What causes fog to form?

Fog forms when warm, moist air cools rapidly, causing water vapour to condense into tiny water droplets suspended in the air. This often occurs when the air temperature drops to the dew point. Common types of fog include radiation fog, which forms on clear nights when the ground cools quickly, and advection fog, which occurs when warm air moves over a cooler surface. Fog reduces visibility, creating unique atmospheric conditions but also posing challenges for transportation.