A tornado likely touched down in south Naperville early Saturday morning, according to data from the National Weather Service.
An initial storm survey showed a tornado in the west suburb based on observed damage and a downstream tornadic debris signature on the radar, meteorologists say.
The approximate starting point was at a shopping plaza on the northeast corner of Route 59 and 95th Street, though an assessment is still ongoing.
Saturday morning, portions of Cook and Will counties are experiencing flooded roadways and viaducts after storms swept through the area, bringing heavy rainfall and damaging wind gusts of up to 60 mph, triggering tornado warnings for the two counties.
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As of just after 6 a.m. Saturday, a severe thunderstorm warning remained in effect for Cook, Will and southern portions of DuPage counties after the tornado warnings expired. By 7 a.m., the storm moved into northwest Indiana, and many Chicago-area counties were under a flood watch.
High winds and heavy rainfall were the primary threats of the storm, and nearly 150 homes were without power as of Saturday morning.
"The tornado threat has eased, though still severe winds (60+ mph) moving through parts of Illinois along/east of I-57 and into northwest Indiana," the National Weather Service tweeted. "The message ahead of these storms remains largely similar -- get inside, away from windows."
Flooding was reported across the area, from underpasses in Oak Park to roadways in Hoffman Estates. Flooding also was reported on the Eisenhower Expressway, slowing traffic as cars eased through the water.
The threat for storms is expected to diminish across the area later Saturday morning and into the afternoon, but but chances for severe weather are possible again Saturday night into Sunday. High winds and heavy rain are again considered main threats, with the possibility of a tornado.
Conditions could be hot in the daytime Saturday, as 91-degree temperatures are possible.