TORONTO - Environment Canada says a storm that toppled trees and downed power lines across southern Ontario on Wednesday became more powerful than expected because of the time of day at which it occurred and the conditions that prevailed at the time.

Senior Climatologist David Phillips says the storm would likely have passed with much less notice if the cold front that caused it had struck earlier in the day, when temperatures and humidity levels were lower.

But when the cold front passed over the southern part of the province during the mid to late afternoon, Phillips says it encountered warm, moist air that gave the storm an additional boost.

Environment Canada received reports of uprooted or damaged trees around Lake Erie, in pockets throughout the Greater Toronto Area and in Algonquin Park.

Local bands of hail and heavy rain caused flooding in some cases, including Toronto's landmark Eaton Centre, where water gushed from the roof into the mall.

Provincial utility Hydro One reported that at one point as many as 47,000 customers were without power thanks to damage to local lines.