THE NON-INSTRUMENT RATED 2800-HR PRIVATE PILOT WAS EXPERIENCED IN THE AIRPLANE AND FAMILIAR WITH THE ROUTE OF FLIGHT. THE PILOT OBSERVED THE DARK OVERCAST SKY CONDITIONS IN THE DIRECTION OF HIS PLANNED TRIP, & INDICATED THAT WHILE EN ROUTE IF THE WEATHER DETERIORATED HE WOULD RETURN TO THE DEPARTURE AIRPORT. THE PILOT TOOK OFF UNDER VFR CONDITIONS & HEADED IN AN EASTERLY DIRECTION. EIGHT MIN LATER THE PILOT CONTACTED RADAR & REQUESTED FLIGHT FOLLOWING SERVICE TOWARD HIS EASTERLY DESTINATION. TWO MIN LATER THE AIRPLANE WAS IDENTIFIED ON RADAR, & TWO MIN THEREAFTER RADAR CONTACT WAS LOST. THE LAST FOUR MIN OF RECORDED RADAR SHOWED THAT THE AIRPLANE HAD CLIMBED FROM 2600 FT TO 3500 FEET MSL & HAD TURNED 90 DEG LEFT FROM AN EASTERLY TO A NORTHERLY COURSE. NEARBY WEATHER REPORTING FACILITIES INDICATED THE CLOUD BASE & TOPS WERE RESPECTIVELY 3800 FT & 5700 FT MSL. THE CRASH SITE WAS 4750 FT MSL.