A light turbulence event occurred during the climb after takeoff, with the seatbelt sign remaining illuminated. Subsequent turbulence was forecasted, leading to increased turbulence approximately 150 miles ahead. The captain instructed passengers to turn the seatbelt sign off for a 10-minute period to allow for movement, then turned it back on as predicted turbulence approached. During this time, two passengers fell as they attempted to sit down, and a flight attendant fell to the floor, fracturing her pelvis. The incident was likely caused by an encounter with the predicted turbulence during cruise flight.A light turbulence event occurred during the climb after takeoff, with the seatbelt sign remaining illuminated. Subsequent turbulence was forecasted, leading to increased turbulence approximately 150 miles ahead. The captain instructed passengers to turn the seatbelt sign off for a 10-minute period to allow for movement, then turned it back on as predicted turbulence approached. During this time, two passengers fell as they attempted to sit down, and a flight attendant fell to the floor, fracturing her pelvis. The incident was likely caused by an encounter with the predicted turbulence during cruise flight.