"Words you don't want to hear: isolated flooding through city now," Mayor Naheed Nenshi said in a Twitter post. "We expect this will drain quickly when rain stops."
Low-lying areas such as Sunnyside, Mission and Victoria Park were back under water, submerging streets and sending water into basements once again.
Several major roadways were also affected, with reports of swamped cars being abandoned at some intersections, though the water quickly receded and many closed streets have since been reopened.
Secondary highways around High River, which is still struggling to recover from the June 20 flood, and Canmore were also closed due to high water.
The strain on people who had already been through one disaster was palpable on social media.
"Come on, Mother Nature," Tina Maker pleaded on Twitter. "Sunnyside in Calgary is under water again. Rain is coming down heavy."
"UGH!!" wrote Joanna Tzavaras, before adding a stream of expletives.
The city said this time the Bow and Elbow rivers were not to blame — the flooding was the result of already oversaturated soil and catch basins backing up.
However, officials said they were able to respond quickly as the city's emergency plan was still in effect and its emergency operations centre continues to be staffed.
Fire crews were dispatched to pump out flooded basements.
“Residents living in low-lying areas have been through a very difficult time these past two weeks and we are doing everything we can to address their concerns as quickly as possible,” Dan Limacher, director of water services, told a news conference Friday night.
The downpour also soaked the grounds of the Calgary Stampede, sending thousands of fairgoers and rodeo spectators scurrying for cover.
Weather forecasts indicate that additional rain is possible throughout the evening but by midnight it's anticipated the showers will become isolated.
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