PLT OF A BE33C ENCOUNTERS DETERIORATING WX AND SIGHTS AN ACR BELOW HIM. HE DSNDS INTO CLR WX THEN FLIES IFR FLT PLAN.

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I WAS ON A VFR FLT BTWN 2 BROKEN/OVCST LAYERS AT 6500 FT. THE INFLT VISIBILITY AND CLOUD CLRNCS DEGRADED TO THE POINT I WASN'T SURE IF I STILL MET THE 3 MI 500/1000/2000 VFR VISIBILITY AND CLOUD CLRNCS. I WAS RECEIVING TA'S FROM APCH CTL. AT ONE POINT; A COMMERCIAL JET PASSED ABOUT 1000 FT BELOW AND 1000 FT BEHIND US. (APCH DID NOT CALL OUT THE TFC.) I DIVERTED TO A CLRER AREA TO THE N AND DSNDED VFR BELOW THE BROKEN LAYER. I PICKED UP AN IFR CLRNC AND CONTINUED TO THE DEST. I MADE THE WRONG DECISION IN CONTINUING INTO MARGINAL CONDITIONS IN THE EXPECTATION THAT THE CLOUD SIT WOULD IMPROVE BASED ON THE BRIEFING FORECAST AND ATIS RPTS AHEAD OF ME. I COULD JUST AS EASILY HAVE PICKED UP AN IFR CLRNC EARLIER; WHEN IT WAS APPARENT THE WX WAS BECOMING MARGINAL. I REMAINED CLR OF CLOUDS; BUT DO NOT KNOW IF I MAINTAINED VFR VISIBILITY AND CLOUD CLRNCS. IF THE JET PASSING BELOW HAD BEEN AT MY LEVEL; I DO NOT THINK THERE WOULD HAVE BEEN SUFFICIENT TIME FOR EVASIVE ACTION. THERE IS NO REASON TO PUSH THESE LIMITS; AND I WILL BE MORE CONSERVATIVE IN THE FUTURE.