A CAPT EXECUTED A GAR FROM A CHARTED VISUAL APCH; CITING LESS THAN ADVERTISED VISIBILITY; AND DIVISION OF ATTN DIFFICULTIES; AS CONTRIBUTING TO THE VISUAL LOSS OF THE RWY.

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RIVER VISUAL APCH TO RWY 18. PF OVERLOAD RESULTED IN OVERSHOOT OF TURN TO FINAL. BRIGHT MORNING SUN; AND FOG OVER THE RIVER; COMBINED TO REDUCE INFLT VISIBILITY BELOW 'ADVERTISED' VALUE. THIS MADE THE RIVER MORE DIFFICULT THAN NORMAL. I WAS CONCENTRATING ON REFERENCING THE E BANK OF THE RIVER WHILE XCHKING DME VERSES ALT. AS A RESULT OF MY 'INSIDE' CHKS; MY 'OUTSIDE' SCAN WAS IMPAIRED; EVEN MORE THAN IT HAD BEEN; BY THE MARGINAL VISIBILITY. AS A RESULT; I 'LET GO' OF THE RWY WHILE ENSURING THAT I DIDN'T PENETRATE PROHIBITED AREAS P-56. I DIDN'T IMMEDIATELY REACQUIRE THE RWY; VISUALLY; IN TIME TO EXECUTE A NORMAL TURN TO FINAL. THE RESULT: THE ACFT WAS OUT OF POS FOR A NORMAL LNDG. I ELECTED TO GAR; RATHER THAN ATTEMPT TO LAND. WHILE THIS DOESN'T QUALIFY AS AN 'INCIDENT;' IT HIGHLIGHTS THE DIFFICULTY IN FLYING CHARTED VISUAL APCHS; IN LESS THAN IDEAL VISIBILITY. ADDITIONALLY; RECENT COMPANY EMPHASIS ON STANDARDIZED CALLOUTS DEPRIVED ME OF ADDITIONAL HELP FROM THE PNF. OUR CURRENT POLICY CALLS FOR STANDARD CALLOUTS AND PROHIBITS NON-STANDARD OR 'COMFORT' CALLOUTS. I COULD HAVE USED A 'COMFORT CALLOUT' OF ALT AND DME EVERY 100 FT BELOW 1000 FT AGL; SO I COULD HAVE CONCENTRATED MORE ON OUTSIDE CUES. IN THE FUTURE; I WILL USE MY 'CAPT'S AUTH' TO REQUEST ADDITIONAL CALLOUTS; WHEN I THINK THEY MIGHT BE BENEFICIAL.