The path of a severe thunderstorm that swept through Calgary on Sunday has been mapped out, and researchers say the city escaped catastrophic damage from the hail that accompanied the storm. Researchers at the Canadian Severe Storms Laboratory at Western University in London, Ont., dispatched a Northern Hail Project (NHP) team to investigate the storm that struck the city on July 13, which rolled in from the northwest and crossed the city in just over half an hour. Using drones, hail sensors, radar and on-the-ground surveys, the team determined the storm formed northwest of Waiparous, Alta., just before 6 p.m. and developed supercell characteristics as it crossed Highway 22 around 7:10 p.m. Hailstones up to 20 millimetres in diameter were recorded at that time. By 7:40 p.m., the storm had entered Calgary’s northwest and passed through the city at a speed of 50 to 55 km/h, exiting south of Chestermere at 8:18 p.m. The largest hailstones recorded in the city were between 30 and 45 millimetres in diameter — ranging in size from toonies to golf balls. Gusts of 45 to 50 km/h were reported in the hail core, with wind speeds at Calgary International Airport reaching 93 km/h. Matthew Woodward, a hail researcher and Alberta damage survey lead for the Canadian Severe Storms Lab, said the NHP’s goal is to understand the impacts of hailstorms and how often they occur. “If we know for a period of time how often hail events occur in certain areas, we can forecast risk, and we can forecast how better to prepare for these events in the future,” said Woodward. He said the team saw “quite a bit of siding damage, especially to PVC siding, as well as tree shred,” in the areas hardest hit by the storm, but more analysis is needed before reaching conclusions about roof and vehicle damage. Woodward said the most intense area of radar reflectivity during Sunday’s storm was just east of Nose Hill Park, which prompted the team to focus their initial damage survey there. “It only went through the city in about 30 minutes, so fairly quickly to cover that much area, as compared to last year’s storm, which was in Calgary on the north end for much longer,” he said. Neighbourhoods such as Highland Park, Highwood and Greenview were among those most affected. The NHP team plans to continue forensic surveying for two days, going door-to-door, taking drone images and examining physical evidence to estimate hail size, wind direction and storm intensity. “We’ll measure things like holes in the siding, how large they are, which sides of the building these damaging hailstones were on … scuff marks on electrical boxes, bark taken out of trees, any damage to roofs, any damage to vehicles,” said Woodward. “Just so we can try and trace back hail size and intensity in different neighbourhoods.” The city’s hail-monitoring infrastructure also provided useful data. “There’s a number of sensors throughout the City of Calgary called distrometers … meteorological tools that measure things like air pressure, precipitation … and an estimate of the size of the hail that hits it and the number of hits,” he said, adding they are typically placed at fire stations. Despite similarities in hail size to the 2024 storm, which caused more than $3 billion in insured losses, Woodward said this storm likely won’t have the same financial impact. “The Calgary event from last year was also a golf ball hail event and caused much more damage, but it was much more wind driven … and it lasted for quite a bit of time and hit some new neighbourhoods that were vulnerable to hail impacts.” The NHP’s findings are publicly accessible and aimed at informing everything from meteorology to building code revisions. “All our data is published through an open data portal. So yeah, we’re pure research. Anyone can use it,” said Woodward. ‘Frightening’ Homeowners in affected areas say the storm came suddenly and with a violent impact. “It was frightening, really,” said Frank Karas, a resident of the North Haven area. “It was like someone had a gun that was shooting at you, but we were all scared that it would break the window and the water would come in.” Karas said the volume of hail was “just insurmountable,”. The vinyl siding on his home is punched with holes while his neighbour’s stucco house received much less damage, suffering only broken window and paint scuffs. Those differences in damage are among the things the hail researchers are interested in studying. “We look at what breaks, what doesn’t, what materials are really good at standing up to hail and tornadoes, what materials are not,” said Woodward “Then we can recommend what materials people use in their houses, what goes in to building code reviews and how to improve resilience to these disasters into the future.” Quinn Vierling, who returned home from the Calgary Stampede to find his house had been struck, described a scene of downed trees and battered homes. “I was surprised that it was this bad, because Stampede grounds wasn’t hit that bad,” he said. “There’s trees down the street that are down and these trees are just totally shredded.” Vierling said this isn’t the first time he’s had to deal with hail damage. “Well, we had to get all our siding done, probably about 10 years ago from a big hail storm … Mother Nature is crazy.” The NHP team will remain in Calgary through at least Tuesday to continue its storm assessment.
