On August 16, 2003, about 1340 eastern daylight time, a Boeing 737-800, N329TZ, operated by American Trans Air Inc., as flight 820, was not damaged after it encountered turbulence during decent over Wooster, Ohio. There were no injuries to the 2 certificated airline transport pilots, 1 flight attendant, and 129 passengers; however, 1 flight attendant was seriously injured, and two additional flight attendants received minor injuries. Instrument meteorological conditions prevailed for the scheduled, international flight, which originated from the Cancun International Airport (MCUN), Cancun, Mexico, destined for the Cleveland-Hopkins International Airport (CLE), Cleveland, Ohio. Flight 820 was conducted on an instrument flight rules (IFR) flight plan under 14 CFR Part 121 According to a representative from the operator, the flight was being vectored around weather in the area of Cleveland, when it encountered turbulence. A flight attendant, who was preparing the cabin for landing, fell and suffered a broken ankle.