THE PILOT HELD A PRIVATE PILOT CERTIFICATE WITH NO INSTRUMENT RATING. HE FILED A VFR FLIGHT PLAN. OFFICIAL WEATHER OBSERVATION REFLECTED THUNDERSTORM ACTIVITY ALONG THE PROPOSED ROUTE OF FLIGHT. THE AIRCRAFT ENTERED AN AREA OF INTENSE THUNDERSTORM ACTIVITY. WITNESSES OBSERVED THE ACCIDENT AIRCRAFT DESCENDING MINUS A LARGE SECTION OF ONE WING AND IMPACTING THE GROUND IN MOUNTAINOUS TERRAIN.