Study uncovers historic tornado outbreak

Special to Western News

Tree fall damage near the damaged property captured during the Sainte-Anne-du-Lac aerial survey conducted by PHB Arpenteurs-Geometres.

Following an extensive ground and aerial survey led by wind engineering experts at Western, it has been determined that the tornado outbreak of June 18, 2017 in southern Québec is officially the largest recorded in the province’s history and, consequently, one of the largest ever recorded in Canada.

On the historic day last summer, numerous supercell thunderstorms developed in southern Québec producing large hail, high winds and damaging tornadoes.

It was previously understood that a total of four tornadoes formed that day. But new data from Western shows the number was significantly higher.

Using advanced satellite imagery covering the known damaged locations, as well as all surrounding areas, Western’s Wind Engineering experts exhaustively studied the targeted tornado region (spanning more than 400 kilometres) to isolate any previously unknown tree falls. As a result of the survey, seven new tornadoes, previously undetected, were identified raising the total of confirmed tornadoes for the Québec tornado outbreak to 11.

Special to Western NewsPhotograph of the remaining foundation of the destroyed home in Sainte-Anne-du-Lac observed during the ground survey.

The survey was conducted by Greg Kopp, Joanne Kennell and Emilio Hong from Western’s Department of Civil and Environmental Engineering and David Sills from Environment and Climate Change Canada. It is a collaboration between Western and ECCC known as the Northern Tornadoes Project.

“Many Canadians don’t realize that we can have intense tornadoes in the northern regions of the country. The goal of our project is to identify as many of these as we can, so that we can better define the true risk in those areas,” explained Kopp, a Western Engineering professor and lead researcher for the Northern Tornadoes Project.

Ground surveys of the region were performed by the Quebec Storm Prediction Centre (QSPC) and Western. Both found significant damage to residential buildings in Sainte-Anne-du-Lac and Hébertville. The Western team rated the Sainte-Anne-du-Lac tornado as EF-3, which was the strongest tornado of the day, with a track length of 30.5 km and width of 1300 m. The Hébertville tornado was rated as EF-2, with a track length of 22.5 km and width of 900 m.

After the ground survey was conducted, aircraft flights were performed to capture high-resolution aerial images of the damage. Such imagery can show significant tree falls in remote and heavily forested areas that are often difficult to locate during ground surveys. These initial flights were performed over Sainte-Anne-du-Lac, Lac Noir, Lac des Cornes, Hébertville, and Lac de la Boiteuse from July 10-18, 2017. After analysis of the aerial imagery, it was clear that the entire tracks of the storms were not captured.

A second aerial survey was ordered over Sainte-Anne-du-Lac, which encapsulated the entire track of the tornado. This survey, led by Western, was conducted on Jan. 17.

The project also identified two tornadoes that occurred in northern Ontario in 2017 but had been previously undetected. Both tornadoes formed in the Dryden area, one on June 14, 2017, and the other on July 25, 2017.