On August 20, 2001, about 0104 Pacific daylight time, an Airbus A320-232, N605AW, operated by America West Airlines as flight 579, while on a Title 14 CFR Part 121 scheduled domestic flight, encountered moderate turbulence associated with convective activity while climbing through flight level 250 near Needles, California, and continued on to Tampa, Florida. Visual meteorological conditions prevailed. An IFR flight plan was filed. The airplane was not damaged. The flightcrew of two, two flight attendants, and 135 passengers reported no injuries. One flight attendant reported serious injuries. The flight had departed Las Vegas, Nevada, at 0045, was destined for Tampa, Florida, and landed there at 0501 (0801 eastern daylight time). The flight was assigned a routing over Needles and Buckeye, Arizona, to avoid thunderstorm activity. The seatbelt sign was illuminated. The flight encountered moderate turbulence for approximately 5 seconds. One flight attendant, who was standing in the aft galley, struck her head and was knocked unconscious for approximately 5 minutes. The flightcrew communicated with the dispatcher, a medical advisory firm, and an onboard physician and the determination was made to continue to the destination. The flight attendant was unable to perform further duties. Upon arrival, the injured flight attendant was transported to the hospital for observation, where she remained for 48 hours. At the time of the accident convective SIGMET (Significant Meteorological Advisory) 12W was valid until 0655, for Arizona (AZ), Utah (UT), and Nevada (NV), and covered the area from 50 miles west of Bryce Canyon, UT, to 20 miles south of Peach Springs, AZ, to 30 miles east of Las Vegas, NV, to 50 miles south of Wilson Creek, NV, and back to 50 miles west of Bryce Canyon, UT. The SIGMET stated: "..…AREA TS MOV LTL. TOPS ABV FL450." Area of thunderstorms moving very little. Top above 45,000 feet mean sea level.