WHEN THE NON-INSTRUMENT RATED PLT DEPARTED FOR THE FLT AT ABOUT 2110 HRS, THE WX CONDITIONS WERE MARGINAL AND DETERIORATING IN THE AREA. NO RECORD OF A WX BRIEFING WAS FOUND. FOR UNKN REASONS, THE PLT WAS RETURNING TO THE ARPT AFTER ABOUT 1 HR AND 20 MNS, ENTERED THE BANNING PASS FROM THE EAST AND ENCOUNTERED CEILINGS OF APRX 500 FT AGL AND VISIBILITIES OF 1 MI OR LESS IN FOG AND DRIZZLE. BY THE TIME THE PLT CONTACTED THE NORTON AFB ATCT, HE WAS UNABLE TO CLEARLY LOCATE HIS POSITION IN THE DARKNESS AND RESTRICTED VISIBILITIES. THE RADIO TRANSMISSION FROM THE PLT, 'WE'RE HAVING PROBLEMS GETTING IN VFR WE'RE GOING TO TRY TO CLIMB AND GET ABOVE THIS (WEATHER)' ESTABLISHED HIS INTENTION TO TRY AN INSTRUMENT CLIMB THROUGH THE CLOUDS TO FIND VFR CONDITIONS. THE WITNESSES OBSERVED THE ACFT ENTER THE BASE OF THE CLOUDS THEN DESCEND 'STRAIGHT DOWN OUT OF THE CLOUDS.' THE PHYSICAL EVIDENCE AT THE SITE ESTABLISHED THAT THE ACFT CONTACTED THE GROUND IN AN ATTITUDE CONSISTANT WITH A RIGHT SPIN.