An aircraft encountered moderate turbulence approximately one second in duration, involving a broken layer of clouds and a 2,000-foot vertical buildup. The flight crew prepared for landing six minutes prior to the turbulence. Radar and visual observations indicated minimal more than light turbulence. A flight attendant reported the captain’s statement of potential turbulence ahead, prompting a cleanup procedure. A flight attendant fell onto the seatback, requiring assistance, and subsequently broke an ankle. Emergency personnel responded, providing a splint and transporting the flight attendant to the hospital, where the ankle was discovered to be broken. The probable cause is the turbulence resulting in injuries to the flight attendant.An aircraft encountered moderate turbulence approximately one second in duration, involving a broken layer of clouds and a 2,000-foot vertical buildup. The flight crew prepared for landing six minutes prior to the turbulence. Radar and visual observations indicated minimal more than light turbulence. A flight attendant reported the captain’s statement of potential turbulence ahead, prompting a cleanup procedure. A flight attendant fell onto the seatback, requiring assistance, and subsequently broke an ankle. Emergency personnel responded, providing a splint and transporting the flight attendant to the hospital, where the ankle was discovered to be broken. The probable cause is the turbulence resulting in injuries to the flight attendant.