A320 CREW CROSSED THE RWY HOLD SHORT LINE AT MEM; AT NIGHT; IN THE RAIN; IN LOW VISIBILITY CONDITIONS.

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ACFT STOPPED HALFWAY OVER HOLD SHORT LINE (WINGS ON HOLD SHORT LINE) DURING TAXI FOR TKOF ON RWY 35 AT MEM. WE CROSSED OVER THE HOLD SHORT LINE BY 1/2 OF ACFT LENGTH. SEVERAL FACTORS INVOLVED. MAJOR FACTOR: POOR VISIBILITY AT NIGHT; RAIN; AND WET TXWY MADE SITUATIONAL AWARENESS VERY DIFFICULT. THE NEXT DAY; A BEAUTIFUL SUNNY DAY; IT WOULD HAVE BEEN IMPOSSIBLE FOR US TO MAKE THIS MISTAKE AS WE ONCE AGAIN TAXIED TO RWY 35 AND THE ENTIRE RWY ENVIRONMENT WAS CLRLY VISIBLE IN ALL DIRECTIONS. ANOTHER FACTOR WAS THE NEW TEMPORARY RWY 35 WITH THE HOLD SHORT LINE ON THE PARALLEL TXWY. WE STARTED OUR TAXI TO RWY 35C; BUT CHANGED TO RWY 35 DUE TO LENGTHY DELAYS FOR RWY 35C. RWY 35 WAS NOT BEING USED FOR ARRS SO DEPS WERE ONE RIGHT AFTER THE OTHER WITH LITTLE OR NO DELAYS BTWN THEM. ALTHOUGH I WAS AWARE OF THE HOLD POINT; OLD HABIT PATTERNS MADE ME FORGET THE HOLD POINT FOR RWY 35 AND I WAS GOING TO THE FAMILIAR HOLD POINT FOR RWY 36L. I SAW THE HOLD SHORT POINT BEFORE XING BUT 'KNOWING' THE HOLD SHORT LINE WAS AT THE LIGHTED RWY SIGNS AND PERPENDICULAR TO THE RWY; MY MIND SAID 'ILS HOLD.' JUST AS WE STARTED ACROSS THE LINE; I REALIZED MY MISTAKE AND BROUGHT THE ACFT TO A STOP. I WAS ALSO SCANNING WITH THE RADAR FOR WX ON DEP; AN ADDITIONAL DISTRACTION. NO TFC CONFLICT INVOLVED AS THE RWY WAS NOT BEING USED FOR ARRS; AND WE WERE CLRED INTO POS ABOUT 15 SECONDS AFTER COMING TO A STOP. GIVEN THE WX; I DOUBT ANYONE BUT US WERE AWARE OF OUR MISTAKE; BUT WE WERE SURE REMINDED THAT ALL PHASES OF FLT CAN BE HAZARDOUS AND REQUIRE CONSTANT REVIEW.