Top ten weather stories for 2005: story three

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3. Ontario's Most Expensive Weather Disaster

On the afternoon of August 19, a line of severe thunderstorms tracked eastward across southern Ontario from Kitchener to Oshawa, including the northern half of Toronto. In its wake, the storm left a trail of damage that, according to the Insurance Bureau of Canada, represented the highest insured loss in the province's history, exceeding $500 million. That's more than two and a half times Ontario's losses during the infamous ice storm of 1998 and the second largest loss event in Canadian history.

Literally dozens of thunderstorms were popping up at any one time. At its worst, the system spawned two F2 tornadoes with gusts between 180 and 250 km/h. The first tornado tracked through Milverton to Conestogo Lake (west of Elmira). The second moved from Salem to Lake Bellwood (north of Guelph). The twisters uprooted hundreds of trees, chewed the limbs off of countless others, downed power lines, tossed cars and trucks aside, and ripped into several homes, cottages and barns. To illustrate the storm's incredible force, at one farm, the twisting winds drove a ballpoint pen seven centimetres deep into a tree, splitting the trunk.

Although a rare tornado warning was issued for Toronto, the storm packed a different wallop as it approached from the northwest. The storm featured torrential rains, quarter- to golf-ball size hail, strong straight-line winds and flash flooding. During the height of the tempest, wind gusts peaked at 72 km/h and there were 1,400 lightning strikes per minute. However, it was the flash flooding that caused the greatest destruction. The storm dumped 103 mm of rain in one hour across a swath of North York and surrounding area. That compares to 53 mm in one hour from Hurricane Hazel in 1954. At Environment Canada's Downsview offices, 130 mm of rain fell - 100 mm in less than an hour - an unprecedented amount for any storm in Toronto, and easily greater than the one in one hundred years storm. The deluge flooded two floors of the Downsview building, prompting employees to huddle in the basement and interior auditorium in order to ride out the storm. A block or two to the north in Thornhill, a weather watcher emptied her rain gauge at 175 mm. Around the city, torrential rains snarled traffic and stranded drivers. Fire services responded to more than 1,000 calls. In one dramatic scene, marine services personnel rescued four people who fell into the fast-moving currents of the Don River.

An early tally found that there were over 15,000 insurance claims submitted for sewer backups caused by torrential rains and for structural wind damage. Not included in the insured losses were enormous infrastructure damages across the city. For example, about 30 m of Finch Avenue West was washed out. Repairs had still not been completed by the end of the year.

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