Hydrologic Outlook National Weather Service Chicago IL 443 AM CDT Sat May 12 2018 ...MULTIPLE ROUNDS OF HEAVY RAIN POSSIBLE TONIGHT AND AGAIN SUNDAY NIGHT... Multiple heavy rain producing thunderstorms may train over the same areas of northern Illinois tonight and again on Sunday night. Because of this, localized areas of northern Illinois could experience rainfall amounts in excess of 2 to 3 inches tonight, with additional heavy rainfall possible Sunday night. Because of this, there will be an increased threat of flash flooding, particularly if the heaviest rain producing storms train over the urbanized areas of Chicago and Rockford. This heavy rain will also likely result in significant rises and possible flooding on area streams and rivers. Stay tuned to the latest forecast information.