On December 18, 2019, at about 1109 EST, American Airlines flight 2247, an Embraer ERJ190, N959UW, encountered turbulence while enroute to Raleigh-Durham International Airport (KRDU), Morrisville, North Carolina. Of the 48 passengers and crew onboard, one flight attendant received a serious injury. The flight was operating under 14 Code of Federal Regulation Part 121 as a regularly scheduled domestic passenger flight from LaGuardia Airport (KLGA), Queens, New York, to KRDU. According to the flight crew, the flight was in cruise at flight level (FL) 200 with the seatbelt sign off because air traffic control had reported all pilot reports (PIREPs) as "smooth" and "no complaints". About one hour into the flight, they encountered a brief duration of "light to moderate chop" and illuminated the seatbelt sign. The flight crew requested a descent to FL180. The seatbelt sign was extinguished after the flight reached FL180 since the skies were clear, they were experiencing a smooth ride, and there were no pilot reports of turbulence. A short time later, the flight encountered "light to moderate chop" turbulence that lasted 20 seconds to a minute. The flight crew then received a call from the cabin advising them that a flight attendant (FA) had been injured. At the time of the second turbulence event, the FAs were conducting drink service in the cabin and the FA in the aft cabin was thrown to the floor, injuring her foot. One nonrevenue crew member described the turbulence encountered as “moderate to severe”. The injured FA was transferred to a passenger seat for the remainder of the flight. Upon being notified of the injury, the flight crew declared a medical emergency and requested paramedics meet the flight at the gate. After landing the FA was transported to a local hospital where she was diagnosed with a fractured foot. Post accident examination of the weather data determined that the airplane was passing through the lower boundary of a strong jet stream that was associated with significant shear. Moderate turbulence had been forecasted for the area of the encounter and there were no previous PIREPs of severe turbulence.