AN ACR PILOT RPTS A DSNDING RA WHILE IMC AT 2000 FT ON AN ILS APCH. ATC DID NOT CALL TFC AND CREW DID NOT DSND BECAUSE OF TERRAIN AND LOWER CLOUDS.

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WE WERE GETTING VECTORS TO FINAL APCH FOR ZZZ RWY 7R. THE INITIAL HDG WAS A DOGLEG HDG FROM THE S. WE WERE GIVEN A DSCNT TO 2000 FT. AS WE NEARED THE FINAL COURSE; APCH INFORMED US THAT WE WOULD BE VECTORED ACROSS FINAL FOR SPACING. (IN THE END IT APPEARED THAT THERE WAS A LIGHT ACFT FIT IN THE APCH LINE.) AFTER XING FINAL; WE RECEIVED A TURN TO INTERCEPT THE LOC FROM THE N. WE INTERCEPTED AT APPROX 30 MI WHILE STILL IN THE DSCNT. AFTER INTERCEPTING THE LOC AND LEVELING AT 2000 FT; WE RECEIVED A TCAS TA OF TFC 100 FT BELOW; AT 1 MI IN OUR 10 O'CLOCK POS. THE TFC APPEARED TO BE CLOSING ON OUR POS. AT THIS POINT WE WERE ABOUT 20 DME (15 MI FROM ABC). I WAS ABOUT TO TAKE EMER ACTION AND BREAK OFF THE APCH TO THE S WHEN WE CAME OUT OF THE CLOUDS. THE FO AND THE RELIEF PLT BOTH SPOTTED THE TFC. I LOOKED AND SPOTTED THE DESCRIBED ACFT ALSO. IT WAS AT OUR ALT HEADING STRAIGHT FOR US. WE THEN RECEIVED AN RA TO DSND AT 500 FPM. THE ACFT BROKE TO THE R (W). I HAD THE ACFT IN SIGHT AND WAS HESITANT TO DSND INTO THE CLOUDS. THE RA WENT AWAY A MOMENT LATER AND WE RE-ENTERED THE CLOUDS. THE FO INFORMED APCH CTL OF THE ACFT DESCRIPTION AND LAST KNOWN POS/HDG. THE REST OF THE APCH WAS CONTINUED WITHOUT INCIDENT.