Upslope fog forms when moist air is lifted as it travels up a slope, such as a mountain range. As the air rises, it cools due to the decrease in atmospheric pressure with altitude. When the temperature of the rising air drops to its dew point, water vapor condenses into tiny water droplets, creating fog. This process is closely linked to the principles of adiabatic cooling, where rising air cools as it expands.
In contrast, evaporation fog occurs when water vapor is added to the air as it evaporates from a body of water, leading to condensation near the surface. Radiation fog forms on clear nights when the ground loses heat quickly, cooling the air directly above it to below the dew point. Advection fog develops when warm, moist air moves horizontally over a cooler surface, cooling the air enough to reach saturation. While each of these fog types involves condensation, upslope fog specifically highlights the process related to air being lifted and cooled over a slope.