A C210 CHARTER PLT; FLYING VFR; ENTERED IMC. EARLIER; HE HAD FLT INST FLUCTUATION AND WOULD NEED TO REVERT TO AN ALTERNATE STATIC SYS.

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INADVERTENT VFR AND IMC; LEVEL 4500 FT; WITH ZOA. THEY SAID; 'RADAR CONTACT LOST; SQUAWK VFR.' I NOTICED EARLIER THAT MY VSI WAS MAKING SHARP SWINGS PEGGING THE METER; INDICATING THAT THE ALTERNATE STATIC SOURCE SHOULD BE TURNED ON. WHILE WORKING THE PROB; I ENTERED THE CLOUDS. AT APPROX THE SAME TIME; MY VACUUM SYS STARTED FLUCTUATING. I SHIFTED MY FOCUS TO MY ELECTRIC TURN AND BANK INDICATOR AND TO MY ALT INDICATOR; ALONG WITH MY GPS. I WAS ABLE TO MAINTAIN LEVEL FLT AND FLEW ABOUT 15 MINS; TAKING BEARINGS OFF OF STOCKTON VOR AND MODESTO VOR TO MAINTAIN TERRAIN SEPARATION. I THEN CALLED STOCKTON APCH AND DSNDED TO VFR CONDITIONS. I SIGHTED BEACON LIGHTS AND VALLEY CITY LIGHTS. I WOULD HAVE DONE A 180 DEG TURN BACK TO VFR; BUT WORKING THE PROB WITH MY VACUUM AND STATIC INSTS; AND LOWER TERRAIN AHEAD; I ELECTED TO STAY LEVEL AND PROCEED TO VFR CONDITIONS. THE WX FORECAST I RECEIVED PRIOR TO DEPARTING GAVE ME A FEELING OF TOTAL VFR ALONG MY RTE. IN THE FUTURE; I WOULD DO A 180 DEG TURN BACK TO VFR AND LAND.