What type of fog occurs when an air mass passes over an area of rapidly increasing elevation?

The correct answer is Upslope Fog. This type of fog occurs when moist air moves up terrain such as hills or mountains, where the elevation rapidly increases. As the air rises, it expands and cools adiabatically, which can lead to condensation of water vapor and the formation of fog. This process is particularly effective in moist conditions because the elevation causes a drop in temperature, reaching the dew point where the moisture in the air condenses into tiny water droplets that create fog.

In contrast, radiation fog typically forms under clear skies during the night when the ground cools rapidly, causing moisture near the ground to condense. Advection fog results from warm, moist air moving over a cooler surface and cooling to its dew point, whereas evaporation fog is produced when cold air meets warm, moist air (generally over a body of water). Each of these fog types has distinct conditions for formation, making Upslope Fog unique to areas of rising terrain.