MLG TAXIING IN BLOWING SNOW ENTERS RWY IN ERROR.

Narrative

THE TRANSITION TO CHICAGO AIRSPACE WAS PUNCTUATED BY SPD CHANGES; HOLDING INSTRUCTIONS; A CANCELED HOLD AND VECTORS. AN INTERCEPT HDG AND ALT WERE ISSUED FOR ILS 14R AT ORD. THE WX WAS RPTED SOMETHING LIKE 300 FT OVCST. 2200 RVR (APCH) WITH DECREASING VALUES AT MIDPOINT AND ROLLOUT. WINDS WERE 110 DEGS AT APPROX 10 KTS. WE BRIEFED A LOW APCH AND THE CAPT MADE A NORMAL LNDG. VISIBILITY WAS VERY POOR ON ROLLOUT. AFTER LNDG THE TWR REQUESTED WE EXIT ON T6 OR T7. WE ELECTED T7 AND VERY CAUTIOUSLY TURNED OFF THERE. GND THEN INSTRUCTED US TO TURN R ON TXWY TANGO. AT THIS POINT; BLOWING SNOW REDUCED VISIBILITY FURTHER AND WE MOVED FORWARD WITH EXTREME CARE UNTIL SPOTTING TXWY LIGHT STANCHIONS AT OUR 2 O'CLOCK POS. WE PROCEEDED DOWN WHAT WE BELIEVED WAS TXWY T; VIRTUALLY 1 LIGHT AT A TIME; WITH GREAT ATTN TO MAINTAINING OUR TRACK ON A PAVED SURFACE. AFTER A SHORT DISTANCE; THE CAPT SENSED WE MIGHT BE IN THE WRONG PLACE. HE TURNED L IMMEDIATELY; INFORMING GND THAT HE SUSPECTED WE MIGHT BE ON A RWY. POS WAS THEN RE-ESTABLISHED AND REMAINDER OF TAXI TO RAMP AREA COORDINATED WITH GND. PARTIALLY TO WHOLLY OBSCURED SIGNAGE AND NEAR WHITE-OUT CONDITIONS MADE TAXI DIFFICULT. CAPT'S WIPER BLADE BECAME INOP. SUPPLEMENTAL INFO FROM ACN 264507: USING TXWY LIGHTS FOR GUIDANCE; VISIBILITY EXTREMELY POOR. PASSING WDB ON PARALLEL TXWY BRAVO WITH 15 KT WIND FROM THE E CREATED VIRTUAL WHITE-OUT.