A CAPT BRIEFED THE FMS VISUAL INTO SFO AND HAD BEEN CLRED TO A FIX ON THE APCH. MEANWHILE; A NEW ATIS WAS ISSUED AND THE CAPT DID NOT NOTICE THE REDUCTION IN VISIBILITY WHICH PRECLUDED THE USE OF THIS PARTICULAR APCH.

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THE COPLT AND I BRIEFED THE FMS VISUAL APCH RWY 28R FOR SAN FRANCISCO. WE NOTED ON THE ATIS THAT SFO VISIBILITY WAS 5 MI. THIS APCH REQUIRES 5 MI OF VISIBILITY AND A 2100 FT CEILING. (THERE WAS NO CEILING RPTED ON THE ATIS.) AS WE NEARED TRDOW INTXN (A FIX ON THE FMS VISUAL APCH ON THE SFO 095 DEG RADIAL 19 DME); WE WERE ASKED IF WE HAD THE NEW ATIS INFO. THE COPLT AND I OBTAINED ATIS INFO AND INFORMED BAY APCH. WE WERE THEN CLRED FOR THE FMS BRIDGE VISUAL APCH TO RWY 28R IN SFO. OUR FLT LANDED ON RWY 28R WITHOUT INCIDENT AND WE TAXIED TO THE GATE. AFTER WE COMPLETED THE PARKING CHKLIST; I HAPPENED TO NOTICE THAT THE VISIBILITY ON THE NEW ATIS HAD DECREASED TO 4 MI. WE FLEW THE FMS BRIDGE VISUAL APCH WITH INADEQUATE RPTED VISIBILITY. THE FACTORS THAT AFFECTED THIS ERROR: 1) APCH EXPECTANCY. WE HAD BRIEFED THE FMS VISUAL APCH AND HAD BEEN CLRED TO TRDOW INTXN (A PUBLISHED FIX ON THE APCH PATH RWY 28R). 2) WHEN FLYING A 'VISUAL APCH' WE DON'T INCORPORATE VISIBILITY REQUIREMENTS INTO OUR MIND SET. AFTER ALL; IT IS A 'VISUAL APCH.' 3) NOT PAYING CLOSE ENOUGH ATTN TO NEW ATIS INFO. WE MISSED THE REDUCTION IN VISIBILITY.