A300
Workload; Time Pressure; Situational Awareness
Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Requested ATC Assistance / Clarification; General Declared Emergency; General Maintenance Action
Aircraft; Weather
40 miles from our destination at 12000 feet in descent received Avionics Smoke Alarm.  Declared emergency and landed Runway 06R. Avionics Smoke Alarm activated in my opinion due to water/melted snow that entered aircraft while on ground loading at flight origin.The ground crew did a good job of removing snow off the cans but in blizzard conditions with high winds and blowing snow it is near impossible to keep all snow out of the aircraft.
Avionics smoke indication about 45 miles south of destination around 12;000 feet; approaching level off at 10;000 feet. We [advised ATC] and landed at our filed destination. We told Approach Control we would keep our airspeed above 250 KIAS below 10;000 feet in order to expedite our arrival.
An A300 Avionics Smoke alarm alerted descending through 12;000 feet about 40 miles from the destination; so an expedited descent and landing were accomplished. The cause may have been cabin moisture from the previous destination.