Twenty-one years ago today, southern Ontario lived through one of the costliest weather disasters in the province's history — a muggy Friday afternoon that spawned three tornadoes and flooded parts of the Greater Toronto Area with rainfall that surpassed the deluge from Hurricane Hazel's remnants in 1954.

The insured damage from the Aug. 19, 2005 storms likely exceeded $500 million, according to The Weather Network, citing figures from Public Safety Canada. At the time, it ranked as Ontario's second-costliest disaster, behind only the 1998 ice storm.

A triple tornado outbreak

The trouble began when a centre of low pressure moved over Lake Huron, setting the stage for severe weather across southern Ontario through the morning and afternoon. Warm, humid air flowing up from the south fuelled towering thunderstorms, while strong winds aloft added a tornado threat.

A powerful tornado touched down in Miverton around the lunch hour, producing F2 damage as it tracked northeast toward Conestogo Lake. Less than an hour later, the same storm system generated a second F2 tornado in Salem, damaging homes, farms and trees as it moved toward Lake Belwood.

Six people were injured across the two twisters, though officials reported no fatalities. A third tornado, rated F1, struck near South Easthope later that afternoon and caused no reported injuries.

A report filed after the storm captured just how violent the winds were. One of the tornadoes, it noted, "drove a ballpoint pen seven centimetres deep into a tree, splitting the trunk" on an area farm.

Rainfall that outdid Hazel

For residents of the GTA, the rain was the bigger story. Exceptionally heavy downpours triggered major flash flooding across parts of the region.

An observer in Thornhill recorded 175 millimetres of rain in a single hour, while an Environment Canada office in Downsview logged 100 millimetres in one hour. Those staggering rainfall rates reportedly exceeded the flooding rains that arrived with Hurricane Hazel's remnants in 1954 — the storm that remains a benchmark for disaster in the Toronto area.

Thousands of claims

Public Safety Canada stated that insurance companies received more than 15,000 claims related to wind or flood damage from the event, and that total losses likely topped $500 million.

In the two decades since, a string of costly storms has pushed the 2005 outbreak further down the ranks of Ontario's most expensive disasters. But for those who waded through flooded streets in Thornhill and Downsview that afternoon, Aug. 19, 2005 remains a day that measured up against Hazel itself.