Updated 7/23/11 4:05 p.m.

CHICAGO (STMW) – It’s officially the rainiest day since they began keeping records in 1871, according to the National Weather Service.

As of 10:30 a.m., 6.86 inches of rain has fallen since midnight, according to NWS Meteorologist Richard Castro.

“This is the rainiest calendar day already,’’ Castro said. “It’s an incredible amount of rain.’’

Nearly all of it pelted the area between the hours of 1 a.m. and 7 a.m., when 6.85 inches fell at O’Hare – the most since officials began keeping records in 1871.

The prior record was the 6.64 inches that fell on Sept. 13, 2008, Castro said.

Meanwhile, there is a possibly that more rain could fall later today, and temperatures are expected to be in the high 80s or 90.

“There is the potential for thunderstorms later today or tonight,’’ said Castro. Flash flood warnings are still in place for the entire metropolitan area, including Cook, Lake, McHenry, DuPage, Will and Kane counties and Lake County, Ind. until 1:30 p.m., Castro said.

The heavy rain downed “a lot of’’ electrical wires, causing multiple outages this morning, said ComEd spokesman Bennie Currie. High wind did not appear to be a problem, he said.

As of noon, there were still 74,000 ComEd customers waiting for their power to be restored, according to Currie. “The northern region is the hardest hit,’’ Currie said. There are 40,000 in that area. “No. 2 is the city and the near west suburbs, where 27,000 are without power,’’ Currie said.

The rest are 3,000 in the south and 4,000 in the west suburbs. Currie said more than 350 crews are in the field doing repairs and assessing the damage.

The heavy rains caused flooding on roads and expressways throughout the city, including Lake Shore Drive, police said.

On Interstate 57, the fire department rescued two semi truck drivers stranded on top of their trucks stuck in more than 10 feet of water near 99th Street, Fire Media Affairs Director Larry Langford said.

Initially, three truck drivers were stranded, but one decided to swim away through the murky water, Langford said. The semi and two tanker trucks remained on the side of the expressway ramp at 8 a.m.

The fire department brought the boat down I-57 and launched it like they would from a small craft ramp, Langford said.

Firefighters also rescued people stranded in flooded cars throughout the city – some sitting chest deep in water inside their vehicles, Langford said. Others were able to escape and waited on the roof of their vehicles until rescue crews arrived.

But as of 11:10 a.m. on the expressways in Cook County, “Everything is back to normal,’’ according to Illinois State Police District Chicago Master Sgt. Michael Merrill.

“Five minutes ago, we just opened the ramp from I-94 to I-57 north back up,’’ Merrill said. “That whole area was under water.’’ He said many cars were under water there, but no one was seriously injured.

You can go to the beach today, but no swimming because the rainfall brought with it bacteria, according to a release from the Chicago Park District. The Park District issued the swimming ban at all beaches until test results show low levels of bacteria in the water, the release said.

The Metropolitan Water Reclamation District (MWRD) opened the locks at Wilmette and the Chicago River downtown early this morning because of the heavy rains, the Park District release said.

Except for those taking the Blue Line to O’Hare Airport, things are looking better for most public transportation commuters, according to CTA spokeswoman Lambrini Lukidis.

As of 3:30 p.m., the Red Line and the Pink Line are both back to normal service.

Blue Line service was temporarily suspended between O’Hare and the Rosemont station, with bus shuttles transporting commuters. Later Saturday, reduced service continued on that last leg of the Blue Line on a single track.

The severe weather was not confined to the city.

Wheaton Police reported that a tornado touched down near the intersection of Butterfield Road and Route 83 in Oakbrook. Oakbrook Police could not immediately be reached for comment.

A tornado also reportedly touched down near the intersection of Grand Avenue and York Street in Bensenville about 2:45 a.m., Wheaton police said. However, Bensenville Police said they had no confirmed reports and that there was no noticeable damage.

At least one overnight fire may have been caused by a lightning strike overnight in the Lake View neighborhood on the North Side.

The blaze began shortly after 2 a.m. at a single-family home at 1617 W. Byron St., according to Langford.

One firefighter suffered a minor injury while battling the blaze, according to Langford, who said its cause may have been storm-related. “It might have been lightning,’’ said Langford of the cause.

While air travelers should still call ahead and leave extra time to get to and from the airports, things are looking better because of improving weather conditions, according to a release from the city’s Dept. of Aviation.

As of 3:30 p.m., because of the impact from overnight storms in the Chicago area, airlines at O’Hare International Airport are reporting only minor delays but cancellations remain at just over 100 flights, according to the CDA release.

Airlines at Midway International Airport are reporting normal operations.

Metra was reporting no problems because of the weather Saturday afternoon.

© Sun-Times Media Wire Chicago Sun-Times 2011. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.

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