Delta Airlines flight 1660, encountered turbulence at an altitude of FL 320 while enroute from Kansas City International Airport (MCI), Kansas City, Missouri, to Hartsfield–Jackson Atlanta International Airport (ATL), Atlanta, Georgia. One flight attendant (FA) sustained a serious injury, and the remaining crewmembers and passengers were uninjured. According to the captain, during the inbound leg to MCI, the flight encountered light turbulence. As a precaution, he instructed the FAs to complete the initial and final announcements simultaneously. That arrival was uneventful. For the outbound leg (MCI–ATL), the captain briefed the FAs to remain seated until he advised them it was safe to begin service. During climbout, the aircraft encountered light turbulence; however, upon reaching cruise altitude above a cloud deck, the flight was smooth. The flight crew reviewed the Flight Weather Viewer – a Delta proprietary app provided to their flight crews to use as a secondary source of weather, which indicated they were exiting the outer edge of an area of convection. No turbulence plots had been issued by Delta for the area, and other aircraft in the area also reported smooth conditions. The National Weather Service (NWS) Aviation Weather Center had issued a Convective Significant Meteorological Information (SIGMET) for an area of thunderstorms moving from 230° at 45 knots with tops to FL420 for the area. The advisory implied the potential for severe turbulence in and near the storms. After confirming smooth conditions, the captain advised the lead FA that cabin service could begin. About five minutes later, while in clear air, the airplane abruptly rolled about 15° to the right. The autopilot corrected the deviation, and the airplane experienced about 3 to 4 seconds of “moderate turbulence” before returning to smooth flight. The captain contacted the cabin to check on the FAs. One FA reported she had struck her head and shoulder but declined immediate medical assistance. The remainder of the flight continued uneventfully, and the airplane landed without further incident in Atlanta. After parking at the gate, the captain again confirmed the condition of the FA. The FA who struck her head stated she was communicating with inflight services and crew tracking regarding her next assignment. The captain provided his contact information for follow-up and reported the incident to the duty pilot. Meteorological reports provided by the airline indicated the flight likely encountered convective turbulence while overflying an area of convection which extended along the general route of flight. Delta issued a turbulence plot about 30 minutes later for the area.