IN HAZY AND DARK CONDITIONS; A B737 FLC DID NOT COMPLY WITH AN ATC CLRNC DUE TO VISUAL OBSERVATION OF THE TFC AND TCASII INFO. WHEN THE JETSTREAM BEGAN A VISUAL SEPARATION DSCNT; THE FLC TOOK EVASIVE ACTION TO AVOID THE ACFT AND RECEIVED A TCASII RA TO CLB.

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WE DEPARTED RICHMOND ON THE WAY TO CHICAGO; CLBING OUT ON THE 264 DEG RADIAL OFF THE RICHMOND VOR AT ABOUT 25 DME. WE WERE LEVEL AT 16000 FT WAITING FOR CLRNC TO CLB HIGHER. FLT CONDITIONS WERE DARK AND HAZY; AND WE WERE IN BETWEEN LAYERS. WASHINGTON CTR (ATC) ADVISED US OF TFC; A JETSTREAM AT OUR 10 O'CLOCK POS; AT 17000 FT AND 15 MI. IMMEDIATELY FOLLOWING THAT; WE HEARD ATC ADVISE THE OTHER ACFT OF A BOEING 737 AT THEIR 2 O'CLOCK POS; AT 16000 FT AND 15 MI. THE JETSTREAM ADVISED ATC THAT THEY HAD (OUR) ACFT INSIGHT. ATC SUBSEQUENTLY GAVE THE JETSTREAM A CLRNC TO DSND TO 15000 FT AND TO MAINTAIN VISUAL SEPARATION FROM US. ATC THEN CLRED US TO 19000 FT AND ADVISED US THAT THE OTHER ACFT WOULD BE MAINTAINING VISUAL SEPEPARATION FROM US. THE FO AND I OBSERVED THE OTHER ACFT VISUALLY AND ON TCASII; AND DECIDED TO MAINTAIN OUR PRESENT ALT OF 16000 FT. WE THEN OBSERVED ON TCASII THE OTHER ACFT STARTING A DSCNT. OUR TCASII TARGET CHANGED FROM WHITE TO YELLOW AND INDICATED A DSCNT OF LESS THAN A 1000 FT SEPARATION FROM OUR ACFT. WITH BOTH A VISUAL AND TCASII CONFIRMATION OF A COLLISION COURSE; WE INITIATED A L TURN ATTEMPTING TO PASS BEHIND THE ACFT. AT THIS TIME THE TCASII SOUNDED; 'TFC; TFC; CLB; CLB;' AND THE VSI INDICATED A COMPLETE RED ARC EXCEPT FOR A 1500 TO 2000 FT GREEN BAND. AT THIS POINT WE ATTEMPTED TO INITIATE THE CLB WHEN THE OTHER ACFT WENT OVER TOP OF US.