A PA31 ENTERED IMC WHILE ENRTE OVER MOUNTAINOUS TERRAIN. THE PLT CLBED VFR IN IMC; CALLED APCH CTL AND RETURNED IFR TO HIS DEP ARPT.

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ON A VFR FLT I ENCOUNTERED RAPIDLY DETERIORATING VISIBILITY/CEILING CONDITIONS; THIS SIT WAS COMPOUNDED BY A FLT PATH LEADING INTO RISING TERRAIN AND A NARROWING VALLEY. HAVING BEEN RELEASED FROM CTL BY ZZZ DEP APPROX 5 MINS PRIOR; AND UNCOMFORTABLE WITH DSNDING ANY LOWER (SCUD RUNNING); THE ACFT ENTERED IMC. GIVEN THE FACT THAT I AM VERY FAMILIAR WITH THE LCL AREA; THE TERRAIN ELEVATIONS; AND THE APCH CORRIDORS; RATHER THAN ATTEMPT TO DSND TRYING TO FIND VMC; I ELECTED TO CLB IN IMC TO A SAFE ALT WHERE I DID FIND AND RPT AN 'IN BTWN LAYER' FOR A BRIEF PERIOD WHEN I RE-ESTABLISHED CONTACT WITH ZZZ1 APCH. I THEN RPTED MY INABILITY TO MAINTAIN VFR AND REQUESTED AN IFR CLRNC BACK TO ZZZ1. APCH CTL ISSUED A NEW XPONDER CODE ALONG WITH A REQUEST TO 'IDENT' AND AFTER A BRIEF DELAY WHICH NECESSITATED ANOTHER REQUEST FOR CLRNC; I RECEIVED IFR INSTRUCTIONS TO PROCEED AND THE REMAINDER OF THE FLT WAS UNEVENTFUL. OBSERVATION: PRIOR TO FLT; I CALLED THE AWOS AT ZZZ2 AND RECEIVED A RPT OF CALM WINDS; GREATER THAN 10 SM VISIBILITY; FEW AT 300 FT SCATTERED AT 2700 FT; AND 3500 FT OVCST; FEELING COMFORTABLE WITH THE DEST RPT AND THE APPARENT DSCNT CONDITIONS I OBSERVED IN MY DIRECTION OF FLT FROM THE GND; I DECIDED TO GO. CAUSAL FACTORS: THE LACK OF ANY RTE OF FLT WX RPT; THE LACK OF ANY FLYABLE APCH PROC (BASED ON ACFT EQUIP); THE APPARENT FLYABLE VMC; AND THE DESIRE TO GET CUSTOMERS TO THEIR SCHEDULED DEST. FUTURE CONSIDERATIONS: I WILL DO A BETTER JOB OF EVALUATING THE AVAILABLE CURRENT/FORECAST CONDITIONS; WHICH I CAN PRESENT TO THE PAX WITH A MORE REALISTIC ASSESSMENT (BASED ON ENVIRONMENTAL CONDITIONS; IE; WX TERRAIN; ETC) VERSUS THE PRESENT ENTHUSIASTIC 'CAN DO' ATTITUDE.