Answer:

fogs

AnswerCrossword Clue
FOGSMistifies?
FOGSClouds (up)
FOGSThey're hard to see through
FOGSSteams (up)
FOGSMuddles
FOGSObscures
FOGSFrequent San Francisco conditions
FOGSReasons for lighthouses
FOGSHeavy mists
FOGSAirport dangers