FAILING TO ABIDE BY HIS OWN PARAMETERS FOR CONTINUING FLT INTO DETERIORATING CONDITIONS; NON-INSTRUMENT RATED PRIVATE DA20 PLT FLIES INTO IMC CONDITIONS. ATC PROVIDES ASSIST TO A VMC ARRIVAL AT AN ALTERNATE ARPT.

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I WAS ON A LONG XCOUNTRY FROM NORTHERN OHIO BACK TO ORL. EXCELLENT VFR WX WAS FORECAST AND OBSERVED ALONG THE ENTIRE RTE UNTIL ARRIVING AT THE FLORIDA BORDER NEAR JACKSONVILLE. I HAD BEEN BRIEFED ON CONDITIONS IN FLORIDA; WITH BROKEN CEILINGS RPTED AS LOW AS 2400 FT; POSSIBILITY OF POCKETS OF LOWER CEILINGS AND RAIN. I WAS MONITORING THE SITUATION CLOSELY ON SATELLITE DATALINK WX/GPS MOVING MAP. MY INTENTION WAS TO FLY OVER THE JACKSONVILLE AREA; WHERE THERE IS PLENTY OF GND LIGHTING AND NUMEROUS ARPTS SUITABLE FOR AN UNPLANNED LNDG IF WX PROVED TOO MARGINAL. AT THE TIME I APCHED THE AREA; VISIBILITY WAS VERY GOOD; CEILINGS WERE ABOVE 2000 FT; AND AREAS OF PRECIP (AS INDICATED BY SATELLITE WX AND CORROBORATED BY VISUAL OBSERVATIONS FROM THE COCKPIT) WERE SMALL AND EASILY 'CIRCUMNAVIGATEABLE.' RPTED TEMP/DEWPOINT SPREADS WERE ABOUT 6 DEGS. GIVEN THAT I HAVE HUNDREDS OF HRS OF NIGHT VFR; AND HUNDREDS OF HRS OF INTERPING SATELLITE WX RADAR DATA AS DISPLAYED ON THE GARMIN UNITS; I WAS CONFIDENT I COULD SAFELY COMPLETE THIS FLT THROUGH THIS AREA WITHOUT INCIDENT; AND WAS PREPARED TO LAND AT AN ALTERNATE ARPT AS NECESSARY. MY FIRST SIGNS OF IMPENDING TROUBLE WERE OBSERVED WHEN PASSING AROUND THE NAVY ARPT S OF JAX. CEILINGS WERE DROPPING SUDDENLY. AT 1200-1300 FT MSL; I WAS BELOW THE CLOUDS BY LEGAL VFR MARGINS; HOWEVER; HALO EFFECTS WERE BEGINNING TO APPEAR AROUND GND LIGHTS. I CHKED; AND TEMP/DEWPOINT SPREADS HAD DROPPED TO ABOUT 2 DEGS. CONDITIONS WERE STILL MVFR AT THIS POINT; YET LOWER THAN I HAD ANTICIPATED. IN RETROSPECT; I SHOULD HAVE IMMEDIATELY DETERMINED THE CLOSEST SUITABLE ARPT AND TERMINATED THE FLT. HOWEVER; I NOTED THAT I WAS ONLY 25 MINS FROM MY DEST; AND THAT CONDITIONS AHEAD AT ORLANDO; SANFORD; AND OTHER ARPTS TO THE S AND W WERE STILL RPTING GOOD VFR. RATHER THAN TURNING AROUND AND LNDG BEHIND ME WHERE WX WAS DETERIORATING QUICKLY; I ELECTED TO PROCEED AHEAD TOWARD MY DEST WHERE WX WAS RPTED MUCH BETTER. LOOKING BACK; I THINK THE INFAMOUS 'GET THEREITIS' PLAYED A ROLE IN MY DECISION. ONCE S OF THE JAX AREA; PROBABLY ABOUT 1/2 WAY BTWN FLAGLER; CO; ARPT AND PALATKA ARPT; I NOTICED CONDITIONS WERE NOT IMPROVING AT ALL; AND DECIDED TO TURN BACK TOWARD AREAS OF BETTER LIT TERRAIN FOR LNDG AT AN ALTERNATE FIELD. IMMEDIATELY UPON BEGINNING THIS TURN; CONDITIONS SUDDENLY WENT SOLID IFR. I WAS EITHER IN A CLOUD; OR TEMP/DEWPOINT HAD SUDDENLY CONVERGED AND CREATED INSTANTANEOUS FOG. I HAD ZERO VISIBILITY AND ZERO GND REF. I IMMEDIATELY BRIGHTENED THE INTERIOR (INST) LIGHTS SO AS TO FOCUS ON MY INSTS; LEVELED THE WINGS; AND PUT THE ACFT IN A CLB. I DECLARED AN EMER TO DAYTONA APCH AND FOCUSED ON MAINTAINING CTL OF THE AIRPLANE IN A CLB. I CHOSE TO CLB BECAUSE I WAS AT LOW ALT AND I HAD HEARD OTHER VFR PLTS RPT THAT THERE WERE AREAS OF GOOD VISIBILITY AND GND REF ABOVE ME. SOON; I EMERGED ABOVE THE IMC AND COULD SEE GND. DAYTONA VECTORED ME TO ZZZ AND ASSISTED BY PROVIDING RWY; LIGHTING; AND FREQ INFO SO I COULD FOCUS ON FLYING THE AIRPLANE. I LANDED SUCCESSFULLY AT ZZZ AND SPENT THE NIGHT THERE -- WAITING FOR BETTER DAYLIGHT WX TO TRY AGAIN. LESSONS LEARNED: I SUCCUMBED IN PART TO A DESIRE TO GET HOME THAT NIGHT MANY HRS OF NIGHT FLT AND NAVING AROUND LIGHT TO MODERATE PRECIP HAD CONTRIBUTED TO A FALSE SENSE OF SECURITY. ALSO; AT THE FIRST SIGN OF THINGS NOT GOING AS PLANNED; I PASSED ON OPPORTUNITIES TO SAFELY END THE FLT EARLY. I SHOULD HAVE TERMINATED THE FLT AT THE FIRST SIGN OF DROPPING CEILINGS AND CONVERGING TEMP/DEWPOINT. I HAVE SINCE INCREASED MY NIGHT FLT PERSONAL MINIMUMS.