* WHAT...Flash flooding caused by excessive rainfall continues to be possible. * WHERE...Portions of Illinois, including the following areas, Bond IL, Calhoun IL, Clinton IL, Fayette IL, Greene IL, Jersey IL, Macoupin IL, Madison IL, Marion IL, Monroe IL, Montgomery IL, Pike IL, Randolph IL, Saint Clair IL and Washington IL and Missouri, including the following areas, Audrain MO, Boone MO, Callaway MO, Cole MO, Crawford MO, Franklin MO, Gasconade MO, Iron MO, Jefferson MO, Lincoln MO, Madison MO, Moniteau MO, Montgomery MO, Osage MO, Pike MO, Reynolds MO, Saint Charles MO, Saint Francois MO, Saint Louis City MO, Saint Louis MO, Sainte Genevieve MO, Warren MO and Washington MO. * WHEN...Through Friday evening. * IMPACTS...Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. * ADDITIONAL DETAILS... - Multiple waves of thunderstorms capable of heavy rainfall. - Some locations that may experience flooding include... St. Louis, Columbia, O'Fallon, St. Charles, St. Peters, Florissant, Chesterfield, Belleville, Jefferson City, Wildwood, University City, Ballwin, Granite City, Wentzville, Alton, Kirkwood, Maryland Heights, East St. Louis and Hazelwood.