Southwest Airlines flight 4515, operating between Baltimore Washington International Airport (BWI), Baltimore, Maryland, and Orlando International Airport (MCO), Orlando, Florida, encountered moderate turbulence while in descent to MCO. One flight attendant sustained a serious injury and one sustained a minor injury during the turbulence encounter. The aircraft continued to MCO and landed without further incident. The captain served as the flying pilot and the first officer as the pilot monitoring for the entire flight. Prior to the flight, the crew reviewed the dispatch release and weather forecasts, which indicated areas of isolated rain showers storms to the east of the intended route. The flight crew stated that the takeoff, climb and cruise were normal, with occasional light turbulence. The flight crew stated that they had turned on the seatbelt sign earlier in the flight, and kept it illuminated as they began the descent into MCO. The first officer stated he had WSI Pilotbrief weather radar and SkyPath active on his electronic flight bag (EFB) and did not notice any turbulence being depicted for the descent to the airport. Air traffic control (ATC) indicated that there was rain on the arrival route, and recent pilot reports (PIREPs) indicated rides were smooth. The captain instructed the flight attendants to ready the cabin for arrival as the aircraft descended through flight level 190. As the flight continued the approach, air traffic control provided vectors to steer the flight clear of showers that were developing ahead. At about 14,000 feet, while passing through a cloud layer, the airplane encountered turbulence that lasted for approximately 11 seconds. Flight data recorder data indicated a maximum vertical acceleration of 2.30 g followed by a minimum of 0.59 g about 1.1 seconds later. During that same time, lateral acceleration also varied between -0.09 g to 0.14 g. The autopilot remained engaged during the entire event. A National Weather Service convective Significant Meteorological Information (SIGMET) was valid for the time of the event for areas east of the intended route. Tracking data and weather radar showed the flight traversed to the west of the SIGMET area, and the turbulence encounter occurred as the flight entered an area of precipitation that had a radar indicated echo top of 25,000 feet. There were no PIREPs of any turbulence in the immediate area at the time of the encounter. A PIREP of moderate turbulence near the encounter location was reported over an hour prior to the event, and light turbulence PIREPs in the area within an hour of the encounter were at altitudes above and below the altitude of the accident flight. At the time of the turbulence encounter the flight attendants (FA) were cleaning and preparing the cabin for landing. Two FAs were thrown into the air and then onto the floor. The FA in the aft galley sustained a serious injury to her ankle and the other FA was in the aisle and injured her hip. Emergency personnel met the airplane at the gate and transported both FAs to the hospital. One FA was treated and released and the other diagnosed with a fracture and dislocation of her right ankle.