Significant flooding ongoing in southern Ontario, tornado watch continues

Severe storms throughout the weekend could produce large hail and localized flooding. Storms prompted tornado warnings to be issued on Saturday morning.

4:56 p.m. ET - A tornado watch remains in effect across southern Ontario amid a severe storm threat Saturday. A tornado watch means that conditions are favourable for the development of tornadoes.

Pay close attention to the latest alerts in case the tornado watch is upgraded to a tornado warning in your area. Have a plan in place to seek safe shelter in case severe weather threatens your home, your office, or while you’re driving.

CURRENT TORNADO WATCHES (southern Ontario):

  • Caledon

  • Guelph - Erin - Southern Wellington County

  • Halton Hills - Milton

  • Innisfil - New Tecumseth - Angus

  • Newmarket - Georgina - Northern York Region

  • Orangeville - Grand Valley - Southern Dufferin County

  • Shelburne - Mansfield - Northern Dufferin County

southern Ontario tornado watch 5pm August 17 2024

The original article with the full forecast for Ontario continues below.

It's another busy weekend across Ontario as significant thunderstorms roll across parts of the province. A tornado was reported near the community of Ayr earlier on Saturday morning. Major flash flooding is ongoing across the region as some communities have seen 90+ mm of rain so far, with more on the way.

Any of the stronger storms today could produce large hail, torrential rainfall, and gusty winds. A tornado watch remains in effect for portions of the region.

Keep an eye on the radar and look out for watches and warnings that may be issued in your area.

DON’T MISS: PHOTOS: Damaging twister, flash flooding strike southern Ontario

Saturday storm risk into the Greater Toronto Area

Forecasters are tracking a low-pressure system moseying across the Great Lakes region to start the weekend. This low will trigger a risk for thunderstorms throughout much of southern and northeastern Ontario.

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Southern Ontario Saturday storm energy Aug 17 2024

Not everyone will see a thunderstorm on Saturday, but the threat is there with the combination of lift from the approaching system and instability amid the warmer airmass parked over the region. Many folks in the Niagara region may have already woken up to the sound of thunder booming outside during Saturday's pre-dawn hours.

The greatest level of instability will fall across southwestern Ontario and the Greater Toronto Area, lending these areas a potential for severe thunderstorms on Saturday. This risk includes Toronto, Hamilton, London, and Sarnia.

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Southern Ontario Saturday thunderstorm risk map AUg 17 2024

Saturday’s strongest thunderstorms could produce large hail, heavy rainfall, and strong wind gusts. Given the energy levels we’ll see over the region, some of the hail could reach toonie size, which is more than enough to cause damage to homes and vehicles.

While we don’t have as much atmospheric moisture as we did during significant flood events earlier this summer, the slow-moving nature of some downpours could lead to a localized flooding threat.

Storms shift toward Ottawa by Sunday

We’ll see a risk for thunderstorms continue into Sunday, with the potential for severe storms shifting farther into eastern Ontario.

Southern Ontario Sunday storm risk map Aug 17 2024

A widespread chance for pop-up thunderstorms will exist once again on Sunday. The potential for severe storms will creep into eastern Ontario, covering the National Capital Region.

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Any of Sunday’s stronger storms could produce large hail, heavy rainfall, and gusty winds.

However, there is some uncertainty whether or not the instability will remain south of the border or if it’ll creep into the Ottawa Valley. There’s also a non-zero chance that some of the storms may rotate with moderate instability and a bit more spin in the atmosphere.

Remain alert for watches and warnings issued in your area as you run errands and head out this weekend.

Stay with The Weather Network for all the latest on your forecast across Ontario.

Thumbnail image credit to Mark Robinson/The Weather Network.

WATCH: Damage on the ground after tornado touches down in Drumbo, ON