B737 ng flight crew reported that poor visibility and lack of signage caused a taxiway incursion.

Attributes
ACN	1696069
Time
Date	201910
Place
Locale Reference	MDW.Airport
State Reference	IL
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 191 Flight Crew Type 191
Events
Anomaly	Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Ground Incursion Taxiway

Narrative:

ATIS information bravo current with visibility at 2.5 miles and ceiling broken at 600 ft; wet runway with rain. We were cleared 'line up and wait runway 4R' following a departing aircraft with landing traffic on final. As soon as we stopped in position; tower instructed us to exit the runway at taxiway victor for landing traffic de-confliction. Taxiway victor; while marked on the airport diagram; is not marked on the airfield when approached from the runway 4R approach end. There is no sign. This caused confusion so we taxied past victor to the Y2 taxiway and exited the runway. Due to rain; we could not see the taxiway Y2 sign until we were past the unmarked taxiway victor. Taxi speed was appropriate for wet field conditions. ATC directed landing traffic to go-around. We were clear of the runway prior to the landing aircraft crossing the field boundary. We were subsequently cleared for takeoff.

Original NASA ASRS Text

Title: B737 NG flight crew reported that poor visibility and lack of signage caused a taxiway incursion.

Narrative: ATIS information Bravo current with visibility at 2.5 miles and ceiling broken at 600 ft; wet runway with rain. We were cleared 'line up and wait Runway 4R' following a departing aircraft with landing traffic on final. As soon as we stopped in position; Tower instructed us to exit the runway at Taxiway Victor for landing traffic de-confliction. Taxiway Victor; while marked on the airport diagram; is not marked on the airfield when approached from the Runway 4R Approach end. There is no sign. This caused confusion so we taxied past Victor to the Y2 Taxiway and exited the Runway. Due to rain; we could not see the Taxiway Y2 sign until we were past the unmarked Taxiway Victor. Taxi speed was appropriate for wet field conditions. ATC directed landing traffic to go-around. We were clear of the runway prior to the landing aircraft crossing the field boundary. We were subsequently cleared for takeoff.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.