PLT OF SMT FREIGHTER ON SPECIAL VFR FLT PLAN ENCOUNTERED IMC AT 550 MSL.

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I NEEDED A SPECIAL VFR TO EUREKA. FAR 135 DOESN'T ALLOW ME TO DO AN APCH THERE SINCE NO WX IS RPTED AT EUREKA MURRAY ONLY ARCATA. CEILING WAS RPTED AS 600 FT; 2 MI VISIBILITY. ALSO; A PIREP AT EUREKA WAS BASES AT 600 VISIBILITY 4-5 MI. DURING THE SPECIAL VFR I ENCOUNTERED LOWER WISPS OF CLOUD SO THIN ONE COULD SEE THROUGH THEM. I DECIDED TO CONTINUE. I MOMENTARILY LOOKED DOWN TO PICK UP MY SECTIONAL. WHEN I LOOKED UP AGAIN I WAS ENTERING A SCUD LAYER THAT WAS THICKER THAN THE REST. BEFORE I COULD REACT I WAS IMC. I WAS BEGINNING TO CLB; MIXTURES AND PROPS MOVED FORWARD; AND JUST AS QUICKLY POPPED BACK OUT OF THE SCUD LAYER. I WAS STILL AT ABOUT 500-600 FT. I NOW HAD 5 MI VISIBILITY; I COULD SEE ACROSS ARCATA BAY TO EUREKA MURRAY ARPT. I ELECTED TO CONTINUE AND LAND. I FEEL I NEEDED TO WATCH FURTHER AHEAD AND HAVE CHARTS MORE READILY AVAILABLE. IT MAY ALSO HELP IF ACV WX COULD BE USED FOR THE APCH AT EUREKA MURRAY. IT WAS THAT MOMENT OF INATTN OUT THE WINDOW THAT CAUSED MY PROBLEM; IN SUCH MARGINAL CONDITIONS.