What happened
While approaching South Bend, Indiana, an aircraft encountered moderate turbulence for several seconds as it climbed through FL200. Prior to this encounter, the flight crew had been utilizing radar to navigate around weather, and there were no prior pilot reports of turbulence. Additionally, the company dispatcher's weather package contained no warnings regarding turbulent conditions.
The turbulence was sudden and brief; the captain reported that the event started and ended so rapidly that there was insufficient time to alert the cabin crew. At the moment the aircraft encountered the turbulence, the seat belt sign was illuminated. During the disturbance, a flight attendant working in the aft galley fell to the floor, resulting in serious injuries to her back.