TB20 PLT ENCOUNTERS ICING AND IS UNABLE TO MAINTAIN ALT. DECLARES AN EMER; DSNDS OUT OF ICING AND DIVERTS TO ANOTHER ARPT FOR LNDG.

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I CHKED DUATS AND WX.COM BOTH ON THE EARLY MORNING OF THE FLT. THERE WAS AN AIRMET FOR MOUNTAIN OBSCURATION AND ICING FOR OVER THE MOUNTAINS. I CLBED TO 13500 FT MSL AND APCHED THE W SIDE OF THE MOUNTAINS TO ASSESS THE WX CONDITIONS AND FOUND HAZY LAYERS OF CLOUDS THAT POSED NO IMMEDIATE DANGER. THERE WAS A TAILWIND OF APPROX 40 KTS. I FOUND MYSELF IN A THIN CLOUD LAYER AND ATTEMPTED TO CLB OUT OF IT; BUT THE TAILWIND PUSHED ME DEEPER INTO THE CLOUDS VERY QUICKLY. I LOOKED DOWN TO MY WING AND FOUND A THIN LAYER OF ICE. I IMMEDIATELY TURNED AROUND TO ESCAPE THE CLOUDS; BUT WAS THEN FLYING INTO A 40 KT HEADWIND. THE ICE CONTINUED TO BUILD UP UNTIL I WAS UNABLE TO MAINTAIN ALT. BECAUSE I WAS MOVING SO SLOWLY OVER THE GND AND LOSING ALT; I CALLED UP CTR AND DECLARED AN EMER. I NAVED TOWARD ZZZ AND POPPED OUT OF THE CLOUDS AT AN ALT OF 9500 FT MSL. I CONTINUED ON TO ZZZ AND LANDED WITHOUT FURTHER COMPLICATION. MY PERCEPTION OF THE SITUATION BEFORE ICING OCCURRED WAS THAT I WAS SAFE ENOUGH TO OBSERVE THE WX ELEMENTS WITHOUT COMPROMISING VFR. BUT THE TAILWIND AND THE CHANGING DYNAMICS OF THE CLOUDS PUT ME IN IMC VERY QUICKLY. AS SOON AS I NOTICED ICE; I TURNED AROUND AND HEADED FOR THE NEAREST ARPT. HAVING SPENT A LOT OF FLT TIME IN IMC; I FELT COMFORTABLE NAVING AROUND IT; BUT HAD NEVER BEFORE EXPERIENCED ICING SO DID NOT CONSIDER THE DANGERS OF FLYING NEAR CONDITIONS SUITABLE FOR ICING. IN RETROSPECT; I FEEL THAT PERHAPS I WOULD HAVE BEEN BETTER SERVED BY CONTINUING ON WITHOUT TURNING AROUND GIVEN THE TAILWIND SINCE THERE WERE ACCESSIBLE ARPTS AHEAD OF ME TO THE E; BUT GIVEN THE FACTORS INVOLVED; I DID WHAT I HAD BEEN TRAINED TO DO.