The rainfall that put much of the suburbs underwater Thursday fell far short of the worst we've seen in terms of inches, but experts say the result was reminiscent of a record-breaking downpour that nailed the suburbs -- and especially the Aurora-Naperville area -- in 1996.
"The magnitude wasn't as big but, because the ground is saturated, we're seeing pretty significant impacts," said meteorologist Jim Allsopp of the National Weather Service in Romeoville. "They're pretty similar in a lot of respects."
Allsopp said the South suburbs had received between 6 and 7 inches of rain as of Thursday morning, with another 1 to 2 inches forecast. To the north and west, about a quarter- to half-inch more was expected.
That's roughly half of what fell on parts of Aurora in July 1996, when the city set a state record with nearly 17 inches in 24 hours. Naperville received 14 inches, and 13 northern Illinois counties were declared disaster areas by Gov. Jim Edgar.
Even with less rain, Thursday's floods were comparable because of ground saturation and spring conditions.
"It's been raining all month, so the streams and rivers were already at or near flood stage," Allsopp said. "There's really no place for the water to go, whereas in July you're typically pretty warm and a lot of the water will evaporate out of the ground. The ground can take more of it in that situation rather than the situation we have now."
It was a more enduring rain in September 1986 that caused one of the most severe Des Plaines River floods on record.
That year, waves of storms hammered southern Wisconsin and northern Illinois for two weeks, with some areas getting 13 inches, according to Daily Herald archives.
Another flood the following year, in August 1987, didn't help matters.
More than 9 inches of rain fell in 18 hours at O'Hare International Airport and left communities ravaged along Salt Creek, a heavily developed Des Plaines River tributary through northwest Cook County and DuPage County.
Those two floods combined caused more than $100 million in damage to the Chicago region and set the stage for lawmakers to enact the state flood-control framework that remains in place today.
In September 2008, more than 6 inches of rain fell at O'Hare, causing the Des Plaines River to rise at least 4 feet higher than the flood stage of 5 feet. At the time, officials said the effect on the river was similar but not as bad as the 1986 flood.