FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesEasy
A commercial pilot is briefed that warm, moist air is moving horizontally over a colder land or water surface, cooling the air to its dew point near the surface. Which type of fog is most likely to form under these conditions?
- ASteam fog
- BAdvection fog
- CUpslope fog
- DRadiation fog
Show answer & explanationAnswer & explanation
Correct answer: B. Advection fog
Advection fog forms when warm, moist air moves horizontally over a colder surface, causing the air to cool to its dew point. It is common along coastlines and can persist with wind, unlike radiation fog.
Why the other options are wrong
- A. Steam fog forms when cold air moves over warmer water, the opposite temperature relationship.
- C. Upslope fog forms when moist air is forced up rising terrain and cools adiabatically.
- D. Radiation fog forms from nighttime cooling of the ground under calm, clear conditions, not horizontal air movement.
Advection Fog
Fog formed when warm, moist air moves horizontally over a colder surface, cooling to saturation.
- Common along coastlines and over cold ocean currents
- Can occur with wind (unlike radiation fog)
- Often widespread and persistent
Memory trick: Advection = 'A' for Air-moving-Across cold ground.