BE58 PLT DEVIATED FROM ASSIGNED ATC HDG TO AVOID TSTM CELLS PAINTED ON THE ACFT WX RADAR.

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DEPARTED JBR IFR CLRED DIRECT DAL (HDG 240 DEGS) 2000 FT. AFTER LIFTOFF FROM RWY 5; I TURNED L. IN MY TURN; FSS ADVISED ME OF DEVELOPING STORMS SW OF JBR AND RECOMMENDED SE DEP FOR 10-15 MI BEFORE TURNING ON COURSE. I QUESTIONED THIS; AS IT MADE MORE SENSE TO ME TO GO W THEN TURN SW ON COURSE AFTER PAST STORMS. FSS BRIEFER AGAIN SAID SE DEP IS BEST OPTION. SINCE HE HAD MORE INFO THAN I; I DECIDED HIS RECOMMENDATION IS BEST CHOICE. (ALSO BRIEFERS HAVE ALWAYS BEEN RELIABLE TO ME IN THE PAST.) I THEN TURNED R TO 240 DEGS AND IN MY TURN CHKED IN WITH CTR AND REQUESTED 150 DEG HDG. I WAS LEVELING OFF AT 2000 FT THEN ALSO. CTR DID NOT CARE FOR THIS BECAUSE OF MEM CLASS B APCH AIRSPACE. I EXPLAINED WHY I WANTED 150 DEGS. HE ASKED MY LOCATION AND I TOLD HIM 7 MI S OF JBR VOR (I ACTUALLY WAS 7.2 MI ON 200 DEG RADIAL). HE LET ME GO A SHORT DISTANCE ON 150 DEG HDG (I STOPPED ON 150 DEGS ON MY R TURN TO 240 DEGS). HE THEN WANTED ME TO GO TO 240 DEGS; SO I DID. THIS PUT ME RIGHT IN DEVELOPING STORMS. CONTINUOUS MODERATE TURB (OCCASIONALLY SEVERE). MY RADAR SHOWED MULTIPLE INTENSE AREAS. THE STRONGEST RETURNS WERE DIRECTLY IN FRONT OF ME. I ALSO HAD SEVERAL INTENSE ECHOES OFF TO MY L AND ONE TO MY R. I WAS LEVEL AT 3000 FT BY NOW (I BELIEVE) AND ATC WAS STILL NOT PICKING UP MY XPONDER. THE FREQ WAS VERY BUSY AND I COULDN'T FIND A GOOD BREAK TO REQUEST A TURN TO THE R. I TURNED R TO TRY TO AVOID THE LARGEST RETURNS AND PLANNED ON JUST MOVING R APPROX 2 MI. AT THAT POINT I WAS HDG APPROX 270 DEGS BOUNCING STRONGLY FROM 260-280 DEGS (LOTS OF YAW). THE CTLR ASKED MY HDG AND I TOLD HIM. HE WAS QUITE UPSET AND TOLD ME THAT I CAN'T JUST FLY ANYWHERE I WANT TO. I TRIED TO EXPLAIN THE SIT BRIEFLY. THEN I WAS INSTRUCTED TO CLB. THEY PICKED UP MY XPONDER AND THE REST OF THE TRIP WAS UNEVENTFUL. PROB: I TURNED R; OFF OF ASSIGNED VECTOR WITHOUT CTR'S APPROVAL. STRESSORS FOR ME: CONTINUOUS MODERATE TURB (OCCASIONALLY SEVERE). IMC; DME OFF JBR VOR WAS NOT WORKING ( I USED GPS). FEAR OF GOING INTO DEVELOPING STORMS. STRESSED THAT CTLR WAS UPSET WITH ME BECAUSE OF 150 DEG HDG. FEAR OF LOSS OF CTL. I LOST ANR AT LIFTOFF (VERY NOISY). STRESSORS FOR CTLR: NOT KNOWING EXACTLY WHERE I WAS (NO XPONDER RETURN). AFRAID I WOULD APCH MEM'S APCH AIRSPACE. FELT I WAS RENEGADE PLT (WENT TO 270 DEGS WITHOUT PERMISSION). I BELIEVE THERE WAS AN ACFT APCHING JBR FROM E (4000 FT). BUSY FREQ. IF I HAD TO DO IT AGAIN: TURN L AFTER LIFTOFF TO 240 DEGS AS PLANNED AND ASK ZME FOR VECTORS W OR NW TO AVOID DEVELOPING STORMS. BE MORE ASSERTIVE IN REQUESTING HDG CHANGE.