Severe Storms and Isolated Tornado Risk Saturday in Southern Ontario With Great Lakes Waterspout Outbreak This Weekend

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As the clock ticks down on the final weeks of summer across Southern Ontario, we’re set to get a taste of fall-like weather later this weekend that may have you reaching for a pumpkin spice latte.

That cooler weather will also bring an increased risk of waterspouts over the Great Lakes as we enter the time of year when waterspout activity becomes more common.

But first, we must get through weather more traditionally associated with summer, including the risk of severe thunderstorms developing on Saturday afternoon.

These storms could bring damaging wind gusts, large hail and an isolated tornado threat. The tornado risk will be highest in Deep Southwestern Ontario, particularly near the southeastern shoreline of Lake Huron and around the London area during the late afternoon and early evening.

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Another concern is the potential for flooding, especially along a corridor extending from London through Kitchener and the Greater Toronto Area into Barrie.

Some models show storms repeatedly regenerating over this region for several hours during the evening. Rainfall totals of 50 to 100 mm could occur in the hardest-hit areas, with locally higher amounts possible.

In the wake of the storms, a much cooler Sunday is expected across Southern Ontario. Many areas could struggle to climb above 20°C during the afternoon.

This cooler air is expected to linger into the beginning of next week, making for a chilly start to the day on Monday and Tuesday.

DATA FROM WEATHERBELL

A complex of storms is currently developing over Michigan as of early Saturday afternoon. This activity is expected to track across Lake Huron and into areas southeast of the lake by late afternoon.

Additional isolated storms may also develop ahead of the main line.

If isolated storms develop, they could become supercells capable of producing all severe weather hazards, including up to toonie-sized hail, damaging wind gusts and an isolated tornado.

The strongest environment appears to be around London and northward into Huron and Perth counties during the late afternoon and early evening.

Around the dinner hour, the focus for storm development is expected to shift to the corridor from London through Kitchener and the Greater Toronto Area into Barrie.

Storms may repeatedly track over the same locations for several hours, leading to a risk of localized flash flooding.

By this point, the main severe threat will likely be damaging wind gusts as storms become more linear. However, an isolated tornado can’t be ruled out, especially earlier in the evening before sunset.

Storms are likely to linger beyond midnight, but most should become non-severe by that point.

Flooding could remain a significant concern during the early overnight hours, especially across urban parts of the Golden Horseshoe and Niagara Region that have already experienced substantial flooding this summer.

DATA FROM International Centre for Waterspout Research

Conditions are also expected to become favourable for waterspout development over the Great Lakes this weekend.

The highest risk appears to be focused on Lake Erie and southern portions of Lake Huron. Some waterspout activity may also occur over Georgian Bay, Lake Simcoe and Lake Ontario.

According to the International Centre for Waterspout Research’s latest forecast, the waterspout risk is expected to peak on Saturday afternoon and evening before continuing into Sunday morning and afternoon.

We’ve already received reports of at least one possible waterspout this weekend.

Instant Weather partner Michigan Storm Chasers received a report of a potential waterspout near Harsens Island, Michigan, on Saturday morning. Harsens Island is located directly across the border from Walpole Island in Ontario, and it may have crossed over the border at some point.