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Ontario multi-day thunderstorm and flood risk

Updated 2 times since CLSTR started tracking revisions of this situation.

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2026-08-04 21:54 UTC → 2026-08-21 23:48 UTC · added removed

Ontario multi‑day multi-day thunderstorm and flood risk

Late July 2026 saw Environment Canada lift a yellow severe thunderstorm watch for southwestern Ontario, warning that heavy rain could exceed 50 mm and raise flood risk from the Greater Toronto Area northward to Georgian Bay. Early August brought the forecasted thunderstorms, prompting special weather statements and rainfall warnings for the GTA, Niagara Region and cottage‑country cottage-country communities, with expected totals of 50‑80 50-80 mm. The threat materialised over the August 1‑2 1-2 weekend. Record rainfall fell across southern Ontario: the Quinte region received up to 80 mm, while the Niagara Peninsula saw localized totals above 100 mm and St. Catharines recorded 257.7 mm in the preceding week. Rivers peaked, prompting Quinte Conservation to operate watershed dams and issue water‑safety water-safety advisories. St. Catharines declared a state of emergency on August 3 due to damage to homes and infrastructure. A brief tornado warning was issued in the Niagara region, with minor tree damage reported in Kemptville. Authorities continue to urge residents in flood‑prone areas to secure property, check sump pumps, clear drainage, and avoid fast‑flowing water until river levels recede. The multi‑day storm In late August, a new slow-moving weather system remains prompted further alerts. The Niagara Peninsula Conservation Authority issued a flood alert for the dominant driver Niagara Peninsula, southeastern Hamilton, and eastern Haldimand County, forecasting 40 to 60 mm of localized rain between August 22 and August 24. While major flooding across the region. in large watercourses was not anticipated, officials warned of flash flooding in urban areas. Simultaneously, Environment Canada issued a special weather statement for Toronto, expecting heavy rain exceeding 50 mm and two rounds of thunderstorms.

Versions

  1. 2026-08-21 23:48 UTC Ontario multi-day thunderstorm and flood risk
  2. 2026-08-04 21:54 UTC Ontario multi‑day thunderstorm and flood risk
  3. 2026-08-02 21:31 UTC Ontario multi‑day thunderstorm and flood risk

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