What occurs if moist warm air moves over cold surfaces?

When moist warm air moves over cold surfaces, it cools down as it loses heat to the colder surfaces below. This cooling can cause the air to reach its dew point temperature, which is the temperature at which water vapor condenses into liquid water. As a result, tiny water droplets form, leading to the development of fog known as advection fog.

Advection fog typically forms when warm, moist air mass flows over colder ground or water bodies, causing the air temperature to drop and humidity to rise to saturation point. The presence of this moisture in the air contributes to the visibility issues associated with fog, which can significantly impact transportation and other activities.

The other options do not accurately describe the phenomenon that occurs in this situation. Cumulus clouds, for example, are typically associated with rising air and convection processes. Stable air layers refer to situations where vertical motion is suppressed, which is not the case when warm air interacts with cold surfaces. Thunderstorms require more specific conditions for formation, including significant instability and lift, which aren't presented in this context. Thus, the formation of advection fog is the most appropriate outcome when moist warm air moves over cold surfaces.