SMA ENCOUNTERS MOUNTAIN WAVE DOWNDRAFTS; UNABLE HOLD ASSIGNED ALT. CTLR SUGGESTS 180 TURN AS DSNDING BELOW RADAR VECTORING ALT. RPTR TURNS; CLBS; CONTINUES ON ORIGINAL COURSE.

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DEPARTED BFL IN SMA ON IFR FLT PLAN FROM BFL TO BUR; CLRED TO BUR VIA RADAR VECTORS LAKE HUGHES VOR (LHS); LHS.LYNXX6 ARR; MAINTAIN 9000. TRACKING 140 DEGS INBOUND TO LHS; RTE OF FLT CROSSES TEHACHAPI MOUNTAINS; WESTERN CORNER OF ANTELOPE VALLEY; AND LHS VOR IN THE SAN GABRIEL MOUNTAINS. SOUTHERLY WINDS APPROX 20 KTS AND GREATER SET UP MOUNTAIN WAVE ACTIVITY IN VICINITY OF THESE MOUNTAIN RANGES; AND THE RANGES WERE MOSTLY OBSCURED IN CLOUDS; MOST TOPS ESTIMATED AT 8000; BUT WITH SEVERAL BUILDUPS OVER 9000; AND OCCASIONAL BUILDUPS BEYOND 11000 WITHIN 10 NM OF RTE. A SIGNIFICANT STORM WITH TOPS GREATER THAN 30000 WAS WITHIN 50 MI TO THE W; BUT WAS NOT A FACTOR IN THIS FLT. VISIBILITY OUTSIDE OF CLOUDS WAS UNRESTRICTED. APPROX 20 NM NW OF LHS; APCHING TEHACHAPI MOUNTAINS; ENCOUNTERED DOWNDRAFT FROM MOUNTAIN WAVE. SLOWED TO BEST RATE OF CLB AND WAS STILL LOSING 300-500 FPM. ADVISED LA CTR CTLR THAT I WAS UNABLE TO MAINTAIN ALT (WAS PROBABLY DOWN TO 8500-8600 BY THIS TIME); CTLR ASKED FLT CONDITIONS; WHICH WERE STILL VMC BUT WOULD ENTER IMC WITHIN A HALF MI. CTLR ADVISED THAT WE WERE DSNDING BELOW A MIN VECTORING ALT; AND RECOMMENDED 180 DEG TURN AND RETURN TO BFL. I REQUESTED AND WAS APPROVED FOR A DEV TO THE W; INTENDING TO ATTEMPT A LOOK AROUND THE BUILDUP THAT WAS IN MY INTENDED FLT PATH. STILL LOSING ALT; IT QUICKLY BECAME CLR THAT THIS DEV WAS NOT WORKABLE; SO I CONTINUED A TURN TO APPROX 310. ASKED INTENTIONS; I REQUESTED A CLB TO 11000 TO MAKE ANOTHER ATTEMPT AT HIGHER ALT; WHICH WAS APPROVED. THE CTLR CHKED WITH ANOTHER ACFT SMA X WHICH HAD JUST MADE THE SAME XING AT 11000; AND HAD LOST CONSIDERABLE AIRSPD IN ORDER TO MAINTAIN ALT; BUT HAD BEEN ABLE TO GET THROUGH. WE HAD TO FLY SEVERAL MI N TO GET OUT OF THE DOWNDRAFT; PROBABLY DROPPING BELOW 8000 AT ONE POINT; BUT EVENTUALLY WERE ABLE TO CLB; AND ONCE WE REACHED 10000; THE CTLR TURNED US BACK TO LHS; AND WE WERE ABLE TO CONTINUE A CLB TO 11000. IN FACT; UPDRAFTS CARRIED US TO AS HIGH AS 11400. AS WE ENTERED THE DOWNDRAFT AGAIN; THE CTLR CLRED US FOR A GRADUAL DSCNT BACK TO 9000. STARTING OUR XING AT 11000 WITH PLENTY OF CLOUD CLRNC; AND MAINTAINING BEST RATE OF CLB; WE STILL LOST BTWN 100-500 FPM; DSNDING; I BELIEVE; TO JUST UNDER 9000 IN VMC BEFORE XING INTO THE WINDWARD UPDRAFTS; WHICH CARRIED US TO ALTS VARYING BTWN 9500 AND 10000 AS WE CROSSED THE ANTELOPE VALLEY. WITHIN 5 NM OF LHS WE ENCOUNTERED THE LEEWARD DOWNDRAFTS OF THE NEXT MOUNTAIN RANGE. STARTING AT ABOUT 9500; WE LOST 100-200 FPM; FINALLY BREAKING OUT OF THE DOWNDRAFTS AT ABOUT 8600; STILL MAINTAINING VMC. AT SOME POINT IN THIS PERIOD; ASKED BY CTLR OF CONDITIONS; I RESPONDED THAT I WAS STILL LOSING 100 FPM; BUT THAT I HAD ADEQUATE CLOUD CLRNC TO COMPLETE THE XING IN VMC AND WOULD CONTINUE. BEYOND LHS; WITH BURBANK APCH; THE REMAINDER OF THE FLT WAS UNEVENTFUL; ALTHOUGH AT TIMES IT WAS STILL DIFFICULT TO MAINTAIN ASSIGNED ALT; MORE DUE TO UPDRAFTS. WHILE THE FLT WAS COMPLETED SUCCESSFULLY; I HAVE SPENT SOME TIME SECOND GUESSING MY ACTIONS. BASED ON MY WX BRIEFINGS (WHICH WERE REASONABLY ACCURATE); SHOULD I HAVE EVEN ATTEMPTED THIS FLT? ONCE ENCOUNTERING DIFFICULTY; SHOULD I HAVE RETREATED TO BAKERSFIELD? BASED ON CONDITIONS; COULD I HAVE PLANNED MY XING DIFFERENTLY? DID I COMMUNICATE MY PREDICAMENT AND INTENTIONS ACCURATELY AND IN A TIMELY MANNER TO ATC?