Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 150; Flight Crew Total 11500; Flight Crew Type 5000
Ground Event / Encounter Loss Of Aircraft Control; Ground Event / Encounter Weather / Turbulence; Ground Excursion Taxiway
Aircraft Aircraft Damaged; General Evacuated
Weather
On taxi out to Runway 34 at BGM airport there was blowing snow bringing the visibility down to almost 0. The only taxiway sign for taxiway L (Lima) was obscured. The yellow directional markings on ground were covered with snow. We missed the taxiway and slid off ramp just west of taxiway Lima(L). No injuries but substantial damage to nose gear.
Began taxi from ramp between Taxiways M and L.  While taxiing parallel to Bravo PF (pilot flying) called for taxi checklist.  PM (pilot monitoring) head was down for a brief period while doing taxi checks.  When PM looked up he told PF that something looked wrong about the aircraft position.  Almost immediately the aircraft entered the grass on the east side of Lima.  PF attempted to continue through grass to Bravo and the Aircraft dropped into a snow obscured swale and came to a stop.  Aircraft secured and evacuated.  2 crew and 2 passengers on board.  No injuries.
Flight crew reported excursion from taxiway during low visibility conditions on snow-covered taxiway BGM airport.