Was that a tornado? Basic guide to identificaiton

On Wednesday night, Environment and Climate Change Canada and the Northern Tornadoes Project (NTP) at Western University confirmed that Ontario and Quebec were hit by at least four tornadoes.

NTP Executive Director David Sills explained that this week's tornadoes were quickly confirmed because teams had video evidence clearly showing a tornado causing damage.

"Last night, there was evidence both in Ontario and Quebec of a tornado based on video," he said. "It was backed up by radar, and also people on the ground reporting damage. So we didn't have too much of a problem confirming tornadoes in Ontario, Quebec last evening."

Violently rotating column of air

To be classified as a tornado, the funnel cloud must be travelling at least 90 km/h, which shows evidence that it could produce damage.

"Basically, it's a rotating column of air that's connected to the cloud base and connected to the ground, and has damaging winds associated with it," said Sills.

Storm damage is seen in Tres-Saint-Redempteur, Quebec on Tuesday, May 28, 2024 after a suspected tornado went through yesterday evening. (Ryan Remiorz/The Canadian Press)

Environment Canada uses the Enhanced Fujita (EF) scale, which goes from EF rating 1 (90-130 km/h) to 5 (315 km/h or more).

"The EF-scale employs a large number of damage indicators, ranging from residential housing to office towers to trees," Environment Canada says. "Wind speeds are more accurately related to wind damage thanks to an expert elicitation process that involved the meteorological, engineering and architecture communities."

Tornado or a downburst

Sills said the first thing teams need to do is make sure the phenomenon is not something else.

"A lot of times, when we get reports of damage, the first thing we need to do is determine if it was a tornado or a downburst that caused the wind damage," he said. "The patterns that are produced by those two different phenomena are quite different."

In a tornado, the wind is coming in towards the bottom of the storm and travelling up.

Multiple homes have been damaged as a tornado appears to have touched down in Rigaud, Que. (Baradaran Glady)

A downburst is the opposite: the wind starts at the top and spreads out when it hits the ground.

"You've got one pattern that's kind of a converging pattern, and usually you get a narrow, long path with a tornado, whereas with a downburst it's a diverging path, so all the trees or whatever are pushed out from a central point," he said.

The NTP says most showers and thunderstorms produce downbursts and that these can interfere with aircraft taking off or landing.