PA32-300; CHEROKEE 6 PLT MAKES EMER LNDG ON HWY WHEN WX CLOSES IN AROUND HIM.

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I WAS FLYING MY PA32-300 (CHEROKEE 6) FROM CNY TO MY HOME BASE; TRK VIA SALINA; UT; THENCE TO MLF AND MVA. ABOUT HALFWAY BTWN MLF AND MVA I ENCOUNTERED INCREASING TURB AND RAPIDLY DETERIORATING VISIBILITY. I DECIDED TO CHANGE COURSE TO THE NEAREST ARPT; TPH. I RADIOED FOR CONDITIONS AND WAS TOLD TPH WAS IFR (I AM PRESENTLY VFR ONLY). MY SIT WAS THAT ALL QUADRANTS WERE NOW IFR. I DECIDED TO PUT DOWN WHERE I WAS AND MADE AN OFF FIELD LNDG 79 SM E OF TPH ON US 6. I LNDED SAFELY AND REMAINED OVERNIGHT IN TPH. I RETURNED NEXT DAY; TOOK OFF AND CONTINUED ON TO TRK. INCIDENTLY; THERE IS A CLOSED FIELD JUST W OF WHERE I PUT DOWN THAT I AM NOW TOLD AND SAW IS JUST 10 NM FROM MY POS THAT HAS A BRAND NEW 7000 FT RWY BELONG TO THE AIR FORCE. HAD IT SHOWN ON THE CHART AS A REAL ARPT; I WOULD NOT HAVE BEEN IN THE DANGER THAT I WAS. SEE LAS VEGAS SECTIONAL N38:20:00 W116:16. I WAS ADVISED THAT VFR WAS NOT RECOMMENDED FOR W NV AND THE SIERRA DUE TO OBSCURATION; TURB; ETC. HOWEVER; MY (VERY) LIMITED EXPERIENCE WITH FLT SVC IS THAT THEY ALMOST ALWAYS SAY 'VFR NOT RECOMMENDED.' I TRIED TO PUSH IT. I GOT LUCKY; GOD SMILED; KISSED ME AND MADE IT GOOD.