Damage to a farmhouse on the west side of Highway 2A south of Didsbury, Alta. allowed researchers to determine it was struck by an EF4 category tornado with a wind speed of 275 kilometres per hour.Northern Tornadoes Project
A tornado that ripped across the western prairie near Didsbury, Alta., on Canada Day ranks as one of the most powerful the country has seen, said experts who were on the scene soon after the severe weather event.
According to an initial analysis of the damage left in the tornado’s wake, wind speeds during the event reached a maximum of 275 kilometres an hour.
That meets the bar for an EF4 tornado, a rare occurrence in Canada. Since 1902, only 20 other tornadoes are known to have reached a comparable strength anywhere in the country. Canada has also experienced one recorded case of an EF5 tornado, which took place in Elie, Man., in 2007.
Saturday’s EF4 tornado caused no fatalities and only one injury while it carved a 15.3-kilometre-long swath in a rural area between the towns of Didsbury and Carstairs. The relative lack of structures in the area may have helped to avert a far greater disaster.
“It could easily have hit either of those communities or gone through Calgary,” said David Sills, who directs the Northern Tornadoes Project at Western University in London, Ont. “It’s not that far away.”
Investigators with the project conducted a ground and drone survey of the damage on Sunday in collaboration with the Prairie and Arctic Storm Prediction Centre, part of Environment and Climate Change Canada.
Project members found that 12 residences were struck by the tornado, three of which were destroyed. One was a well-constructed house built in 1978 that conforms to current building codes. That house was directly in the tornado’s path and was flattened.
Connell Miller, a engineering researcher who led the survey team, said that rather than structural elements of the house being pulled apart by the tornado – a pattern that is often seen with weaker structures – the load-bearing beams of the house were simply snapped off by the ferocity of the wind. A woman taking shelter in the basement survived the home’s collapse.
The details of the structural damage to the house led to the EF4 designation, based on the Enhanced Fujita severity scale.
While damage to vehicles is not used as a criterion for measuring tornado strength, Dr. Miller added that another sign of the event’s power at that location was that it tossed a nearby combine weighing 10,000 kilograms about 50 metres, and then rolled it an equivalent distance further.
“It was a bit breathtaking to see this big piece of equipment just be reduced to a giant ball of metal,” he said.
The July 1 tornado was the strongest in Canada since the Alonsa twister in Manitoba in 2018, which killed one person and injured two others. In Alberta, it was the strongest since the Edmonton tornado in 1987, also known as “Black Friday Tornado,” which killed 27 people.
A combine weighing nearly 10,000 kg was tossed approximately 50 metres and then rolled another 50 by Saturday's tornado.Northern Tornadoes Project
Only 1 per cent of all tornadoes reported in Canada are strong enough to be classified as EF4 or the equivalent F4 designation that was used prior to 2013.
“The fact that we only see EF4 tornadoes across Canada every few years speaks to how rare they are,” said Terri Lang, an ECCC meteorologist based in Saskatoon who added that a confluence of atmospheric ingredients helped to energize the Canada Day twister.
A key goal of the Northern Tornadoes Project is to build a detailed database of all the tornadoes that occur in Canada and monitor the results for emerging trends in the frequency, intensity, location and time of year of tornadoes that may be affected by climate change or other factors.
Dr. Sills said that because EF4 tornadoes are so infrequent, there are not yet enough data available to show how such events may be affected by a warming climate.
Meanwhile, cleanup efforts resumed on the third day since the disaster with more than 100 volunteers participating. The tornado ravaged through the region’s agricultural community, affecting mostly farmers of hay, canola, wheat and barley, said Mountain View County Reeve Angela Aalbers.
The county has offered accommodation in hotels for those needing shelter but many residents decided to stay with friends and family, she said. The county is also assisting with the cleanup of roads and highways, while volunteers are helping at private properties.
So far, damages are considered insurable and do not qualify for the province’s disaster recovery funding, Hunter Baril, press secretary for Alberta’s Minister of Public Safety and Emergency Services, told The Globe and Mail in an interview on Sunday.
“The county will work with residents, and if there is any support that we can provide, as far as provincial lobbying for grant programs or something that may be useful to our residents, we will absolutely do that,” Ms. Aalbers said.
In January, a Globe and Mail investigation on building codes across Canada found that regulations on homes are inadequate in light of a recent rise in natural disasters related to climate change. Glenn McGillivray, managing director of the Institute for Catastrophic Loss Reduction, says houses in Canada can be built to tolerate up to an EF2 tornado, but the institute does not advocate for measures against stronger and rarer events.
“Once you get into the extreme of the extreme, it doesn’t really make a lot of sense to try to build for those that are so rare. You would have to take some pretty exceptional measures to protect against those types of tornadoes,” Mr. McGillivray said.