Environment Canada has confirmed the tornado was a Fujita scale one or F1 tornado that began somewhere near the Cambridge neighbourhoods of Little's Corners, and ended near Westover, with the most damage created in Kirkwall.
The national weather agency said the tornado caused a damage track that was about 15 km long and 300 metres wide. Damage was noted to trees but no injuries or fatalities were reported.
The tornado was the sixth confirmed during the 2011 season. The full effect of a sudden and damaging thunderstorm was still being investigated Thursday, after the storm produced lightning and funnel clouds that threatened many communities throughout southern Ontario.
Knocking out power
About 7,000 Hydro One customers in southern Ontario are still without power Thursday evening after wild weather knocked out electricity Wednesday night. Hydro One said 274 outages remained, the largest being in Dundas near Hamilton.
Up to 25,000 customers were without electricity immediately following the storm.
Environment Canada issued dozens of tornado watches and warnings from Windsor to Ottawa before high winds, lightning and torrential rain rolled in at around 7 p.m. The storms didn't let up until nearly five hours later.
Several funnel clouds were spotted in the small town of Forest, Ont., on the banks of Lake Huron. Residents watched as the storm rolled in across the water, bringing fierce winds and sharp blasts of rain.
The Lake Huron region is still recovering from a deadly storm last weekend, when the town of Goderich was struck by a powerful and relatively uncommon F3 tornado, devastating the town's centre and leaving one person dead.
The line of thunderstorms originating in Michigan had caused red alerts to be issued in several areas of southwestern Ontario region.
Residents of downtown Toronto were captivated as the CN Tower as a seemingly endless series of lightning bolts hit the giant structure. Others were disappointed to learn that safety concerns forced several attractions and businesses to close during the storm.
The Canadian National Exhibition shut down by 9 p.m. as the storm moved in and planes were grounded at Pearson International Airport between 7 p.m. and 9 p.m.
Rain and lightning at downtown BMO Field also forced the mid-game delay of a Toronto FC's Champions League game with FC Dallas. CONCACAF officials said the entire 90-minute game would be replayed Thursday morning with the visiting side's one-goal advantage being erased. Dallas defeated Toronto 1-0 in the replayed match.
Lightning also stuck a house in Toronto's north end, starting a fire that spread to a neighbouring home shortly before midnight.
No one was hurt in the blaze, but the fire caused an estimated $100,000 in damages.
Among the hardest-hit areas in the GTA was Burlington, where heavy winds knocked out power and tumbled trees in the downtown core.
According to Environment Canada, the storm averaged 1,000 lightning strikes every two minutes across southern Ontario.
The fierce winds and crackling lightning cut power to some 5,100 homes near Beachville, and 4,200 more homes and cottages near Bancroft. Both communities aren't expected to get their electricity back until noon.
Another 4,000 hydro customers lost power near Dundas, where power was expected to be fully restored by 4:30 p.m.
The weather system had moved further east by Thursday morning, bringing isolated and non-severe thunderstorms to eastern Ontario.
Scattered thunderstorms were also expected over northwestern Ontario Thursday night, with the possibility of damaging winds and large hail arriving by Friday morning.
With files from The Canadian Press
