The warning affected a narrow, but densely populated area that included downtown Chicago. Flash flooding was seen from the downtown area through the West Side along the Eisenhower Expressway to Oak Park, as the slow-moving storm hovered stubbornly over the area.

The much-awaited preliminary report on the devastating Air India crash, involving a Boeing Co. BA +1.68% Get Free Report airplane, in June, which claimed 260 lives, is expected to be released by the end of this week.

A preliminary report into the deadly crash of an Air India jetliner in June is expected to be released by Friday, three sources with knowledge of the matter said, with one adding the probe had narrowed its focus to the movement of the plane's fuel control switches.