MOONEY 20 PLT ENCOUNTERS SEVERE TURB NEAR FJS AND LOSES 2000 FT.

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FLYING ON V23 AT 10000 FT; THE MEA; TO STAY BELOW THE FREEZING LEVEL. IT WAS +2 DEGS C AT 10000 FT MSL. BRIEFING HAD AIRMET FOR OCCASIONAL LIGHT TO MODERATE TURB. RIDE FROM ZZZ TO S OF SHASTA WAS UNEVENTFUL WITH AN OCCASIONAL VERY LIGHT BUMP. A COUPLE OF MI S OF FJS WE ENCOUNTERED SEVERE TURB; HITTING HEADS A FEW TIMES AND THROWING THE PLANE. WE LOST CLOSE TO 2000 FT BEFORE GAINING CTL OF THE PLANE -- 60 DEGS OFF COURSE AND STILL LOSING ALT. AS I BROUGHT THE NOSE UP TO ARREST THE DSCNT WE 'POPPED' OUT OF THE CLOUDS AND I SAW SCOTT VALLEY BELOW. I POINTED THE PLANE TO A30 AND FINALLY COMMUNICATED WITH ZOA THROUGH ANOTHER PLANE AND THEN CANCELING WITH ZSE BEFORE LNDG AT A30. WX/WINDS WERE WORSE THAN FORECAST AND HINDSIGHT SAYS I SHOULD NOT HAVE MADE THAT TRIP BELOW 14000 FT. SEEMS LIKE WE HIT A MOUNTAIN WAVE COMING OFF THE 7000-8000 FT PEAKS TO THE W. BEING ONLY 2000 FT ABOVE THAT TERRAIN IN IMC WAS NOT A GOOD IDEA. I WAS TRYING TO REMAIN BELOW THE FREEZING LEVEL TO STAY OUT OF ICE ALTHOUGH WE DID HAVE A TKS DEICE SYS. A BETTER CHOICE WOULD HAVE TO BEEN 90 DEGS AT 16000 FT OR 14000 FT AND IF ICE WAS FOUND DO A 180 DEGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE FELT LUCKY TO COME OUT OF THE CLOUDS OVER A30. THE PLANE REMAINED AT A30 UNTIL HE COULD RETRIEVE IT A WK LATER. THE RPTR FEELS THAT MORE INFO SHOULD BE AVAILABLE ABOUT THE POTENTIAL FOR SEVERE TURB IN THIS AREA.