GA SMA PLT ENCOUNTERS ICING. ENRTE WX WAS NOT THE WX FORECAST. DIVERSION TO ALTERNATE.

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THE FLT WAS DELAYED FROM OCT/XA/95 TO OCT/XB/95 TO ALLOW A STRONG COLD FRONT TO PASS. ON EARLY MORNING OCT/XB/95; A CALL TO FLT SVC REVEALED IMC ALONG RTE OVER THE MOUNTAINS WITH GOOD VFR AT DEST 3N8 (CONCORD; NC). DEP POINT WAS VFR (AGC-ALLEGHENY COUNTY) WITH TOPS UNKNOWN. ICING WAS FORECAST IN CLOUDS AND PRECIPITATION MAINLY E OF OUR RTE. A COUPLE OF HRS LATER (APPROX AM EDT) PRIOR TO DEP ANOTHER CALL TO FSS REVEALED TOPS AT APPROX 6000 FT; WITH UNLIMITED VISIBILITY ON TOP. ICING WAS FORECAST (MIXED/MODERATE RIME) MAINLY E OF OUR COURSE AND AT LOW ALTS. THE BRIEFER WAS VERY OPTIMISTIC ABOUT OVERFLYING THE ICING CONDITIONS IF THEY WERE TO MATERIALIZE. WE DEPARTED AND CLBED THROUGH A 1500 FT LAYER TO BREAK OUT ON TOP AT 4000 FT. OVER A PERIOD OF APPROX 100 MI; THE TOPS SLOWLY SLANTED UP AND I CONTINUED TO CLB TO HIGHER ALTS TO STAY ON TOP. CTR DELAYED A REQUEST FOR A CLB FROM 9000-10000 FT. OTHERS ON THE FREQ STARTED COMPLAINING ABOUT ICE. AFTER A HDOF; I REQUESTED A CLB AGAIN TO AVOID IMC CONDITIONS. THERE WAS A DELAY AND WE ENTERED THE TOPS AT 9000 FT. ALMOST IMMEDIATELY; WE ENCOUNTERED ICING. THE ACFT WOULD NOT CLB AND THE PROP WAS AFFECTED THE MOST. I IMMEDIATELY ASKED; AND RECEIVED A CLB CLRNC AND THEN TOLD ATC I WAS DOING A 180 DEG TURN. ATC WAS VERY WILLING TO HELP OUT AFTER THE ENCOUNTER BUT WERE SLOW IN HELPING OUT BEFORE THE ENCOUNTER. WE BROKE OUT ON TOP NEAR THE ELKINS VOR AND CLBED IN A HOLD TO REACH 11000 FT BEFORE CONTINUING ON COURSE. EVENTUALLY WE CLBED TO 13000 FT TO REMAIN ON TOP. UPON REACHING VMC TO THE GND; WE CANCELED IFR AND LANDED AT A NEARBY ARPT TO REFUEL AND REFRESH. THE REMAINDER OF THE TRIP WAS COMPLETED IN GOOD VFR. I HAD BEEN LED TO BELIEVE THAT THE TRIP WOULD BE OUTSIDE OF ICING CONDITIONS BY THE SECOND BRIEFER. THE PIREPS ON THE ACTUAL CONDITIONS WERE APPARENTLY INACCURATE OR CONDITIONS HAD CHANGED RAPIDLY. THE FORECAST HAD NOT HELD UP TO THE GOOD VFR AND/OR LIGHT IFR CALLED FOR BY FSS AND THE WX CHANNEL. OUR GND SPD WAS VERY SLOW AT 13000 FT DUE TO WINDS ALOFT VERY STRONG OUT OF THE S. I HADN'T GOTTEN THESE WINDS FORECAST ORIGINALLY SINCE IT WASN'T SEEMINGLY NEEDED. SINCE THIS FLT I HAVE ALSO REFLECTED ON WHAT I WOULD HAVE DONE HAD I NEEDED TO MAKE A DIVERSION TO A NEARBY ARPT THROUGH ICING HAD SOME EMER OR MALFUNCTION OCCURRED. I KNEW THAT GOOD VFR WAS NEARBY AND WELL WITHIN OUR RANGE EVEN WITH THE EXTRA SLOW GND SPD THAT WE EVENTUALLY ENCOUNTERED. I LEARNED A LOT THAT DAY AND WILL MAKE THE 180 DEG CLB OR DSCNT IMMEDIATELY IF I EVER EXPERIENCE THIS AGAIN. I'LL NEVER DEPART IF ICING IS EVEN CLOSE TO MY RTE.