Final answer:
Upslope fog is formed when moist air is forced to rise up a sloping terrain. Three necessary conditions for its formation are moist air, upslope movement, and a stable atmosphere.
Step-by-step explanation:
Upslope fog is formed when moist air is forced to rise up a sloping terrain, such as a mountain. The process involves several necessary conditions Moist air There must be enough moisture present in the air for fog to form. This can come from evaporation over bodies of water or from advection, where moist air is transported into the area Upslope movement The air must be forced to rise up a sloping surface. As the air ascends, it cools and reaches its dew point, leading to condensation and the formation of fog.Stable atmosphere A stable atmosphere is necessary to inhibit vertical mixing and promote the adiabatic cooling that creates fog. Inversions, where a layer of warm air sits above a layer of cooler air, can help maintain stability.