A multi-day thunderstorm threat will bubble up across Ontario heading into the weekend, with humidex values surpassing 30 before cooler, more seasonal air arrives next week.
Some forecast uncertainty remains, particularly with storm severity and locations impacted. Be sure to stay up-to-date on any changing conditions and weather alerts in your area.
Thursday: Isolated thunderstorms expected
A slow-moving low pressure system is lifting a warm front into southern and parts of eastern Ontario. Pop-up and isolated storms are expected Thursday afternoon and evening, with areas like southwestern Ontario, south-central Ontario, the Greater Toronto Area (GTA), and Niagara at risk for thunderstorms producing heavy rain and small hail.
Isolated storms may result in highly variable rainfall amounts, with some areas seeing up to 30+ mm under localized cells.
Late Thursday evening, the centre of the low pressure system will move into southwestern Ontario, bringing rain and embedded thunderstorms that could last overnight into Friday.
Friday: Heavy rain could impact morning commute times
Heavy rainfall is possible Friday morning into the early afternoon in areas including London, Hamilton, Niagara, and parts of the western GTA.
While drier conditions may occur by early Friday evening, a renewed risk of storms is possible later that night in southwestern regions.
Saturday: Strong low with additional thunderstorm risk
On Saturday, a stronger low from northwestern Ontario will bring additional thunderstorms, with some severe storm potential in northeastern Ontario and along a cold front tracking across southern and eastern Ontario. Kingston through Ottawa could see severe storms by Saturday afternoon.
This system may carry upper-level wildfire smoke from British Columbia and Washington state, adding to the complexity of the forecast.
Stay tuned for updates as higher-than-average forecast uncertainty remains, particularly with storm severity and locations impacted.
An August cooldown is coming
Next week will begin with near-seasonal temperatures before trending cooler by mid-to-late week. Below-seasonal temperatures are expected to persist through the weekend and into the third week of August.
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While a few rounds of showers and thunderstorms are likely, significant rainfall totals are not anticipated.
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