A tornado warning has been issued for part of the Chicago area Saturday afternoon with golf ball-sized hail possible, according to the National Weather Service.
The warning was issued for Livingston County until 2:15 p.m.
"This storm that is straddling Livingston and McLean counties has been showing increasing low-level rotation, and appears capable of producing a tornado at any moment," meteorologists said in a tweet.
The National Weather Service earlier announced a severe thunderstorm warning for Kane, Kendall and DeKalb counties until noon and for DuPage and Will until 11:15 a.m.
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Saturday morning, portions of Cook and Will counties were 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.
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.
A tornado also 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.
High winds and heavy rainfall were the primary threats of the initial 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.