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Lingering storm risk in Ontario precedes forthcoming cooldown

Monday, August 17th 2020, 5:29 am - Another round of thunderstorms is possible on Monday in southern Ontario, ahead of a noticeable cooldown in some areas by Tuesday.

After an unsettled end to the weekend in southern Ontario, conditions may again trend that way for Monday, though the risk for storms will diminsh somewhat and temperatures will remain seasonal. The risk for storms will cover all of southern and northeastern Ontario, and they may bring heavy rainfall, but should be non-severe in nature. Come Tuesday, there will be a slight cooldown, more so for eastern Ontario and cottage country, where temperatures will be in the low 20s, even the upper teens in some areas. For a closer look, see below.


  • Thunderstorms possible Monday, but non-severe in nature
  • Cooldown begins Tuesday, but brief warmup for end of the week
  • More storm risk next weekend
  • Keep on top of severe weather ALERTS in your area


Though the cold front that triggered some passing storms Sunday has exited the province, a boundary right on its heels will bring the widespread, but non-severe, risk for thunderstorms Monday, appearing for most people in the afternoon and evening.


They may spark up in the late morning in parts of northeastern Ontario, while the chance will be prevalent across the south during the afternoon hours. CAPE values will be lower than expected, so any that do develop should remain below severe criteria.

Temperatures will still be seasonal Monday, with daytime highs sitting comfortably in the low- to mid-20s across the south.


On Tuesday, temperatures will take a bit of a dive, though not too sharpy, with humidity subsiding, as well. Daytime highs in the GTA and southwest won't fall too much from Monday, with temperatures in the mid-20s still, but eastern Ontario and cottage country will be closer to the 20-degree mark, even dropping into the upper teens in some locales.


While there won't be any major weather-makers in the province, some light showers are possible in northeastern Ontario through the Nickel Belt region, as well as along Lake Huron shores, as a result of lake breeze convergence. Extreme eastern Ontario, along the Quebec border, may see a non-severe thunderstorm as Monday's system stalls.

Beyond Tuesday, a brief warming trend is expected at the end of the week and into the start of the weekend, before another cold front tracks across the region on the weekend. This will bring another round of showers and thunderstorms, followed by a few more days of cooler weather.

"However, summer is not over – an abundance of summer weather is expected during the month of September," said Weather Network meteorologist Dr. Doug Gillham.

Keep an eye on the forecast as we continue to monitor Ontario's weather outlook.

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