Alberta’s Canada Day Tornado Rated EF4, Second-Highest Since Deadly Edmonton Tornado in ’87

July 1 tornado worst to hit province in nearly 40 years

People embrace after a tornado damaged homes near Carstairs, Alta., on July 1, 2023. The Canadian Press/Jeff McIntosh

The 275 km/hour tornado that left a path of destruction in Alberta’s Mountain View County on Canada Day has been declared by weather experts as the most powerful tornado to whip through the province in almost 40 years.

According to a preliminary assessment issued July 4 by Environment Canada, assisted by the Western University Northern Tornadoes Project (NTP), the tornado that ravaged 15 kilometres of land between Didsbury and Carstairs in just 30 minutes on July 1, was rated a EF4 on the six-point Enhanced Fujita scale—which starts at EF0 and goes to EF5.

The NTP, which detects and documents tornadoes in Canada, said witnesses captured video of the tornado, which developed at approximately 1:45 p.m. local time. It started as a thunderstorm near Sundre, then developed into a tornado southwest of Didsbury and moved eastward to north of Carstairs.

Two NTP survey teams travelled to Didsbury, joining with a team from Environment and Climate Change Canada and the Arctic Storm Prediction Centre, to investigate the weather event and conduct a damage survey.

“The survey teams found that there was enough evidence to rate the tornado damage at EF4, with a maximum wind speed of 275 km/h. The preliminary path length is 15.3 km and maximum path width 620 m,” the NTP said.

The last tornado in Alberta history with an equivalent rating was the Edmonton F4 tornado in 1987. That tornado was the strongest recorded tornado in Canada to have damage rated EF4 on the scale, which was implemented in Canada in 2013. According to NTP, the July 1 tornado is one of only three rated F/EF4 in Alberta, with the other one occurring June 25, 1915, in Grassy Lake.

Homes Damaged or Destroyed

During the Didsbury tornado, all the walls of a well-constructed house collapsed, contributing to how the tornado was rated. In addition, “various farm equipment was flipped and thrown at that property. This includes a combine harvester weighing almost 10,000 kg that was thrown at least 50 m, and then rolled for another 50-100 m after that,” said the NTP.

“Wind tunnel studies of another combine that was hit by a previous Canadian tornado suggest a wind speed of 230 km/h for just flipping a combine. Tree stubbing / debarking and ground scouring are also consistent with a high-end tornado.”

The tornado began as a thunderstorm near Sundre, and intensified as it approached Didsbury. Environment Canada said it appeared to weaken briefly before re-intensifying as the storm moved east.

Tornado-damaged homes are seen near Carstairs, Alta., July 1, 2023. The Canadian Press/Jeff McIntosh

“The heaviest damage (EF-4) was reported where the tornado crossed Highway 2A between Didsbury and Carstairs. The tornado weakened and dissipated near the QE2 Highway,” said Environment Canada.

The tornado caused extensive damage to multiple properties, destroying a number of homes and farm buildings. It caused significant damage to trees, power poles, and vehicles. Several dozen farm animals were killed and one minor injury was reported, apparently a cut suffered by a first responder.

Didsbury RCMP sent out an advisory initially stating that 14 houses were affected by the tornado. The initial RCMP report said five houses were completely destroyed. Carstairs and Didsbury firefighters attended the scene as well as the RCMP.

Environment Canada said the tornado caused damage to 12 homes, of which three were destroyed and four were left uninhabitable.

“The most notable damage occurred at the farm on the west side of Highway 2A. A well-constructed home was destroyed in this location with all exterior and above-grade interior walls knocked down.”

According to the report, a homeowner was in the house at the time and took shelter in the basement.

The RCMP said they found one woman trapped in her basement, with the entire house above her destroyed.

“Thankfully Carstairs Fire Department pulled her from the [rubble] and she only suffered minor injuries. No other people have been injured.”

RCMP said 25 cows and 20 chickens were killed by the tornado and one horse had to be put down.

Historical Tornadoes

Since 1915, eight tornadoes have been given an F3 rating or higher in Alberta:

June 25, 1915 F4 near Grassy Lake June 30, 1982 F3 near Rocky Mountain House July 8, 1983 F3 northwest of Lloydminster June 29, 1984 F3 near Athabasca July 31, 1987 F4 near Edmonton July 29, 1993 F3 near Holden July 14, 2000 F3 near Pine Lake July 23, 2000 F3 near Marwayne

The tornado on Canada Day is the second tornado in Canada to have damage rated at EF4 on the Enhanced Fujita Scale, with the other being an EF4 tornado in Alonsa, Manitoba, that also had a maximum wind speed of 275 km/hour.

Still, the NTP said that while the July 1 tornado may have been “climatologically significant,” it won’t make the list of Canada’s “top ten ‘worst’ tornadoes due to the single minor injury and limited property damage.”

“Across the country, there have been only 21 ‘violent’ tornadoes rated at F/EF4 or higher. One of these was Canada’s only tornado rated at F5 - the Elie, MB tornado of 2007. Most of the others (12) have been in southern Ontario. Saskatchewan and Manitoba have also experienced F4-rated tornadoes (3 in SK, all 1920 and earlier; 2 in MB from 1977 and 1994),” said NTP.