MU300 CREW EXPERIENCES SEVERE TURB AT 16500 FT W OF IAH.

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DEPARTED IAH ON AN IFR FLT TO BAZ (NEW BRAUNFELS) THERE WERE NUMEROUS TSTMS N OF OUR LINE OF FLT; WHICH APPEARED THAT WE WOULD BE ABLE TO CIRCUMNAV. I PERSONALLY CHKED THE RADAR PRIOR TO THE DEP AND ALL OF THE TSTM ACTIVITY FOR OUR ENRTE PORTION OF FLT WAS WELL N OF OUR LINE OF FLT EXCEPT JUST E ON AUS (AUSTIN; TX); WHICH WE COULD NAV AROUND. THERE WERE SOME TSTMS DURING THE CLB PHASE BUT WERE CIRCUMNAVIGATEABLE. AFTER TKOF OUR CLB WAS TO A FINAL ALT OF FL200. DURING THE CLB WE REQUESTED SEVERAL HDG DEVS AS THE STORMS IN THE IMMEDIATE AREA WERE BUILDING RAPIDLY WITH THE APCHING FRONT BUT REMAINED TO THE R; N OF OUR COURSE. OUR CLB WAS ALL IN VMC CONDITIONS. THE CTLR CONTINUED TRYING TO GET US TO ACCEPT A CLRNC TO THE R; N OF OUR CURRENT COURSE WHICH WOULD HAVE PUT US IN A 35-40 KT PLUS TSTM. WE REFUSED THOSE REQUEST DUE TO THE STORMS THAT WE SAW VISUALLY. HE SAID HE COULD ONLY LEAVE US ON OUR CURRENT HDG FOR A 'LITTLE WHILE DUE TO ARR CONFLICTS.' ONCE REACHING THE FINAL ALT OF FL200 WE COULD SEE AROUND THE LAST TSTM TO OUR R; N OF OUR CURRENT COURSE. THE CTLR CONTINUED TO ASK IF WE COULD ACCEPT A TURN TO THE R AND WE CONTINUED TO SAY NO; BUT WE WOULD BE ABLE TO SHORTLY. ONCE WE COULD SEE CLR AROUND THE EXISTING STORM TO OUR R WE REQUESTED A HIGHER ALT OF FL240 AND COULD TURN R FOR HIM. THE TONE IN HIS VOICE SOUNDED VERY FRUSTRATED AND HE DECLINED OUR REQUEST AND TOLD US TO DSND TO 14000 FT. AT THAT TIME WE WERE ON TOP AND COULD SEE AROUND THE LARGE TSTM THAT WE WERE PASSING AND WE COULD GO MORE TO THE R NOW BUT WE DID NOT MAKE THAT REQUEST OR INFORM THE CTLR AS I STILL PREFERRED TO STAY ON OUR CURRENT HDG A LITTLE LONGER. WE BEGAN A 1000 FPM DSCNT AND WENT IMC AT APPROX FL180. AT ABOUT THAT TIME WE BEGAN EXPERIENCING SOME LIGHT TO MODERATE TURB BUT NOTHING OUT OF THE ORDINARY. THE CTLR THEN CLRED US DIRECT MARCS INTXN (30 DEGS R). WHEN WE PASSED THROUGH +/-16500 FT WE EXPERIENCED SEVERE TURB. I REDUCED THE THROTTLES TO FLT IDLE AND APPLIED THE SPD BRAKES TO MAINTAIN MANEUVERING SPD AND TURNED THE IGNITERS ON. THE ONLY KNOWN WX I HAD SEEN WAS N OF OUR LINE SO I TURNED APPROX 30-35 DEGS TO THE L; S. AFTER A MIN OR TWO; I MADE AN ANNOUNCEMENT ON THE CTR FREQ THAT WE WERE IN SEVERE TURB. THE CTLR ASKED IF THE ACFT WAS OK AND I REPLIED 'OK FOR NOW.' WE DID NOT REQUEST A DEVIATION FROM CTR AS WE WERE BUSY AT THE TIME AND I HAD MADE AN ANNOUNCEMENT OF OUR PROB. IN ADDITION WE BEGAN TO PICK UP SOME ICING. THE TURB SLOWED FOR 30 TO 40 SECONDS AND BEGAN AGAIN FOR ANOTHER COUPLE OF MINUTES. WHEN WE CAME OUT OF IMC WE TOLD THE CTLRS 'WE WERE OUT OF IT' AND THEY ASKED WHAT HEADING WE WERE ON AND WE INFORMED THEM. THEY THEN ASSIGNED US A 240 DEG (THAT'S THE HEADING IF I REMEMBER) HEADING WAS STILL S OF OUR COURSE AND WE WERE IN VMC CONDITIONS AT 14000 FT. WE WERE THEN GIVEN A COUPLE OF DESCENT CLRNCS AND THEN CLRED DIRECT TO OUR DEST. AFTER MUCH RESEARCH ON THE INTERNET AND SEVERAL DISCUSSIONS WITH OTHER PLT'S; WE EXPERIENCED THIS SEVERE TURB AS A RESULT OF WINDSHEAR ASSOCIATED WITH THE FAST MOVING COLD FRONT. MY CONCERN IS THAT THE CTLR BECAME AGITATED AND MAY HAVE TRIED TO VIOLATE ME AS A RESULT OF HE HEADING/ALT DEVS. I TOOK THE CORRECTIVE ACTION I DEEMED NECESSARY SAFETY OF THE FLT.