What happened
Prior to takeoff, the flight crew received weather briefings that indicated potential thunderstorms and turbulence along the intended flight path. During the climb, as the aircraft passed through 24,000 feet, the crew diverted the flight around a rain shower that appeared benign.
As the aircraft passed the rain shower, it encountered three distinct jolts of moderate to severe turbulence. At the time of these encounters, all three flight attendants were in the process of preparing for cabin service. During the turbulence, one flight attendant sustained serious injuries.
Findings
According to the Continental Flight Manual, the flight crew is responsible for instructing the cabin crew to secure the cabin and remain seated prior to encountering turbulence.