What is advection fog?

Advection fog forms when warm, moist air moves over a cooler surface, which can often be cold water. This temperature difference causes the moisture in the warm air to condense into tiny water droplets, resulting in fog. The process relies on the movement of air masses, hence the term "advection," which refers to the horizontal transport of air.

This type of fog is commonly seen near coastal areas where warm air from the land moves over the cooler ocean waters, leading to visibility issues for navigation and sailing. The other options do not accurately describe the mechanisms behind advection fog; for example, fog that forms overnight typically results from the cooling of the ground at night, not necessarily involving the movement of warm air over cold water. Similarly, fog created by high temperatures would be more associated with steaming from water rather than the advection process, and fog that develops in mountain regions may have different formation conditions more related to temperature inversion and moisture in the air specific to those altitudes.