A BE33 PLT; CRUISING AT 14000 FT 30 NM E OF ALS; ENCOUNTERED A MOUNTAIN WAVE DOWNDRAFT; REQUIRING HIM TO DSND IN ORDER TO REGAIN ACFT SPD CTL.

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I WAS ON AN IFR FLT PLAN CRUISING ON V210 TO ALAMOSA AT 14000 FT. I WAS IN AND OUT OF IMC. RIDE WAS SMOOTH. ABOUT 15 NM E OF BLOKE INTXN; I ENCOUNTERED SIGNIFICANT HEADWIND AND DSNDING MOUNTAIN WAVE. I PITCHED UP TO MAINTAIN ALT (MEA IS 14000 FT) AND APPLIED FULL PWR. AS MY AIRSPD DECREASED TO JUST ABOVE STALL (THE STALL WARNING HORN SOUNDED); I NEEDED TO PITCH DOWN SLIGHTLY AND WAS UNABLE TO MAINTAIN ALT. I NOTED A GPS GND SPD OF 9 KTS. I CALLED TO INFORM ZDV. THE CTLR REMINDED ME OF THE MEA. I DSNDED TO NOT LOWER THAN 13000 FT BEFORE I WAS OUT OF THE WAVE AND ABLE TO CLB AND MAINTAIN 14000 FT. I DID MAINTAIN OCCASIONAL SIGHT OF AND REF TO TERRAIN. I ENTERED VISUAL CONDITIONS; CANCELED IFR AND PROCEEDED TO ALAMOSA; CO. I HAVE FLOWN THIS RTE NUMEROUS TIMES AND HAVE NEVER ENCOUNTERED SUCH A MOUNTAIN WAVE. IN THE FUTURE; I WILL FLY THIS RTE AT NOT LESS THAN 16000 FT MSL WHEN IN IMC. I CONSIDERED A 180 DEG TURN TO LEAVE THE DOWNDRAFT BUT WITH MY AIRSPD SO CLOSE TO A STALL; I FELT IT WAS NOT WISE. I SHOULD HAVE TURNED AROUND AT THE FIRST SIGN OF DOWNDRAFT INSTEAD OF ASSUMING IT WOULD BE ONLY SHORT-LIVED. I KNOW THE PRINCIPLE OF FLYING FAST THROUGH DOWNDRAFTS BUT HIGH TERRAIN NECESSITATED MY EFFORTS TO MAINTAIN ALT.