LTSS -- WX FACTORS -- WHILE MANEUVERING AROUND WX AN ACR RECEIVES A TCASII 'RA' CAUSING IT TO DIVE BELOW OTHER TFC.

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FLT DEPARTED ATL IN VFR CONDITIONS WITH CAPT AT THE CTLS. WE WERE CLRED VIA THE ATLANTA 4 DEP TO EAONE FIX; THEN AS FILED. FLT WAS ORIGINALLY CLRED TO 10000 FT AS PER THE SID AND THEN SUBSEQUENTLY TO 12000 FT AND 13000 FT. WE REQUESTED DEV FROM AN ASSIGNED 060 DEG HDG TO AVOID WX. CLRNC WAS RECEIVED TO DEVIATE TO THE R. AFTER SEVERAL MINS ON AN APPROX E HDG; CTLR ADVISED THAT WE COULD RECEIVE A HIGHER ALT IF WE COULD ACCEPT A N TURN. AFTER CHKING WX BOTH VISUALLY AND WITH RADAR; WE ADVISED THAT WE COULD ACCEPT A L (N) TURN. CTLR CLRED US TO TURN L AND PROCEEDED 'DIRECT GSO WHEN ABLE.' AS OUR HDG CAME TOWARD A DIRECT COURSE TO GSO; IT BECAME APPARENT THAT A PREVIOUSLY UNSEEN BUILDUP LAY AHEAD. WE CONTINUED OUR L TURN UNTIL CLR OF THIS BUILDUP AND THEN BEGAN A TURN BACK TOWARD GSO. IN ABOUT THIS SAME TIME FRAME -- TCASII ANNUNCIATED A RA -- TO WHICH WE RESPONDED WITH EVASIVE ACTION. (WE BELIEVE THAT THE SUM OF OUR DEVS (L AND R) LAY E OF OUR ORIGINAL VECTOR OF 060 DEGS). TFC WAS SPOTTED VISUALLY DURING OUR EVASIVE MANEUVER AND WAS APPARENTLY ALSO TRACKING IN A NE DIRECTION; ALSO AT 13000 FT. CTLR ADVISED US OF OUR CONFLICT AFTER TCASII HAD SOUNDED AND AFTER WE HAD ALREADY BEGUN OUR EVASIVE ACTION. SHE TOLD US TO MAINTAIN OUR NEW ALT (NOW 12500 FT) AND SHORTLY THEREAFTER; WE WERE CLRED DIRECT TO GSO AND GIVEN A CLB. CONTRIBUTING FACTORS: NORMAL SEQUENCE OF ALTS ON DEPARTING ATLANTA ARE 10000 FT; 14000 FT; AND FL230. SOMEHOW WE GOT HELD DOWN AT 13000 FT ALONG WITH ANOTHER ACFT. ANOTHER ACFT ON FREQ MADE REPEATED REQUESTS FOR HIGHER ALT; CONCERNED THAT HE MIGHT BE 'UNABLE TO MAKE HIS DEST.' NOT SURE IF THIS WAS OUR CONFLICT ACFT. THERE WAS NO ADVISORY GIVEN (EARLY ON) OF THE OTHER ACFT AT THE SAME ALT WHEN WE RECEIVED OUR L TURN CLRNC. NO LIMIT (SUCH AS 'NOT BEYOND HDG 060 DEGS') WAS PLACED ON OUR L TURN. ALSO; CLRNC WAS STATED AS 'DIRECT GSO; WHEN ABLE.' HAD WE BEEN ADVISED OF OUR TFC AND AWARE THAT OUR CLB CLRNC WOULD BE DELAYED; WE MIGHT NOT HAVE ACCEPTED THE L TURN CLRNC.