Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Problem:Passage: Advection fog is famous in San Francisco, California. Warm, moist air comes in from the Pacific Ocean. The air blows over the cold California current. When the air cools below its dew point, fog forms. Sea breezes bring the fog onshore. Answer: fog
Solution:
What forms after air cools below its dew point?