According to crew statements, the flight encountered light turbulence while deviating around areas of weather depicted on the onboard weather radar during descent from FL350 to 12,000 feet. Air Traffic Control (ATC) had also advised them of areas of precipitation shown on ATC radar. The seatbelt sign was turned on and the flight crew advised the cabin crew to complete service and be seated for arrival. The flight was returning on course after it appeared they were clear of significant weather when they encountered an area of moderate turbulence and briefly encountered what the crew characterized as severe turbulence. A flight attendant (FA) in the aft galley was lifted into the air and fell back down to the floor injuring her ankle. The flight crew was notified of the injury and they requested paramedics meet the airplane upon arrival. The FA was transported to the hospital where she was diagnosed with a fractured ankle. Probable Cause: An inadvertent encounter with convective turbulence resulting in serious injury to a flight attendant.