Short-lived summer in Ontario: Focus shifts to thunderstorms

The official Summer 2017 Forecast drops on Tuesday, May 23. Check back for a complete look at what the next 3 months have in store.


Digital writers theweathernetwork.com

Thursday, May 18, 2017, 4:54 PM

Midsummer heat has been warmly welcomed across southern Ontario, with a two-day streak of temperatures surpassing 30oC in some parts of the region.

But cooler conditions are ahead, along with a widespread risk of severe thunderstorms Thursday as the cold front moves through. Severe thunderstorm watches covered almost all of the south of the province in the afternoon, with some storms already sparking in areas further north in the early afternoon, and in most of the Greater Toronto Area by the late afternoon.

"The thunderstorms are expected to develop ahead of or along a cold front this afternoon or evening," Environment Canada said in an update to the watch.

A watch means severe weather is expected in an area, upgraded to a warning when severe thunderstorms are either imminent or occurring. 


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There's an especially high threat for isolated-severe storms particularly in the Ottawa Valley and the southwest, along with the potential for heavy downpours and damaging winds. In the north, particularly the Nickel Belt, some 20-30 mm is expected by Friday.

In the south, rain will end through Thursday night for the region.

Sunshine returns for Friday into the long weekend, though some 10 degrees cooler than the week's peak temperatures.

Victoria Day Long Weekend

The long weekend is set to start well, though somewhat cool in the GTA with an east wind off of Lake Ontario Saturday, warmer in cottage country.

But a new system set to track toward the Great Lakes will likely bring rain and storms, spreading into the northwest late Saturday and to the south early Sunday.

"Exact timing is still uncertain but looks like a couple rounds of showers and thunderstorms, though it doesn’t look like a washout for the south, with some sun mixed in and rain holding off until later in the afternoon and evening for Ottawa and Montreal," Weather Network meteorologist Dr. Doug Gillham said Thursday. "However, we can’t rule out passing showers during the afternoon across Southern Ontario."

Gillham says near to below seasonal temperatures will dominate next week, possibly lasting for much of the rest of the month.

"Warmer than the first half of May, but no sustained 20o+C weather in sight," Gillham says. "The pattern also becomes more unsettled again with next system of significance around Wednesday."

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Check back for details as we continue to monitor the forecast.

Have a great day!