DURING HIS WEATHER BRIEFING THE PILOT WAS ADVISED THAT VFR FLIGHT WAS NOT RECOMMENDED DUE TO CLOUDS OBSCURING THE MOUNTAINS AND/OR PRECIPITATION ALONG THE ENTIRE ROUTE. WITNESSES SKIING ABOUT 3/4 MI FROM THE ACCIDENT SITE REPORTED HEARING AIRPLANE ENGINE SOUNDS OVERHEAD; THE AIRPLANE WAS NOT OBSERVED DUE TO LOW CLOUDS AND SNOW FLURRIES. THE ENGINE SOUND ABRUPTLY ENDED WITH A METALLIC THUD. THE AIRPLANE HAD IMPACTED 33 DEG UPSLOPING TERRAIN AT ABOUT 8.600 FT MSL.