As heat waves grip parts of Canada, experts say extreme heat and humidity could also fuel severe thunderstorms and even tornadoes.
Heat waves in Canada are becoming more frequent and intense, increasing the risk of these dangerous storms.
One of those storms hit the Prairies over the weekend, with tornadoes reported in parts of Saskatchewan after a humid heat wave.
“We often get very severe thunderstorms, usually in the afternoon, during periods of extreme heat, especially because of the humidity,” says atmospheric physics professor Kent Moore of the University of Toronto.
“If these are really severe thunderstorms, then tornadoes can also develop. So, there is a possibility that during a heat wave you will get a tornado thunderstorm.”
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Environment Canada sent warnings Tuesday to several provinces, including parts of Ontario, Quebec and Manitoba, where temperatures ranged from 30 to 40 C when humidifiers were used.
Summer typically brings warmer temperatures, but climate change or global warming causes peak temperatures to be higher than they would otherwise be.
“The extreme heat we are experiencing today is twice as likely due to the effects of global warming,” Moore says. “It’s probably two to three degrees warmer now than it would be without global warming.”
Environment Canada defines extreme heat or heat waves as two or more consecutive days in which daytime temperatures reached heat warning thresholds and there was no decrease in temperature at night.
He adds that these heat events “are one of the known consequences of climate change.”
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Moore says heat waves are typically caused by high-pressure systems in the atmosphere that compress and heat air downward and also draw moisture from regions such as the Gulf of Mexico.
The combination of intense heat and moisture in the atmosphere creates not only heat waves, but also ideal conditions for thunderstorms to develop.
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Environment Canada has issued heat warnings for most of Canada.
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Global News meteorologist Anthony Farnell says this particular heat wave can be classified as a “heat dome.”
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“A thermal dome is like putting a lid on a pot of boiling water. It traps heat (in this case solar radiation) and feeds itself day after day until the dome breaks,” he says.
“Severe thunderstorms can also form around a ‘ring of fire’ surrounding a thermal dome.”
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From heat waves to tornadoes
Heat is not a direct cause of tornadoes, but warmer air contains more water vapor, which leads to thunderstorms, Moore said.
“When it gets hotter, the atmosphere can hold more water vapor, and water vapor serves as fuel for the atmosphere,” he says.
“Most weather systems operate primarily on the energy that is released when water vapor condenses from gaseous to liquid form.”
Environment Canada says thunderstorms “can produce very strong winds, hail, heavy rain and sometimes even tornadoes.”
“Tornadoes can produce some of the highest wind speeds on the planet. Most Canadian tornadoes have maximum wind speeds of less than 180 km/h, but they can still cause serious damage.”
These storms can not only bring tornadoes, but also cause flooding from heavy rain.
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Flooding has severely affected parts of the Prairies, Montreal and Ottawa in recent weeks, following heavy rainfall from storms that hit communities and city centers.
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Are tornadoes becoming more common?
Although extreme weather events are becoming more frequent and severe in nature, tornadoes remain extremely difficult to predict and document.
“We don’t get a lot of severe thunderstorm warnings,” Moore said. “It’s possible that Environment Canada will issue warnings as they start to develop, but they’re much harder to predict. And I think tornadoes are still inherently unpredictable.”
Environment Canada says it can issue alerts and warnings, including for tornadoes, but those warnings can come in less than 30 minutes.
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Record-breaking heat hits Saskatchewan and Manitoba
It can be difficult to predict when and where tornadoes will form, but tracking of storms and tornadoes is improving.
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David Sills is the director of the Northern Tornado Project at Western University’s Canadian Severe Storms Laboratory and a former meteorological scientist at Environment Canada.
In a statement to Global News, Sills said his research team at the Northern Tornado Project has been collecting data since 2017 and has been able to nearly double the 30-year average number of tornadoes regularly recorded across Canada.
Sills says long-term data doesn’t show as much of an increase in the frequency of tornadoes in the Prairies as in Ontario and Quebec, but there has been a noticeable change recently, Sills said.
“The year-to-year variation in the number of tornadoes is quite high depending on the region. This year, it is the Prairies that seem to be locked in stormy weather and have had multiple tornadoes. But next year it could be the other way around.”
Storms and the tornadoes that can come with them are more common in a geographic region of North America commonly referred to as “Tornado Alley,” and parts of Canada are located along this corridor.
“Tornado Alley, which runs through Oklahoma, Kansas and Michigan, is kind of where most tornadoes form. Ontario is at the very end of that Tornado Alley,” Moore says.
“We’re also seeing more thunderstorms in the West now. So Alberta, Saskatchewan, Manitoba are also seeing more tornadoes. And again, that’s largely because the thunderstorms are more active now than they used to be.”