The non-instrument rated pilot told witnesses that he would attempt to cross mountains north of the departure airport where he expected to find clear weather before he proceeded west toward his destination. A witness said the weather at the departure airport was about 1200 overcast with good visibility below the overcast. The pilot had flown about 35 miles and was over the Blue Ridge Mountains, when according to recorded radar data, the aircraft began to change course about 14 times, including several course reversals, during about a 15 minute period. During this time the aircraft climbed from 2100 to 7200 feet. A witness near the accident site said it was raining, visibility 1000 feet, and the mountain tops were obscured by clouds when he heard the aircraft at full power and climbing shortly before he heard a 'muffled' sound followed by silence. The aircraft experienced an inflight breakup consisting of separated portions of the right wing and right horizontal stabilizer. Examination of the wreckage did not reveal evidence of mechanical malfunction.