IMC IN VFR FLT AS FLYING RANCHER FLIES INTO SNOW STORM.

Narrative

I FLEW TO MY RANCH FROM THE PIERRE MUNICIPAL ARPT. THE RANCH IS ABOUT 20 MI S OF PIERRE. WHEN I LEFT THE RANCH TO RETURN TO PIERRE; THE VISIBILITY WAS GOOD. HOWEVER; AS I APCHED THE MISSOURI RIVER IT BECAME HAZY. I THOUGHT THAT CONDITIONS WOULD IMPROVE AFTER I CROSSED THE RIVER AND THAT THE ARPT WOULD BE VFR. INSTEAD; I FLEW INTO A SNOW SQUALL AND THE VISIBILITY DECREASED MARKEDLY. I CIRCLED 2 OR 3 TIMES TO SEE IF I COULD RETURN TO THE RANCH BUT THE RIVER BREAKS HAD BECOME OBSCURE. BECAUSE OF HVY SNOW COVER IN THE FIELDS BTWN THE RIVER AND HWY 34; I DECIDED TO LAND ON HWY 34. I LANDED E OF PIERRE ON HWY 34 AND PULLED THE PLANE INTO A GREENHOUSE PARKING LOT. THE GREENHOUSE IS CLOSED DURING THE WINTER. AN FBI AGENT OBSERVED MY LNDG AND GAVE ME A RIDE TO THE ARPT. THE FOLLOWING MORNING I TOOK MY UNCLE TO THE SITE TO WATCH FOR TFC AS I TOOK OFF FOR THE ARPT. THE ONLY TFC I OBSERVED ON BOTH LNDG AND TKOF WAS THE CAR BELONGING TO THE FBI AGENT WHO ASSISTED ME. MY AIRPLANE IS A PIPER PA18; 90 HORSEPWR WITH INOPERATIVE RADIO.