AN ACR TAXIED ONTO AN ACTIVE RWY; CITING POOR VISIBILITY; SNOW COVERED SIGNS; AND FAILURE TO OBSERVE STERILE COCKPIT RULE; AS CONTRIBUTING FACTORS.

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AFTER DE-ICING; WE EXITED THE RAMP IN THE VICINITY OF THE GATE; TAXIING WBOUND TO JOIN RWY 05R PARALLEL TXWY. AT THIS JUNCTION; RWY 18 ALSO INTERSECTS AT ABOUT THE SAME LOCATION; SO NOT A GOOD PLACE FOR SIGNAGE. WE INADVERTENTLY TAXIED ONTO RWY 05R; GND CTLR INFORMED US OF OUR INCURSION; AND WE TAXIED CLR; AS DEP TFC ROLLED DOWN THE RWY. VISIBILITY WAS SOMEWHAT HAMPERED BY LIGHT SNOW; AND DE-ICE FLUID FLOWING DOWN WINDSHIELD. FO HAPPENED TO MENTION FINDING HIS WALLET THAT HE LEFT ON A PREVIOUS ACFT (STERILE COCKPIT); AND DESPITE MY BEST EFFORTS; I WAS REELING FROM A LAST-MIN-RIDE FROM THE HOTEL. OTHERWISE THE TAXI RTING IS FAMILIAR TO ME AND WE SHOULD NOT HAVE MADE THIS ERROR. I THANKED THE GND CTLR WHO REALLY SAVED THE DAY! CORRECTIVE ACTION: ADVANCE PLANNING TO AVOID CREW TRANSPORT PROBS. MAINTAIN AND ENFORCE STERILE COCKPIT. MORE HELP FROM FO DURING TAXI; AND SIMPLY; DO NOT TAXI ONTO ACTIVE RWYS! SUPPLEMENTAL INFO FROM ACN 297688: AN 'MD-80' WAS TAKING OFF ON RWY 05R AT THE TIME. CAPT WAS TAXIING. ALL MARKINGS WERE OBSCURED BY SNOW AND ICE. TWR RPTED VISIBILITY OF 1 1/2 MI IN SNOW; AND BLOWING SNOW; AND FOG. WE WERE BACK ON 'L' WHEN THE DEPARTING FLT PASSED.