GA SMA ALT DEVIATION EXCURSION FROM CLRNC ALT AND DEVIATION FROM CLRNC ROUTE.

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I HAVE BEEN NOTIFIED THAT AN INVESTIGATION IS BEING INITIALED CONCERNING 2 MATTERS ASSOCIATED WITH THIS FLT. ONE IS OF NO CONCERN. HOWEVER; 2 OTHERS ARE COLLECTIVELY REFERRED TO AS 'DEVIATIONS FROM FAR'S.' I WAS FLYING UNDER VFR CONDITIONS FROM SAC TO LAS; WHEN I ENCOUNTERED MODERATE TO SEVERE UP AND DOWN DRAFTS OVER THE SIERRAS. I MADE AN ATTEMPT TO MAKE A PIREP. I COULD NOT HOLD ALT TO WITHIN 100' OF MY ASSIGNED ALT. I FELT THAT IT WAS SAFER FOR ME TO CONCENTRATE ON LEVEL ATTITUDE AND MAINTAIN ALT TO WITHIN ABOUT 400'; WHICH WAS POSSIBLE. LATER I ENCOUNTERED AN ADDITIONAL IMPEDIMENT--2 THUNDERHEADS DIRECTLY IN MY PATH. I NOTIFIED CENTER OF THIS AND REQUESTED DEVIATION TO THE RIGHT OF COURSE. THEY INSTRUCTED ME TO CLB TO 15000'. I WAS NOT ABLE TO COMPLY AS I WAS AT MAX PWR AND CLB AIRSPD AND LOSING 200-500 FPM. AS I GOT WITHIN ABOUT 1 MI OF THE CUMULUS CLOUDS I DEVIATED TO THE RIGHT OF COURSE AND ASKED FOR VECTORS FOR THE NEAREST CLEAR ARPT. UPON LNDG IN TPH I WAS INFORMED THAT I HAD NUMEROUS DEVIATIONS FROM FAR'S AND WOULD HAVE TO ANSWER TO FAA. I FEEL THE DEVIATIONS WERE NEEDED DUE TO CONDITIONS AND I ACTED IN THE INTEREST OF SAFETY FOR MYSELF AND THE PLANE.