When does radiation fog typically form?

Radiation fog typically forms on clear nights with very gentle winds due to the process of radiational cooling. As temperatures drop during the night, the ground loses heat quickly, which in turn cools the air layer directly above it. If the air becomes sufficiently cool and the relative humidity reaches saturation, condensation occurs, leading to the formation of fog. Clear skies are essential because they allow for maximum heat loss from the surface. A gentle wind helps prevent the mixing of the air layers, allowing the cooling effect to dominate near the ground.

Other conditions, such as windy days, high humidity during the day, or rising afternoon temperatures, do not support the formation of radiation fog. Wind would disrupt the temperature inversion necessary for fog formation, while high daytime temperatures typically increase evaporation rather than cooling, and thus, fog is less likely to occur.