THE PLT OF AN SMA ACFT CONTINUED IN MVFR CONDITIONS TO THE DEST AFTER FLYING AN APCH INTO BFI AND CANCELING IFR. IN ORDER TO MAINTAIN VFR IN UNCTLED AIRSPACE; THE RPTR HAD TO FLY AT LESS THAN 1000 FT AGL OVER A CONGESTED AREA.

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IT WAS AN INST FLT FROM ELLENSBURG; WA; WITH A FINAL DEST OF AUBURN; WA. THE WX WAS BELOW THE MVA OF SEA APCH (2000 FT); SO I FILED FOR BFI. ALONG MY RTE OF FLT; I WAS IMC FROM 8000-2500 FT MSL WITH A SCATTERED LAYER BELOW AT 800-700 FT AGL. MY COMPANY TFC WAS APPROX 20 MINS AHEAD; LEAVING BFI ON AN SVFR CLRNC. I WAS MONITORING HIS PROGRESS TO AUBURN AND I HEARD HIM RPT THE FIELD IN SIGHT TO SEATTLE APCH; WHICH WAS THE SAME RTE I WAS ABOUT TO FLY. BFI'S ATIS WAS RPTING 700 FT SCATTERED; 1500 FT BROKEN; VISIBILITY 3 MI IN LIGHT RAIN AND FOG; AND AS I WAS CLRED FOR THE ILS RWY 13R AT BFI; SEA APCH WAS ADVISING SEA ATIS WAS 600 FT SCATTERED; 1500 FT BROKEN. KNOWING SEA IS 372 FT ABOVE AUBURN; I HAD ASSURANCE THAT I WOULD BE ABLE TO FLY THE TRANSITION TO AUBURN VFR AND CLR OF CLOUDS. AFTER COMPLETION OF THE APCH I WAS VFR BELOW 700 FT AGL WITH 1 MI VISIBILITY AND CLR OF CLOUDS. I CONTACTED SEA APCH FOR VFR FLT FOLLOWING TO AUBURN IN THE EVENT I WOULD NOT BE ABLE TO MAINTAIN 1 MI VISIBILITY AND CLR OF THE CLOUDS; I COULD HAVE PICKED UP AN IFR CLRNC TO BFI FOR THE ILS AND A FULL STOP. I FOLLOWED SR167 WHICH IS A 4 LANE HWY THAT LEADS TO THE APCH END OF RWY 16 AT AUBURN. ALONG MY CHOSEN RTE I ENCOUNTERED A RAGGED CEILING BTWN 700-500 FT AGL. IN ORDER TO MAINTAIN 1 MI VISIBILITY AND CLR OF CLOUDS; MY ALT WAS OCCASIONALLY 500 FT AGL WHICH PREVENTED ME FROM REMAINING 1000 FT ABOVE A CONGESTED AREA. AT ANY HIGHER OF AN ALT I WOULD HAVE BEEN IMC; SO I MADE THE DECISION TO REMAIN UNDER 700 FT AGL VFR TO AUBURN. THE FLT ENDED WITH A SAFE LNDG AT AUBURN BUT; TO AVOID FUTURE OCCURRENCES BELOW 1000 FT OVER A CONGESTED AREA; I WILL BE MAKING IFR APCHS TO A FULL STOP AND WAITING THE WX OUT; OR HAVE SOMEONE PICK ME UP AT ANOTHER ARPT WITH BETTER WX.