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Warm air hovers over southern Ontario, fuels severe storm risk

Sunday, September 12th 2021, 1:46 pm - The weekend will end on a soggy note in extreme southern Ontario, with multiple rounds of thunderstorms possible Sunday, potentially reaching severe limits in the southwestern sections. There is also a very conditional, low-end, but non-zero tornado risk.

Saturday saw tornado-warned storms move through parts of northern Ontario, but for Sunday, the severe weather threat will be at the opposite end of the province. The storm potential will be confined to the western Greater Toronto Area (GTA) and areas southward, with the chance of some reaching severe limits in the southwest. While very low and conditional, there is a non-zero tornado threat, as well. Temperatures will be above seasonal once again, with a lingering humid air mass in southwestern areas Sunday that will make it feel closer to the 30-degree mark or higher for some. Beyond, a tricky forecast is in play for the first half of this week, with more storm chances. For more, read below.

SUNDAY: MULTIPLE ROUNDS OF STORMS POSSIBLE, SEVERE RISK IN SOUTHWEST

On Sunday, it will be the most southern areas of Ontario that will need to pay attention to the skies for thunderstorm potential, thanks to a sluggish boundary drifting across the region.

There is likely to be multiple rounds of thunderstorms in parts of the region, beginning in the early afternoon and continuing through the overnight. With moderate cape values, the severe threat is present in the southwestern sections, aided by a warm southerly flow.

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Areas stretching from Grand Bend to just shy of Port Colborne including Hamilton, and southward to just past Chatham, will see the potential for storms to reach severe criteria. Hazards with the more potent cells will be strong wind gusts, large hail and heavy rain. There is also a very conditional, low-end, but non-zero tornado chance, as well.

Temperature-wise, Sunday won’t be far removed from Saturday, with similar mid-20s for daytime highs in the south. However, the extreme southwest will be a bit warmer, with temperatures expected to hit or exceed the 30-degree mark in Windsor. The air mass will be a bit humid, as well, with feels-like values approaching or above 30 in several areas.

LOOK AHEAD: STORM RISK, FORECAST GETS TRICKY FOR FIRST HALF OF NEXT WEEK

Beyond the weekend, a tricky forecast for the first half of next week. Very warm and humid air attempts to push north into the region, but it is uncertain how far north the boundary will get before a cool front sweeps across the region.

Multiple rounds of showers and thunderstorms are expected with the two fronts. Tuesday will see another risk for severe thunderstorms in southern Ontario.

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"Another chance for severe thunderstorms will set up in Ontario on Tuesday, with the possibility of a line of potent and rotating storms developing. [However, it is] all dependent on the right atmospheric conditions and timing coming together," says Melinda Singh, a meteorologist at The Weather Network.

More sunshine and less active weather for the second half of the week and into weekend with a warming trend.

Warmer than normal temperatures are expected to dominate for mid- and late-September with the potential for a few days of very warm and possibly hot weather.

Thumbnail courtesy of Mally, taken in Vaughan, Ont.

Check back as we continue to monitor Ontario's forecast

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