What type of fog forms in low lying areas, especially in mountain valleys?

Radiation fog forms in low-lying areas, particularly in mountain valleys, due to the cooling of the ground at night. During the night, the Earth's surface loses heat through radiation, which cools the air close to the surface. When the air temperature drops to the dew point in these areas, water vapor condenses into tiny droplets, creating fog. This phenomenon is most common in valleys where cold air can settle and where the nighttime cooling can be particularly effective, resulting in very foggy conditions. The presence of moisture in the air and clear skies typically enhances the formation of radiation fog since clouds would trap heat and inhibit the cooling needed for fog formation.

Advection fog generally forms when warm, moist air moves over a cooler surface, causing the air near the surface to cool and condense. Steam fog occurs when cold air moves over a warm body of water, creating fog where the warm water evaporates and cools quickly. Upslope fog arises as moist air is lifted over mountain terrain, cooling as it rises, but it is less specific to low-lying areas and valleys compared to radiation fog.