The City of Calgary was slammed with two massive thunderstorms Tuesday evening, causing power outages, splintered trees, sewer blockages and even a flyaway roof.
“There is a lot of rain that came down with this storm,” said Dave Carlsen, a meteorologist with Environment Canada.
“Radar estimates that right over the downtown, somewhere between 80 mm to 90 mm fell within an hour.”
That’s far more than the monthly average for August in Calgary, which normally receives 40 to 60 mm for the entire month.
Environment Canada issued the first severe thunderstorm warning for the city just after 4:30 p.m. and the second at about 5:30 p.m.
“One storm went through the city — and went pretty much right through the middle — and then another storm decided to start on its heels and move through the south end of town,” said Carlsen.
Enormous sheets of rain swept across the downtown, obscuring the skyline building-by-building until visibility was zero.
Hail the size of toonies broke windows, vehicles were flooded and trapped in underpasses, heavy winds ripped the roof off of a northeast residential complex and manhole covers were blown off of their foundations, said Sue Henry, deputy chief of Calgary’s Emergency Management Agency (CEMA).
She said 911 experienced a flood of calls: For an half-hour period around 4:30 p.m., 246 calls were answered.
“This is six-times the average call volume that they receive at this time and fortunately it occurred during a shift change that allowed 911 staff that were oncoming and off-going to be able to answer calls,” she said. And between 4:30p and 7 p.m. calls into 911 resulted in 440 dispatches of emergency crews.
City workers were also called on to tend to broken trees and blocked catch basins said Henry.
And power outages left many residents and traffic lights without power.
Environment Canada says August thunderstorms are typical for Calgary.
“You tend to get a lot of thunderstorms that form just on the east side of the Foothills of the Rockies,” said Carlsen.
“They form all the way from the B.C. Peace Country all the way down to Colorado, just about everyday.”
However, these storms are typically small with little rain, hail and wind, he said.
“But when you get a strong trough in the upper atmosphere … (and) when you get those coming through, they help to make the thunderstorms stronger and that’s what happened,” he said.
Calgarians are in for more stormy weather this week.
There’s another chance of severe thunderstorms in the southern end of the province Wednesday.
“Right now we think that the biggest threat is south and east of Calgary but that could change,” said Carlsen.
For Thursday there is a 70% chance of showers and more thunderstorms are expected through the weekend.