PVT PLT OF A C172 TOOK OFF FROM A NON CTLED ARPT AND FLEW AROUND THE TFC PATTERN WHEN THE RPTING WX INDICATED BELOW VFR MINIMUMS.

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PLANNED A SHORT FLT LCL TO MGY. I CHKED A COMPUTERIZED PROGRESS CHART AND NOTICED AN APCHING FRONT WITH SOME ASSOCIATED WX ACTIVITY. I CONTACTED THE DAY FSS FOR AN ABBREVIATED BRIEFING. MY MAIN CONCERN WAS WHEN THE FRONT WOULD ENTER OUR AREA. I WAS TOLD IT WOULD NOT BECOME A FACTOR UNTIL MUCH LATER THAT AFTERNOON. NO MENTION WAS MADE OF LESS THAN VFR VISIBILITY DURING THIS BRIEFING AND PERSONAL OBSERVATION DURING MY DRIVE TO THE ARPT INDICATED A TYPICAL HOT; HAZY SUMMER MORNING; WITH LITTLE OR NO CLOUDS. AFTER PREFLTING THE ACFT; I STARTED THE ENG AND TUNED IN THE AUTOMATED WX RPTING SYS (118.375 MHZ) ON THE FIELD TO MAKE A FINAL CHK OF WINDS AND ALTIMETER SETTING. I WAS SURPRISED TO FIND THE RPTED VISIBILITY TO BE ONLY 4 MI; BUT SINCE THIS WAS ABOVE VFR MINIMUMS; I CONTINUED WITH MY TAXI; RUNUP AND TKOF. IMMEDIATELY AFTER LIFTOFF; I REALIZED THAT THE VISIBILITY ALOFT WAS LOWER THAN I HAD EXPECTED. WHILE I COULD SEE A MICROWAVE TWR ABOUT 3 MI AWAY THAT IS COMMONLY USED AT OUR ARPT TO DETERMINE VFR MINIMUMS; I FELT THE WX TO BE BELOW MY 'PERSONAL MINIMUMS;' SO I REMAINED IN THE PATTERN; AND DURING MY DOWNWIND LEG; TUNED IN THE ATIS FOR DAY; ABOUT 15 MI TO THE N. I DISCOVERED THAT THEY WERE CALLING THE VISIBILITY 2 1/2 MI IN HAZE. I PROCEEDED DOWNWIND AND COMPLETED A NORMAL; UNEVENTFUL LNDG TO A FULL STOP. IN RETROSPECT; I REALIZE THAT I HAD FIXATED ON DETERMINING THE STATUS OF THE APCHING COLD FRONT AND HAD NEGLECTED TO GATHER OTHER APPROPRIATE WX INFO; SUCH AS THE CURRENT OR FORECAST VISIBILITY. I ALLOWED MYSELF TO BE FOOLED BY WHAT APPEARED TO BE CLR SKIES. THIS WILL BE AVOIDED IN THE FUTURE BY REVIEWING THE ENTIRE WX PICTURE AND NOT CONCENTRATING ON JUST 1 ASPECT OF IT.