Wet & Unsettled Weekend Brings Threat of Severe Storms and Significant Rainfall to Southern Ontario
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As we approach the final weeks of summer, with the back-to-school season around the corner and the arrival of astronomical autumn just under a month away, it seems Mother Nature is continuing the trend of a wet summer. The upcoming weekend is set to bring multiple rounds of rainy weather, and by early next week, we might even get a taste of early fall-like conditions, with possible single-digit lows for parts of Southern Ontario.
Rain over the next few days will come in waves, starting Friday afternoon in Southwestern Ontario and lingering through the weekend. Thunderstorm activity will play a significant role in this weekend’s rainfall, potentially leading to localized totals approaching 80mm. The rain should taper off by early Monday, with Eastern Ontario seeing the last of the precipitation.
MODEL IMAGE FROM WEATHERBELL
As of Friday afternoon, the first wave of rain is already moving into Southwestern Ontario, extending into regions around Lake Huron and Georgian Bay. This cluster of rain and embedded thunderstorms is expected to gradually track eastward into the Golden Horseshoe and Central Ontario by Friday evening.
Rainfall amounts will be highly variable due to the thunderstorm component, but widespread totals of 5-15mm are expected by Saturday morning. Localized amounts could reach 25-50mm for areas that experience thunderstorm activity, though it’s difficult to pinpoint exactly where this will occur.
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Moving into Saturday, the rain will become less widespread, with a focus on Eastern Ontario and Southwestern Ontario during the morning hours. Eastern Ontario is expected to see lingering precipitation from Friday night’s first wave of rain.
We are also closely monitoring the risk of pop-up thunderstorms in Southwestern Ontario, extending into the Golden Horseshoe through late morning and early afternoon on Saturday. While these storms are expected to be mostly non-severe and primarily a rainfall risk, we can’t rule out a marginal severe threat, as the environment could potentially support some hazards, including hail and damaging wind gusts. An isolated tornado can’t be ruled out, though the risk is relatively low.
MODEL IMAGE FROM WEATHERBELL
More isolated pop-up thunderstorms are expected across Southwestern Ontario, the Golden Horseshoe, and Central Ontario throughout Saturday afternoon and evening. There is concern that these storms will be slow-moving, with some areas experiencing multiple rounds of storms in a short time frame. This could lead to a heightened flash flooding risk, particularly in more urban parts of Southern Ontario, such as the Greater Toronto Area.
Due to the localized nature of the rain on Saturday, some areas may not see a drop, while others could receive upwards of 50-75mm of rain. The heaviest rain appears to be concentrated along the Hwy 401 corridor between London and Toronto, with other pockets of heavy rain in Central Ontario. However, this is just a general idea from one model and could shift depending on where the storms develop.
There should be a break in the rainfall overnight Saturday for most areas, although a few localized showers are possible, particularly around Southwestern Ontario and the Golden Horseshoe.
MODEL IMAGE FROM WEATHERBELL
Similar to Saturday, pop-up thunderstorms are expected to return across Southern Ontario on Sunday morning and continue throughout the afternoon. These storms could bring additional heavy rainfall to the same regions affected by Saturday’s storms. Again, actual rainfall totals will vary significantly depending on where the storms hit, but some areas could see another 25-50mm (or more) by the end of Sunday.
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We are also closely monitoring the risk of severe storms in Eastern Ontario later in the afternoon and early evening on Sunday. Storms that develop here could bring damaging wind gusts, large hail, and potentially an isolated tornado. It’s still two days away, so much can change, but it appears that the Ottawa Valley, extending along the international border in Eastern Ontario, could see some marginally severe storms.
Rain is expected to continue overnight into Monday morning for Central and Eastern Ontario, with pockets of heavy rain and embedded thunderstorms. Southwestern Ontario and the Golden Horseshoe should finally see the rain taper off by late Sunday evening, with the rain ending in Eastern Ontario sometime Monday morning. This will give way to clear conditions for Monday afternoon and evening.
However, the calm weather will bring much colder air, with overnight temperatures plummeting into the single digits across much of Southern Ontario on Monday and Tuesday nights. Daytime highs will struggle to reach the 20°C mark on Tuesday and Wednesday, making for a much cooler week compared to what we’ve experienced this summer.
