Weekend thunderstorms wreaked havoc Sunday across Chicago, resulting in flooding the National Weather Service described as “potentially life-threatening,” swamping highways, halting some Chicago Transit Authority services and damaging dozens of homes. A flash flood warning is in effect until 3:15 p.m.

More than 250 residents had submitted basement flooding complaints to 311 since Saturday afternoon when the National Weather Service began issuing storm warnings. The vast majority stem from Austin.

Neighborhood resident Shirley Howard said she checked her basement Sunday morning after hearing a neighbor’s home had flooded. “I came downstairs and the water met me at the second step,” Howard said, in standing water up to her ankles. “I don’t think I’ll be able to save anything.”

Torrential rains put a damper on the first NASCAR Chicago Street Race as standing water covered parts of the course and fans waited in the rain for the races to resume. NASCAR officials declared Cole Custer the winner of the Xfinity Series Race on Sunday after lightning forced officials to shut it down Saturday with just under half the laps completed. The main event — NASCAR Cup Series Grant Park 220 — is scheduled to start at 4:05 p.m.

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The flooding also created chaos for Sunday travelers, closing portions of two major interstates — on I-290, east of Des Plaines and I-55 east of Pulaski. The weather service encouraged travelers to “strongly consider” avoiding nonessential travel until the rain eases and water recedes.

Amid multiple CTA bus delays — and the suspension of portions of Blue and Pink line service — the agency encouraged affected commuters to consider alternative transit routes. Service was indefinitely suspended, as of 10:30 a.m., on the Blue line between Harlem and Forest Park, and on the Pink line between Pulaski and 54th/Cermak, due to track conditions. The CTA said shuttle buses will provide connecting service in those areas.

Following Saturday storms, 3 to 5 inches of rain fell in some areas Sunday morning, with the continued torrential rainfall also causing flooding in nearby suburbs, according to the weather service.

Whether the weekend’s storms improved drought conditions is yet to be determined, NWS meteorologist Casey Sullivan told the Tribune. “A lot of rain in the city today ran off because it came down so hard and ran into creeks and streams and then reservoirs,” he said.

“You need a gentle, light to moderate rain that allows it to soak into the ground. It certainly helped in the immediate short-term, but in terms of long-term drought improvement, it remains to be seen,” Sullivan said, noting that any positive effects may also be hyperlocal, with variation in the amount of rainfall across Chicago.

Rain can potentially improve air quality by clearing out particle pollutants in the atmosphere. “However, the Canadian wildfires where the smoke originated from are still burning,” Sullivan said. “Could we get more smoke later this week or next week or the following week — it’s a possibility.”

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Because of climate change, scientists project that Chicago will see an increase in extreme precipitation events, with long dry spells between them, according to the Metropolitan Mayors Caucus Climate Action Plan for the Chicago region.

The change in weather patterns will increase the frequency and intensity of both flooding and drought, scientists project, noting that the impact won’t be felt equally. “Communities with lower incomes and a high proportion of minority residents typically have the greatest exposure to flooding,” the plan states. “Due to historical disinvestment, these same communities also tend to have lower capacity to prepare for and recover from flood events.”

As the president of her block club in Austin, a predominantly Black community home to nearly 100,000 residents, Howard said neighborhood homes repeatedly flood. “It’s starting all over again. Everything’s got to be stripped, cleaned,” she said of the home, near Lockwood and Chicago avenues, where she’s lived for nearly 30 years. “They just need to get a better system.”

Efforts to reach Ald. Emma Mitts of the 37th ward, where Howard lives, were unsuccessful. Ward residents filed a quarter of all basement flooding complaints filed over the weekend as of 2 p.m. Sunday.