After a week that’s brought mostly sunshine and pleasant late summer temperatures to southern Ontario, a fall-like pattern will set up for the weekend with periods of heavy rain and thunderstorms threatening outdoor plans. This weekend will also see the perfect setup for waterspout formation, so it’ll be important to remain alert to the changing conditions.
The precursor to this will be a sharp cold front crossing southern Ontario on Friday, igniting a non-severe thunderstorm risk and ushering in a dramatic pattern change to chilly, October-like temperatures.
In fact, as temperatures hover just above the freezing mark across northeastern Ontario overnight Friday, it’s possible some people will even see wet snow mixed with heavy rainfall over the region.
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Don’t write off the summer season just yet, however, as pleasant late summer weather is expected to return and continue through the end of next week.
A strong cold front, supported by a potent upper level low, brings in widespread rain showers and a thunderstorm risk on Friday.
Above seasonal temperatures sitting in the mid 20s will span the region ahead of the front on Friday, but then will plummet into the teens throughout the weekend.
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Overnight Thursday, and into pre-dawn hours on Friday, the cold front cuts through the Nickel Belt and Lake Huron, pushing showers across the northeast, and an embedded thunderstorm risk onto the shores of Lake Huron and into extreme southwestern Ontario.
Through Friday morning, there’s a chance for showers across the Greater Toronto Area (GTA), as the thunderstorm risk remains in the southwest.
Through the afternoon, expect heavier showers and the risk for thunderstorms across much of the GTA, including Toronto, Hamilton and Niagara. Strong winds and small hail will accompany the rain in areas that see storms.
By the late afternoon, and through Friday night, heavier pockets of rain are expected for the east end of GTA, through eastern Ontario and into cottage country.
On Saturday, the heaviest rainfall pushes into western Quebec, with cloudy conditions and scattered showers lingering over parts of Ontario. There will be dry breaks in southern Ontario and the GTA, so Saturday won’t be a complete wash out, but will still require some planning ahead.
High temperatures however, will be 5-10 degrees colder behind the front on Saturday compared to Friday.
The upper low, and cold northwest winds on Saturday and Sunday will bring wrap-around and lake-effect rain showers across Georgian Bay, Lake Huron and parts of the GTA. Wind gusts could reach between 30-50 km/h.
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These cold northwesterly winds blowing over the relatively warm waters of the lakes will generate some instability below, with a good chance for waterspout development.
During the late summer and early fall are prime times to see waterspouts, as cooler air begins to settle in, but the lake temperatures are still quite warm. This creates a temperature gradient and instability between the air and lake surface, causing the air to rise rapidly, even outside of the presence of thunderstorms.
Waterspouts tend to be slow-moving or near stationary, but sometimes move onshore, where they can cause minor damage or injury. It is best to keep an eye on the weather warnings in your area, and adjust any outdoor plans accordingly.
Clouds will build across the GTA once again on Sunday afternoon, with scattered showers expected through cottage country and a slight chance of some light rain in the GTA. High temperatures will remain in the teens.
FORECAST: Pleasant late summer weather is expected to continue through the end of next week
The periods of heavy rain and thunderstorms throughout the weekend will bring a risk of localized flooding in low-lying and flood-prone areas.
