Narrative:

I was en route from the slc area to dij. I evaluated the WX over soda springs; identification (U78) and decided that it was VFR to driggs; identification (dij). While en route between soda springs and dij; the WX started to come down. At about the halfway point; I decided to turn 180 degrees for afo by way of soda springs (U78). Once en route for afo at the top of tin cup pass; the WX came down more and it was no longer VFR to afo. I turned 180 degrees again back toward soda springs only to have the WX coming down there also. Over the course of the next 5 mins; it became apparent that I was running out of options and decided to make an emergency landing on a state highway. At that point; the conditions had come down to about 1 mi; ceiling 500-750 ft. The landing was successful with no damage. I pulled the plane off the highway and got a ride from a passing motorist. Earlier that day; I had gotten a standard WX brief and was aware that WX was moving in but that by my calculations I would have been ahead of it. Additionally; the radar information on my garmin 496 confirmed my conclusions. Having flown in the mountains for more than 1000 hours; I have never seen the WX come down like a blanket the way it did that day. Contributing factors: overconfidence in knowing the terrain and the local WX. I was tired from flying all day. Next time I will not push the WX.

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Original NASA ASRS Text

Title: SMALL AIRCRAFT PILOT REPORTS RAPIDLY DETERIORATING WEATHER WHICH BLOCKS ATTEMPTS AT DIVERSION AND RESULTS IN SAFE LANDING ON STATE HIGHWAY.

Narrative: I WAS ENRTE FROM THE SLC AREA TO DIJ. I EVALUATED THE WX OVER SODA SPRINGS; ID (U78) AND DECIDED THAT IT WAS VFR TO DRIGGS; ID (DIJ). WHILE ENRTE BTWN SODA SPRINGS AND DIJ; THE WX STARTED TO COME DOWN. AT ABOUT THE HALFWAY POINT; I DECIDED TO TURN 180 DEGS FOR AFO BY WAY OF SODA SPRINGS (U78). ONCE ENRTE FOR AFO AT THE TOP OF TIN CUP PASS; THE WX CAME DOWN MORE AND IT WAS NO LONGER VFR TO AFO. I TURNED 180 DEGS AGAIN BACK TOWARD SODA SPRINGS ONLY TO HAVE THE WX COMING DOWN THERE ALSO. OVER THE COURSE OF THE NEXT 5 MINS; IT BECAME APPARENT THAT I WAS RUNNING OUT OF OPTIONS AND DECIDED TO MAKE AN EMER LNDG ON A STATE HWY. AT THAT POINT; THE CONDITIONS HAD COME DOWN TO ABOUT 1 MI; CEILING 500-750 FT. THE LNDG WAS SUCCESSFUL WITH NO DAMAGE. I PULLED THE PLANE OFF THE HWY AND GOT A RIDE FROM A PASSING MOTORIST. EARLIER THAT DAY; I HAD GOTTEN A STANDARD WX BRIEF AND WAS AWARE THAT WX WAS MOVING IN BUT THAT BY MY CALCULATIONS I WOULD HAVE BEEN AHEAD OF IT. ADDITIONALLY; THE RADAR INFO ON MY GARMIN 496 CONFIRMED MY CONCLUSIONS. HAVING FLOWN IN THE MOUNTAINS FOR MORE THAN 1000 HRS; I HAVE NEVER SEEN THE WX COME DOWN LIKE A BLANKET THE WAY IT DID THAT DAY. CONTRIBUTING FACTORS: OVERCONFIDENCE IN KNOWING THE TERRAIN AND THE LCL WX. I WAS TIRED FROM FLYING ALL DAY. NEXT TIME I WILL NOT PUSH THE WX.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.