On April 7, 1997, about 0800 eastern daylight time, an Airbus A320-232, N413UA, operated by United Airlines as flight 203, encountered turbulence during cruise flight. Five crew members and 39 passengers were not injured, and 1 flight attendant received serious injuries. The airplane was not damaged. The flight had departed the General Edward Lawrence Logan International Airport (BOS), Boston, Massachusetts, about 0725, destined for Newark International Airport (EWR), Newark, New Jersey. An instrument flight rules flight plan had been filed for the scheduled domestic flight conducted under 14 CFR Part 121. According to a United Airlines representative, the pilot obtained a company generated full weather briefing which did not call for turbulence for the route of flight. The flight was routed to EWR via BOS, GLYDE intersection, V292, V213, SAX, EWR, at 16,000 feet. While en route, during cruise, the flight encountered unexpected and unforecasted turbulence. A flight attendant working with trays in the aft cabin fell, and fractured a bone in her foot. The weather at BOS at 0656 and 0756 respectively reported winds from 220 degrees at 8 knots; visibility 2 1/2 miles with fog; ceiling 400 broken; 600 overcast; temperature and dew point 55 degrees Fahrenheit; altimeter 29.68" Hg; and winds from 230 degrees at 8 knots; visibility 3 miles with fog; 400 scattered; 600 scattered; ceiling 1200 overcast; temperature 56 degrees Fahrenheit; dewpoint 55 degrees Fahrenheit; altimeter 29.70" Hg.