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Written by ClimateFast member H. R. (Bob) Bach P.Eng.. Bob has been  a resident of the Markland Wood neighbourhood in Toronto since 1979.

1.0 A Very Recent Event: On May 21, 2022, southern Ontario was struck by a weather system, identified by meteorologists as a “Derecho”. This is defined as follows:

“A widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a “mesoscale convective system”. 

Derechos can cause hurricanic or tornadic-force winds, actual tornadoes, heavy rains, and flash floods.

They move about as fast as some tornados, but instead of spiraling like a tornado or hurricane, the winds of a Derecho move in straight lines. That's where the storm gets its name; the word “derecho” in Spanish means “straight ahead”.

2.0: Damage in Southern Ontario: The May 21, 2022 Canadian Derecho was a high-impact event that affected the Windsor to Quebec City- Corridor, Canada's most densely populated region, with 15.6 million people (41% of Canada’s population).. Described by meteorologists as an historic Derecho and one of the most impactful thunderstorms in Canadian history, with winds up to 190 km/h (120 mph) as well as several tornadoes, it caused widespread and extensive damage along a path that extended for 1,000 kilometres (620 mi).

Three cities across southern Ontario declared a state of emergency. At least eleven people were killed, mostly by falling trees. Power outages affected an estimated 1.1 million customers, and thousands were still without power a week after the storm. Hydro Ottawa described the damage dealt to its power distribution system as more severe than the 1998 ice storm. 

According to an estimate published on June 15th by the firm Catastrophe Indices and Quantification (CatIQ), the insured damage would amount to C$875 million, that is, C$720 million in Ontario and C$155 million in Quebec. This Derecho ranks as the sixth costliest weather event in Canadian history in terms of insurance claims.

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