ACS Weather Information Practice Exam

Radiation fog forms under specific atmospheric conditions that are most prevalent at night or in the early morning, making it unique among the types of fog listed. This type of fog develops when the ground loses heat through radiation, causing the air near the surface to cool rapidly. When the temperature of the air drops to its dew point, water vapor condenses into tiny water droplets, resulting in fog.

Typically, radiation fog is enhanced by clear skies and calm winds, which facilitate the cooling process. Because this phenomenon relies on nighttime cooling and the absence of sunlight, it predominantly occurs during the night or just before dawn.

The other types of fog, such as advection fog, occurs when warm, moist air moves over a cooler surface and loses heat, which can happen at any time, not just at night. Upslope fog forms as moist air rises along topographical features, and frontal fog develops as warm air is forced to rise over a cold front, neither of which are limited to the nighttime or early morning hours.