A300
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown; Ground Excursion Taxiway; Ground Incursion Taxiway
General None Reported / Taken
Human Factors; Weather
Weather was bad (snow and very low visibility). Taxied Air Carrier X via Delta and Delta Two and cross Runway 23L. I forgot that Delta Two was closed because it wasn't plowed. Air Carrier X slid off the taxiway into the grass at Delta two. He didn't know if he was past the hold short lines; so we closed the runway. Had to get a tow to get him off the grass. I just forgot that Delta two was closed. It's a common taxiway that we use during the Air Carrier outbound push and I reverted to old habits.
Tower Controller described a taxiway excursion when an air carrier was cleared via a closed taxiway during snow and very low visibility conditions.