The aircraft was flying in an area of thunderstorms with the nearest cell 40 miles to the left of course. The captain said the top of a thunderstorm cell was “not painting on radar.” They had been expecting light chop but encountered moderate turbulence instead. When the airplane encountered the turbulence, a flight attendant struck the ceiling and a beverage cart. The seat belt light was illuminated at the time. An emergency was declared and the aircraft landed at Denver without further incident. The injured flight attendant was taken to a hospital. An AIRMET for “occasional moderate turbulence between FL270 and FL400 associated with jet stream windshear” had been in effect for the area. There were no PIREPS (pilot reports) of turbulence before the accident, but in the 40 minutes after the accident, there were 5 pilot reports of moderate turbulence at altitudes between FL320 and FL380. Probable Cause: the inflight encounter with moderate turbulence.