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A line of powerful thunderstorms rumbled across Dallas on Thursday, knocking out power for thousands and grounding flights — part of a system that stretched to the Great Lakes and threatened to bring flash floods, hail and perhaps even tornadoes.

Hundreds of thousands were without power across Texas late Thursday, including nearly 263,000 homes in the Dallas-Fort Worth area alone, according to Oncor Electric Delivery. Early Friday, the storms were heading towards Nashville.

Emergency management officials, already busy with the city’s response to the first U.S. diagnosis of Ebola, had to shift their attention. “Short break from Ebola Response to Severe Weather management,” Dallas emergency officials said on Twitter.

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Gusts as strong as 70 mph, almost the force of a tropical storm, were recorded as the storms tore through Dallas in the late afternoon, The Weather Channel reported. Police reported one minor injury after the roof was blown off a building at Arlington Baptist College, and a teacher in Denison was taken to the hospital after lightning either struck her or struck the ground next to her outside an elementary school, the county emergency management director said.

More than 700 flights into and out of Chicago were scrapped. It was mostly a precaution, but it complicated the travel mess created by a fire at a radar facility there last week.

People in Oklahoma, Missouri, Arkansas and Illinois were also warned to keep an eye out for storms. Around St. Louis, more than 6 inches of rain had already fallen in 24 hours. And in rural Jersey County, Illinois, 3½ feet of floodwater swept a car into a swollen creek, NBC affiliate KSDK reported. Rescuers pulled the driver to safety.

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Short break from Ebola Response to Severe Weather management pic.twitter.com/3kPabSb9sE — DallasOEM (@DallasOEM) October 2, 2014

— Erik Ortiz and Erin McClam