CAPT AND DISPATCHER NAME BFI AS AN ALTERNATE FOR ACFT INBOUND TO SEA. FAIL TO NOTE THE INTENDED; LONGER; RWY IS NOTAMED CLOSED.

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ACCEPTED UNSUITABLE ALTERNATE ON DISPATCH RELEASE. THE WX FORECAST IN SEATTLE DID NOT REQUIRE AN ALTERNATE. THE OBSERVATION AT XA53 IN SEATTLE WAS AS FOLLOWS: 5 MILES VIS IN MIST WITH SCATTERED CLOUDS AT 100 FT AND OVERCAST AT 4000 FT. BFI WAS LISTED AS ALTERNATE 1. I CHECKED THE WX; WHICH WAS ADEQUATE FOR AN ALTERNATE. I GLANCED AT THE NOTAMS; HOWEVER; I MISSED THE NOTAM STATING THAT BFI'S LONG RWY WAS CLOSED. DURING THE FLT TO SEATTLE I RECHECKED THE NOTAMS; AND NOTED THE NOTAM STATING THAT THE LONG RWY WAS CLOSED. I COULD NOT CONFIRM OUR ABILITY TO USE THE SHORT RWY; SO I CALLED DISPATCH. WE DISCUSSED THE PERFORMANCE ISSUES; AND DISCUSSED OTHER ALTERNATES. FORTUNATELY; I CARRIED EXTRA FUEL; AND AFTER CHECKING THE WX; WE AMENDED THE RELEASE TO SHOW PAINE FIELD AS ALT 1. BY THE TIME WE LANDED AT SEA; THEY WERE CONDUCTING VISUAL APCHES. EVEN THOUGH AT NO TIME WAS AN ALTERNATE REQUIRED LEGALLY; MISSING THAT CRITICAL NOTAM DURING MY PREFLT CAUSED ME CONCERN. I WASN'T EXCEPTIONALLY TIRED DURING THIS PARTICULAR DAY. WE HAD FLOW BACK TO SEATTLE. WE WERE UNCERTAIN ABOUT OUR SLOT TIME; SO WE WERE HURRYING TO GET OUT ON TIME. THERE WERE APPROX 50 NOTAMS FOR SEA AND BFI; AND MULTIPLE PAGES OF FDC NOTAMS AND AREA WX. NOTAMS ARE ORGANIZED BY NUMBER AND NOT BY TYPE. THE PARTICULAR NOTAM OF RWY CLOSURE WAS ABOUT HALF WAY DOWN THE LIST. LACK OF ARPT DIAGRAMS AND INFORMATION: ALL THE BFI RWY INFORMATION IS IN THE BRICK.