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.

Investigators have hinted that pilot error will likely be deemed the cause of the disaster, with a focus on the engine fuel control switches.

A preliminary report into the deadly crash of an Air India jetliner in June is expected to be released tomorrow, 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.