Storm activity is expected to develop across cottage country and into Quebec by early afternoon. Prefrontal rain could impact areas from the GTA to London earlier in the day."

Wednesday's daytime high is expected to feel like 37 C with the humidity, while Thursday's peak temperature of 25 C will feel more like 31 C.

Widespread Severe Thunderstorms continue to look likely tomorrow across a large portion of SW #Ontario and into parts of the #GTA

At this point, the circled area is at greatest risk of seeing the strongest storms

Torrential rain, large hail, damaging winds and tornadoes are all… https://t.co/9S570IoJkH pic.twitter.com/7AlFreRCuN

— WxOntario (@WxOntario1) September 1, 2026

The event is expected to come to a conclusion on Thursday, when — minus a few potential showers in the morning — precipitation will finally cease. Between Friday and Sunday, sunny conditions are expected in the GTA, with comfortable daytime highs between 23 C and 25 C. 

Between Tuesday's high of 28 C and Sunday's overnight low of 11 C, Toronto's temperatures will swing by 17 C over the course of just a few days. 

Despite the sunshine over the weekend, The Weather Network warns that showers and thunderstorms could return just in time for Labour Day, as more humidity builds up throughout the region.