ACR X ALTDEV DUE TO TURB.

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INBOUND ON STAR ARR FROM E WITH EXTENSIVE DETOURING E OF DENVER. ACR X AT 11000 FT OBSERVED EXTENSIVE CLOUDS AND VIRGA AHEAD. TEMPERATURE AND DEWPOINT SPREAD MORE THAN 50 DEG F; AND LOW LEVEL WINDSHEAR ALERTS ACTIVE AT DEN CAUSED ME TO BE VERY ALERT FOR SEVERE WX. MY COMPANY ADVISES ITS PLTS TO 'NOT FLY UNDERNEATH VIRGA' IF POSSIBLE. WHILE STILL ABOUT 20 MI FROM THE VIRGA; I REQUESTED LOWER ALT AND WAS TOLD BY APCH IT WOULD BE 'ABOUT 7 MORE MI.' AFTER 10 MI OR SO I AGAIN REQUESTED LOWER. NO ANSWER FROM ATC. SHORTLY AFTER; TURB BEGAN THAT RAPIDLY INCREASED TO MODERATE WITH A FEW SEVERE JOLTS. ACFT ROLLED UP TO 20 DEGS AND PITCHED UP ABOUT 10 DEGS WITH A 20 KTS LOSS OF AIRSPD. I ASKED FOR LOWER AND HEARD ANOTHER XMISSION ON FREQ WHEN I FINISHED XMITTING. OBVIOUSLY I WAS BLOCKED. I ASKED FOR LOWER AGAIN AND NO REPLY. INTENSITY OF TURB INCREASED AS WE ENTERED THE VIRGA WITH THE ACFT BECOMING MORE UNCONTROLLABLE. I REDUCED PWR AND HELD AN APPROX FLAT ALT. I ANNOUNCED ON FREQ THAT I WAS LEAVING 11000 FT. ACFT DSNDED TO 10600 FT WHERE TURB INTENSITY REDUCED CONSIDERABLY. I AGAIN XMITTED TO APCH THAT 'I NEED A LOWER ALT.' HE IMMEDIATELY CAME BACK WITH 'I SEE YOU HAVE DSNDED;' AND CLRED ME TO 9000 FT. LATER; UNDER VECTORS THE CTLR ADMONISHED ME TO 'NEVER DO THAT AGAIN; YOU WERE RIGHT OVER THE DEP PATH WHERE ACFT ARE CLRED TO 10000 FT;' IE; ONLY A 1000 FT SEPARATION. I TOLD HIM I'D NEVER DONE ANYTHING LIKE THAT IN 30 YRS OF FLYING. I CALLED HIM ON THE GND; SPOKE TO HIS SUPVR AND LEARNED THAT THE CTLR WAS DISTRACTED BY 2 AIRPLANES AHEAD OF ME THAT WERE NOT FOLLOWING VECTORS DUE TO SIMILAR TURB ENCOUNTERS (OR EXPECTED ENCOUNTERS) AND A B727 HAD JUST BROKEN OFF ON FINAL APCH DUE TO HVY TURB AND LOW LEVEL WINDSHEAR WARNINGS. I EXPLAINED THAT I WAS VERY UNCOMFORTABLE ABOUT THE ALTDEV; THAT TCASII HAD SHOWN NO NEARBY TFC; AND THAT I WAS PREPARED TO DECLARE AN EMER IF ORDERED TO REGAIN 11000 FT IN THAT AREA. THE SUPVR HAD CHKED ALREADY AND TOLD ME THERE WAS NO TFC CONFLICT BUT THE POTENTIAL FOR TROUBLE WAS HIGH IN THAT EXACT AREA. WE ALL AGREED IT WAS A TROUBLING AND VEXING SIT WITH RAPIDLY DEVELOPING OVERLOAD FOR ATC. MY QUESTION IS; WHY CAN'T PLTS BE GIVEN AN 'ESCAPE RTE' ROUTINELY; DURING SEVERE WX OPS ON STAAR ARRS? SIDS HAVE LOST COM PROCS; OVERWATER AIRWAY RTES INCLUDE SPECIFIC PROCS FOR EXITING THE AIRWAY IN AN EMER (USUALLY ENG FAILURE).