On March 26, 2011, about 0729 central daylight time, an Embraer EMB-145LR, N931AE, operated by American Eagle Airlines as flight 4355, sustained no damage when it encountered turbulence while in a climb north of Kansas City, Missouri, while en-route to the Chicago O'Hare International Airport (ORD), Chicago, Illinois. The 2 pilots and 49 passengers were uninjured. The flight attendant sustained a serious injury and the flight diverted to the Kansas City International Airport (MCI), near Kansas City, Missouri. The scheduled domestic passenger flight was conducted under the provisions of 14 Code of Federal Regulations Part 121. Visual meteorological conditions prevailed and an activated instrument flight rules flight plan was on file. The flight originated about 0705, from the Will Rogers World Airport (OKC), near Oklahoma City, Oklahoma. The operator reported that the flight attendant had finished her cabin service and was returning to her jumpseat when the airplane encountered convectively induced turbulence associated with a developing thunderstorm under the flight path while climbing through flight level (FL) 320. The flight attendant lost her footing and hit her head on the service galley door. While trying to find something to grab the flight attendant fell again and injured her wrist and knee. Immediately the flight attendant noticed her hand swelling up. She contacted the flight crew, informed them of what had happened, and stated to the crew that she would be unable to complete her duties. The flight crew elected to divert to MCI so the flight attendant could seek immediate medical attention. The flight attendant was met by paramedics and taken to the hospital. The operator subsequently confirmed that the flight attendant was seriously injured when her wrist and hand sustained fractures. The airplane’s flight data recorder data was reviewed. The data showed that the upset event occurred during the climb approximately 07:29:35. The data showed the vertical acceleration ranged from 1.54g to 0.60g in a 1-second period and that the airplane was climbing through FL 299. Review of the flight's dispatch records indicated scattered to broken areas of thunderstorms extending from eastern Oklahoma to western Arkansas with tops to 42,000 feet above sea level and it advised of possible convection over eastern Oklahoma. The dispatch paperwork did not include the latest convective significant meteorological information (SIGMET) 22C for an area of severe thunderstorms, which existed in the immediate vicinity of the upset location.