ALTDEV AFTER INFLT ENCOUNTER WITH ADVERSE ENRTE WX FACTORS.

Narrative

I WAS FLYING AN SMA AT 11000 ON AN IFR FLT IN IMC CONDITIONS WHEN I ENCOUNTERED LIGHT RIME ICE ON THE LEADING EDGE OF THE WINGS. I EXPLAINED THE SIT TO THE AIR TFC CTLR AND ASKED IF COULD DSND TO 9000 FT. THE CTLR CLRED ME TO DSND TO 9500. AT 9500 THE TEMP WAS 0 DEGS C AND WHILE NO MORE ICE WAS ACCUMULATING ON THE WINGS; IT WAS NOT DEFROSTING EITHER. WHILE DISCUSSING WITH ATC THE POSSIBILITY OF DIVERTING S TO SAN MARCOS (RZS) VOR ALONG V-25 (WHERE THE MEA IS 8600) AND THEN DIRECT VTU; LAX; AND FINALLY TO LGB; I HIT AN UPDRAFT WHICH CAUSED THE ACFT TO CLB. WHILE APCHING 10500 FT; I ASKED ATC IF I COULD CLB TO 11000 FT. AT 11000 IT WAS VFR; BTWN 2 LAYERS OF CLOUDS. THE CTLR ASKED ME WHAT MY PRESENT ALT WAS. I TOLD HIM 10500. HE ASKED ME WHO GAVE ME PERMISSION TO CLB TO 10500. I PAUSED; THEN REPLIED BY EXPLAINING HOW AN UPDRAFT CAUSED ME TO CLB AND I CONTINUED TO 10500 WHICH WAS CLR OF CLOUDS. THE CTLR SCOLDED ME FOR CLBING WITHOUT PERMISSION AND CLRED ME BACK TO 11000 WHERE IT WAS VFR. I THANKED HIM FOR HIS HELP AND CHANGED FREQS TO THE NEXT CTLR. IT WAS CLR TO ME; AS A PLT; IT WAS MORE IMPORTANT TO REACH AN ALT THAT WAS CLR OF CLOUDS AND MOISTURE TO STOP THE BUILD-UP OF ICE; THAN TO CONTINUE TO MAKE A MARGINAL SIT WORSE. I COULD NOT CTL THE AIR MASS THAT CAUSED THE ACFT TO CLB INITIALLY. WHEN I GOT OUT OF THE UPDRAFT; I WAS ONLY A COUPLE HUNDRED FT FROM 10500; AND MORE IMPORTANTLY; A COUPLE HUNDRED FT FROM VFR CONDITIONS. I CLBED TO 10500 BECAUSE THE AERODYNAMICS OF AN AIRPLANE ARE MUCH BETTER THAN AN ICE CUBE.