A LOW TIME COMMERCIAL PLT IN A GRUMMAN CHEETAH DIVERTS TO SEDONA ARPT WHEN UNABLE TO CLB TO ASSIGNED ALT IN PROX OF SEVERE TURB AND DOWNDRAFTS.

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WHILE ENRTE CLB FROM PRC TO ABQ; THE PLANE EXPERIENCED SEVERE DOWNDRAFTS AND UPDRAFTS. THE WX BRIEFING FORECAST SEVERE TURB. DURING THE CLB TO 11000 FT MSL; I ASKED FOR A BLOCK ALT BTWN 10500-11500 FT. THE CTR CTLR CLRED ME FOR A BLOCK ALT 11000-12000 FT. AT 10500 FT; I EXPERIENCED A DOWNDRAFT OF APPROX 700 FPM. FULL THROTTLE AND BEST CLB AIRSPD STILL SHOWED A 500 FPM DSCNT. AT 10000 FT THE ARTCC CTLR INFORMED ME OF THE MEA OF 10500 FT MSL. I INFORMED HIM THAT I WAS MVFR AND THAT I WOULD CANCEL IFR. THE TOPS WERE FROM 9500 FT TO 11500 FT AND WE WERE BARELY VFR. ABOUT THAT TIME I WAS FLYING OVER A CLR HOLE THAT EXTENDED TO THE GND. I ATTEMPTED TO CLB AND CONTINUE TO ABQ IN HOPES OF STAYING VFR ON TOP. UNFORTUNATELY; WHILE CIRCLING IN THE HOLE; I WAS UNABLE TO CLB. THE VSI DID NOT BUDGE INTO THE POSITIVE SIDE. THE CLR HOLE JUST HAPPENED TO BE OVER THE SEDONA ARPT. ONCE I HAD A VISUAL ON THE ARPT; I CANCELED FLT FOLLOWING AND DSNDED IN VFR CONDITIONS AND LANDED UNEVENTFULLY. OTHER ACFT ON FREQ WERE RPTING MODERATE TO SEVERE TURB. I SHOULD HAVE CLBED TO 11500 FT OVER DRK VOR; THEN DEPARTED. IF I COULDN'T SEE SEDONA; I WOULD HAVE TURNED BACK TO PRC AND SHOT THE VOR APCH.