THE ACFT COLLIDED WITH A SIDE OF GLACIER PEAK AT ABOUT 10000 FT MSL WHILE IN LEVEL FLT. THE EXACT WEATHER CONDITIONS AT THE ACCIDENT SITE AT THE TIME OF THE ACCIDENT ARE UNKNOWN BUT SEVERAL MOUNTAIN CLIMBERS AT 6000 FT ABOUT 2 MILES AWAY ATABOUT THE SAME TIME DESCRIBE THE WEATHER AS SKY OBSCURED, VISIBILITY 50 FT IN LIGHT TO MODERATE WET SNOW, NO WIND. TEMPERATURE +38 DEGREES F. THE FLT WAS ENROUTE FROM ALDERWOOD MANOR TO THE PILOTS PRIVATE AIRSTRIP NEAR SPOKANE, WA. A WITNESS WHO HAD FLOWN THE ROUTE WITH THE PLT SEVERAL TIMES SAID THAT THE FLT NORMALLY PASSED SOUTH OF GLACIER PEAK AT ABOUT 10000-11000 FT. HE SAID THAT THE PILOT USED NAV AIDS ALONG THE ROUTE AND WOULD FLY IN CLOUDS IF THE WEATHER DICTATED IT. THE PILOT DID NOT NORMALLY TALK WITH ANYONE ON THE RADIO DURING FLT IN THE CLOUDS. HE DID HOWEVER ALWAYS GET A WEATHER BRIEFING. IT IS NOT KNOWN WHICH IF ANY NAV AIDS THE PLT USED DURING THE ACCIDENT FLT. THERE IS NO KNOWN RECORD OF COMMUNICATIONS BETWEEN THE ACFT AND ANY RADIO FACILITY.