Alberta had a slow tornado season. That wasn't the case elsewhere in Canada

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Fall is well underway and with that, an end to tornado season in Canada.

This year's tornado season has stood apart from last year's sleepy summer for supercell thunderstorms, but in Alberta, tornado numbers are still relatively low.

"We did have eight tornadoes, and last year only three, but both of those are quite a bit lower than normal," says Kyle Fougere, a warning preparedness meteorologist with Environment and Climate Change Canada.

Looking at climatology between 1980 and 2009, Alberta averaged 15 tornadoes a year, Fougere says. Those climate numbers are updated for the latest 30-year window, with the 1990 to 2020 numbers expected next year.

But 2022 wasn't a slow year everywhere in Canada. Saskatchewan saw its busiest summer for tornadoes in a decade, with 25 confirmed. The historical average for Saskatchewan is closer to 18 tornadoes over the summer.

"It's actually the most tornadoes we've had in Saskatchewan since 2012, when they recorded 33 tornadoes," Fougere says.

So why the drastic difference between neighbouring provinces? And how are the numbers of tornadoes we see in a typical year shifting over time?

Slower season in the West

Alberta's low count has been a trend over the past decade. Fougere says the only time we saw more than 15 tornadoes in a season was in 2019, when there were 23.

But as we saw this summer in Saskatchewan, there hasn't been a tornado drought everywhere.

"Every year we do see a lot of variability in tornado numbers," says Fougere. "It's not that rare to see one province have a much different summer than the province next to it."

Early season landspout tornadoes,which are weaker and can form without strong thunderstorms,can drive up numbers.

Large-scale setups in the atmosphere such as expansive areas of high pressure, or persistent patterns in the jet stream also play a role, as was the case this year.

• How kinks in the jet stream can push our weather to extremes

"We had a big ridge of high pressure from about the second week of July onward over Western Canada," Fougere says.

Sinking air under those ridges generally means clear weather and not very many thunderstorms.

"That likely played a role for why Saskatchewan had more. They were kind of more downstream of the ridge."

Other atmospheric conditions like heat and humidity can affect tornado formation, as well as wind shear the change in direction or speed of the wind as you move higher in the atmosphere. Fougere says even wildfire smoke can play a role.

"Smoke will limit the incoming solar radiation and so you get less heat, which provides the energy for these thunderstorms."

The new normals

Although this year solidified Saskatchewan as a tornado hot spot, the historical trends are showing a change.

Francis Lavigne-Theriault is a research assistant with the Northern Tornadoes Project (NTP). The research initiative out of Western University works with Environment and Climate Change Canada to rate and record every tornado across the country.

The project is now building a database analyzing every tornado in Canada since 1980. Researchers are revisiting the events and adding more detail to better understand how numbers are trending.

"The averages for each province have changed," says Lavigne-Theriault.

He says the number of tornadoes over the last 30 years has declined, and their locations are shifting too.

"Saskatchewan used to be the capital of tornadoes in Canada the most tornadoes on average. And now it's Ontario, over the last 30 years."

As for the strength of the tornadoes that do happen, Lavigne-Theriault says those trends are harder to pin down.

In the study, researchers found there was an increase in the number of tornadoes that are ranked as an EF-2 or higher.

He says that increase is likely due to increased monitoring by projects like the NTP, and changes in population density across Canada.

"People are living where they didn't used to live," he says. "They're building man-made structures, so there's more likely a tornado will hit a populated area now than 30 years ago."

The full NTP database rewriting Canada's tornado history is still in the works, but should be made public by the end of this year on the project's website.

Alberta's strong storms

Though the number of tornadoes in Alberta was not impressive this year, the strength of the storms was notable.

Tornadoes in Canada are rated according to the enhanced Fujita (EF) scale. It ranges from EF-0 to EF-5. The more damage from the storm, the higher the rating.

• Surveying the damage: How tornadoes are ranked after the sky clears

This year, Alberta saw two EF-2 tornadoesone in Bergen, about 100 kilometres northwest of Calgary, in early July, and anotherlater that month in Redcliff, near Medicine Hat.

"The last time we had EF-2 tornadoes was in 2019 and I believe there were six of them that formed," says Fougere.

An EF-2 tornado may rank on the lower end of the EF scale, but it will still pack a punch.

"You'd have expected wind speeds between 180 and 220 kilometres per hour ... that's where you can see entire roofs lifted off of houses."

And higher-ranked tornadoes on the Prairies are less common. To rate a high ranking, a tornado must have damaged trees or structures, and on the southern Prairies, there are more open spaces.

"The likelihood is these tornadoes are not going to hit something when they form," says Fougere.

"They get rated as a default EF-0 because they don't do any damage."

Fougere adds that tracking tornado numbers, damage and location is essential to keeping the public safe; to determine where they are most likely to hit.

"We're constantly reviewing," he says."What creates the weaker tornadoes compared to the strongest tornadoes, and what factors would play into those, so that we can try to have the most accurate forecasting possible."

Our planet is changing. So is our journalism. This story is part of a CBC News initiative entitled "Our Changing Planet" to show and explain the effects of climate change. Keep up with the latest news on our Climate and Environment page.