In parts of Chicago, flash flood alerts rang Tuesday, warning of dangerous conditions as cars were stranded and submerged on highways and water rescues were conducted, but how much rain actually fell across the region and how fast did it all happen?

More than a month's worth of rain fell on Chicago in 90 minutes on Tuesday evening, according to the National Weather Service (NWS). "There were numerous reports of flooded viaducts, several reports of water rescues, and a few reports of flooded basements," the NWS said.