Which type of fog occurs when moist air is pushed up a hillside?

Upslope fog forms as moist air is lifted along a slope, such as a hillside or mountain. As the air ascends, it expands and cools due to lower pressure at higher altitudes. When the air cools to its dew point, condensation occurs, resulting in fog. This type of fog is particularly common in mountainous regions where moist air interacts with varying terrain.

Understanding this phenomenon is crucial for pilots, as flying through upslope fog can significantly reduce visibility, impacting flight safety. Advection fog, in contrast, occurs over a flat terrain when warm, moist air moves horizontally over a cooler surface, causing it to cool and condense. Radiation fog typically forms overnight when the ground cools rapidly, and steam fog arises when cold air moves over warm water, creating a visible steam-like effect. Each of these types of fog has distinct formation conditions and implications for aviation.