A severe thunderstorm that left parts of Toronto underwater last month will go down as the most expensive natural disaster in the history of the province, according to the Insurance Bureau of Canada.

Preliminary estimates suggest the July 8 storm resulted in about $850 million in insured property damage, outpacing a wind and rain storm that left a $650 million cleanup bill in August 2005.

“While these preliminary estimates are staggering, we do expect them to go even higher,” IBC Vice-President for Ontario Ralph Palumbo said in a press release. “The good news is that our industry was well prepared to handle our obligations to customers.”

The storm lasted only a few hours, but saw about 126 mm of rain fall on the city, triggering serious flooding that temporarily shut down the subway system and left about 300,000 customers without power.

The downpour also submerged several stretches of GO Transit track, trapping about 1,400 passengers on one GO train near Bayview and Pottery roads.

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