The National Weather Service Chicago issued a Flash Flood Warning for southeastern Kane County that mentions Geneva and Batavia specifically as areas in the most danger.
According to the NWS-Chicago alert, the warning was aimed at central Cook County, DuPage County, northeastern Kendall County and southeastern Kane until 2 a.m. Monday. A dense fog advisory is also in effect until 8 a.m. Monday.
Trained weather spotters at 7:05 p.m. Sunday reported 2.6 inches of rainfall three miles southwest of North Aurora. Two inches of rain fell in the area between 5:30 p.m. and 7 p.m., according to the National Weather Service.
At 7:49 p.m. Sunday, Doppler radar indicated slow-moving thunderstorms with very heavy rainfall on the way. Several inches of water accumulated on Route 34 in Naperville.
At 8:10 p.m., a spotter reported 2.21 inches of rain and some street flooding two miles northeast of North Aurora.
"Runoff from this excessive rainfall will cause flash flooding to occur," the National Weather Service said.
Among the affected locations were Addison, Aurora, Naperville, Batavia, Bolingbrook, Burr Ridge, Downers Grove, DuPage Airport, Elmhurst, Geneva, Glen Ellyn, Hinsdale, Lemont, Lisle and Lombard.
"Be especially cautious at night when it is harder to recognize the dangers of flooding," the NWS says. "If flash flooding is observed, act quickly. Do not enter the water. Turn around and move up to higher ground to escape flood waters. Do not stay in areas subject to flooding when water begins rising."