A CPR SMT FLEW INTO A FOG LAYER AFTER TKOF AT NIGHT.

Narrative

THIS WAS AN IFR (VFR ON TOP) FLT FROM PORT ANGELES TO HOQUIAM; WA. PORT ANGELES WAS CLR WHEN I WENT TO THE ARPT. IT TOOK A LITTLE WHILE (PERHAPS 45 MIN) TO GET UNDERWAY. I HAD AN ALTERNATOR PROBLEM AND DECIDED TO DEPART THE FIELD VFR AND PICK UP MY IFR CLRNC ENRTE FROM WHIDBEY AFTER SORTING OUT THE PROBLEM. ONCE AIRBORNE FROM RWY 8 THE ACFT ENTERED A THIN LAYER (500 FT) OF FOG JUST E OF THE ARPT. I TURNED L (THE DA 1 DEP) AND CALLED WHIDBEY. THEY MENTIONED AN INBOUND ACFT AT 1100 FT (WHEN I WAS AT 1800 FT) INBOUND ABOUT 2 MI AWAY ON A 'SPECIAL' INTO PORT ANGELES. I WAS QUICKLY VFR AND RECEIVED MY CLRNC TO HQM. THIS WAS AN UNEXPECTED ENTRANCE TO IMC WHICH WAS QUITE SURPRISING SINCE THE FIELD WAS QUITE CLR (STARS OUT; ETC) BUT APPARENTLY; WITHOUT MY KNOWLEDGE; IT HAD BEEN DECLARED IMC BECAUSE OF THE FOG LAYER WHICH HAD MOVED IN. MY DEP INTENTIONS HAD BEEN ANNOUNCED ON UNICOM BUT AT THAT TIME; THERE WAS NO MENTION OF OTHER ACFT OR IMC CONDITIONS. IT WOULD BE QUITE HELPFUL IF UNICOM PERSONNEL WOULD ADVISE PLTS OF IMC CONDITIONS; PARTICULARLY IF THEY ARE NOT APPARENT.