What type of fog typically forms under clear night skies?

Radiation fog typically forms during clear night skies when the ground loses heat through radiation. As the surface cools down, the air directly above it can also cool to the dew point, leading to condensation and the formation of fog. This process is most effective under clear skies because clouds act as a blanket, trapping heat and preventing the ground from cooling sufficiently.

Conversely, other types of fog have different formation mechanisms. Advection fog occurs when warm, moist air moves over a cooler surface, causing the moisture to condense. Upslope fog is formed when air is lifted along a terrain slope and cools adiabatically, and evaporation fog forms when water vapor is added to the air, causing it to reach saturation. Both of these processes do not rely on the clear night sky conditions that are critical to the formation of radiation fog.