What atmospheric condition typically leads to the formation of advection fog?

Advection fog is specifically formed when moist air moves horizontally over a colder surface, such as water or land. As the warm, moist air travels over the cooler surface, it cools down and reaches its dew point. This causes the water vapor in the air to condense into tiny droplets, resulting in fog. This process is primarily a result of the movement of air rather than static conditions, which distinguishes it from different types of fog that can form under stagnant conditions or without any movement.

In contrast, warm, moist air settling over a cool surface under calm conditions refers more closely to radiation fog, which forms typically during the night when surface temperatures drop, and both the surface and the air close to it cool down together. Similarly, a land breeze blowing a cold air mass over a warm water current would be more likely associated with the formation of different types of fog or other weather phenomena that are not specifically categorized as advection fog. Finally, high humidity levels during nighttime cooling can lead to the development of fog as well, but it does not specifically denote the horizontal movement of air that characterizes advection fog. Thus, the correct choice highlights the essential condition of moist air moving over colder surfaces, which is the defining characteristic of advection fog formation