On April 12, 1999, about 1110 eastern daylight time, an American AA-5, N8764J, was substantially damage after entering instrument meteorological conditions (IMC), and impacting a tree in the vicinity of Stiefler Corner, Pennsylvania. The certificated commercial pilot and passenger were not injured. Visual meteorological conditions (VMC) prevailed for the personal flight that originated from Shenandoah Valley Regional Airport (SHD), Staunton, Virginia, about 1030, destined for St. Marys Muni Airport (OYM), St. Mary's, Pennsylvania. No flight plan was filed, and the flight was conducted under 14 CFR Part 91. The pilot and his son were conducting a cross country flight from Sebastian, Florida, to their home in New York State, when the accident occurred. They departed Sebastian the day before the accident and proceeded to Shenandoah, via Saint Agustine, Florida and Walterboro, South Carolina. After reaching Shenandoah the day before the accident, about 1600, the pilot checked weather on a computer terminal in a FBO. Because of wide spread IFR conditions across the northeast, he decided to postpone his departure until the next day. The pilot added that he was instrument rated, and the airplane was legal for IFR flight, but since he had not planned on conducting IFR operations on this trip, and because of his limited IFR experience, he would only conduct VFR operations. On the day of the accident, the pilot arrived at the airport, about 0945. He checked the forecast, and current weather radar for his intended route of flight. According to the pilot, the lowest ceiling forecasted for the route was 1,500 feet in the Pennsylvania area. After the pilot preflighted the airplane, he taxied it onto runway 23, and started to initialize his GPS. While the accident airplane was on the runway, a landing airplane called a 4 mile final for runway 5 at Shenandoah. The accident pilot expedited his departure, and forgot to complete the GPS initialization. Approximately 1 1/2 miles to the east of Shenandoah, the pilot realized he had forgotten to initialize the GPS. He then completed the initialization using runway 23's position. South of New Cumberland, West Virginia, the pilot encountered moderate turbulence for about 3 minutes. During the encounter, he reduced the airplane's airspeed to "maximum turbulence penetration speed". Also at this point, he estimated the flight conditions to be 3,500 overcast, and 10 miles of visibility. The airplane entered a second area of turbulence between New Cumberland and Altoona, Pennsylvania. At this point, the airplane was approximately 3,000 feet msl and the valley floor was about 1,250 feet msl. Mountain tops on both sides of the valley were obscured by clouds, but flight visibility was still 10 miles. As the airplane progressed up the valley, the ceiling continued to lower, but the pilot maintained altitude fearing sever turbulence closer to the valley floor. Then while operating the airplane less then 500 feet from the base of the clouds, and approximately 2,000 feet agl, the pilot focused his attention inside the cockpit to tune radio's and confirm his positions using a map. He was concerned about the accuracy of his GPS position because he did not initialize it on the ground. During this period, the pilot speculated that he let the airplane climb into the overcast. "I was not paying attention and I was close to the base of the clouds." The airplane entered the clouds and the severity of the turbulence increased. The pilot knew the airplane was close to terrain, so he initiated a climb, and started a left turn to proceed back to the south in an attempt to regain VMC, but during the turn, and approximately 3,200 feet msl, the airplane struck a pine tree about 6 feet below its top. The pilot continued the climbing left turn, set the transponder to 7700, and transmitted a "May Day" call on 121.5. He included in his May Day that he was inadvertent IMC, in icing conditions, and experiencing moderate to sever turbulence. An airline pilot acknowledged the May Day, and suggested carburetor heat to the pilot who then selected carburetor heat on. About 5 minutes later, the pilot regained VMC, and landed the airplane at Bedford, Pennsylvania, without further incident. The pilot added that after impacting the tree, the airplane's flight characteristic did not change, and that he noticed no change in engine performance. He also stated that, "I was less then 500 feet below the base of the clouds prior to going IMC." He contributed his close proximity to the clouds, diverting his attention inside the cockpit to tune the radios, and examining the map for an extended period as factors in the accident.