What is Advection fog?

• A. It forms when warm moist air moves upward over mountains.
• B. It forms when warm, moist air moves horizontally over a colder surface.
• C. It forms when moist air rises over a warm surface.
• D. It forms only over dry land.

Answer: (B)

Advection fog forms when warm, moist air moves horizontally over a surface that is cooler than the air. As this air glides over the cooler surface, it loses heat to contact with the surface, the air temperature drops to the dew point, and water vapor condenses into fog. This type is common along coastlines or over ocean surfaces where warm, moist air from the water moves over cooler land or sea. It’s different from fog that forms from air rising or convection—uplift over mountains creates a different fog type, and fog over a warm surface from rising air isn’t advection fog. Also, advection fog isn’t limited to dry land; it can form over water too, whenever warm, moist air travels over a cooler surface.