Unusual thunderstorm floods parts of Calgary, dumps up to 70 mm of rain

An unusual thunderstorm Thursday evening flooded parts of Calgary, dumping up to 70 millimetres of rain in areas.

The weather stranded vehicles in water, closed intersections, backlogged traffic, delayed flights and sparked power outages.

Hail sprinkled parts of the city and people captured pictures of lightning strikes. Heavy winds may have contributed to a thousands of customers losing power.

It rained most of the day but around 8 p.m., a long and narrow thunderstorm formed, said Kyle Fougère, a meteorologist with Environment and Climate Change Canada. The storm crossed the city from the northwest to the south over downtown.

The end of June and early July is Calgary's "busy thunderstorm season," but Fougère called this storm "rare" because of its unusual shape, focusing the rainfall in a specific area.

"It's not typical for it to dump that much precipitation right over a heavily populated centre," Fougère said.

"And when it falls over a place like Calgary that has so much infrastructure and so much asphalt and concrete and things that don't absorb precipitation, that's when you have these flooding events."

Most Calgarians would have seen between 20 and 30 millimetres at least, he said. Others saw as much as 50 to 70 millimetres.

One data collection site reported a whopping 74.4 mm, the bulk of which fell within an hour and a half.

"So it wasn't unique for this time of year and it wasn't unique for the thunderstorms — but it was unique to have such a narrow line right over top of the city," Fougère said.

The flash floods caused traffic issues and kept police busy throughout the evening.

The Calgary Police Service warned people to stay off the roads if they didn't have to be out. They urged drivers to be careful going through puddles as some were deep enough to bog down cars.

In downtown Calgary, a group of young men found their car swamped when water pooled in the Eighth Street S.W. underpass. Leaving their car, they were soaked, and police had to block off the road where their vehicle stalled, even after the water subsided.

A massive puddle blocked one of three lanes on Macleod Trail at 58th Avenue S.E. in the intersection, with drivers reporting that a sinkhole had been developing. Police parked at each end to turn back a steady stream of vehicles.

Police also reported flash flooding in the following locations:

• Southland Drive S.E. and Acadia Drive 
• 60th Avenue S.E. and Fifth Street
• 36th Avenue N.W. and Fourth Street
• Fourth Street N.W. and 40th Avenue
• Eighth Street S.W. and 10th Avenue
• Ninth Avenue S.E. and First Street
• Southbound Macleod Trail at Ninth Avenue

Between 8 p.m. and midnight, officers received 29 calls related to issues such as vehicles affected by water, street issues in neighbourhoods and vehicles in standing water.

About 21,000 customers lost power between 8:30 and 11:30 p.m., a spokesperson for Enmax said.

CBC readers reported manhole covers being blown off, and one described Heritage Drive and Macleod Trail as turning into "a small lake" that thankfully drained quickly.

Others posted pictures and videos of water rising above their ankles or halfway up their vehicle wheels.

The Calgary International Airport reported the thunderstorms delayed flights.

The city saw a lot of rainfall earlier this month, as well. The weather data station at the airport measured nearly 54 millimetres on June 21. Rainfall that day prompted warnings in southern Alberta and a flood alert in nearby Airdrie.

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More rain is forecast for Saturday in Calgary. Sunday's weather is expected to be sunny with a high of 22 C.

Canada Day celebration attendees should bring an umbrella. Environment Canada is predicting a 60 per cent chance of showers.