FAA Instrument Flight Instructor (FII)WeatherMedium
A pilot planning a coastal flight is briefed that warm, moist air is expected to move over the cold coastal waters overnight. What type of fog should the pilot expect to encounter?
- ASteam fog
- BRadiation fog
- CUpslope fog
- DAdvection fog
Show answer & explanationAnswer & explanation
Correct answer: D. Advection fog
Advection fog forms when warm, moist air moves horizontally over a colder surface, cooling the air to its dew point; this is common along coastlines where warm air moves over cold ocean currents. Radiation fog forms from nighttime surface cooling under clear, calm conditions, not from air mass movement.
Why the other options are wrong
- A. Steam fog forms when cold air moves over warmer water, the opposite scenario described.
- B. Radiation fog results from surface cooling at night, not horizontal air movement over cold water.
- C. Upslope fog forms when moist air is forced to rise along terrain, not over water.
Advection Fog
Advection fog forms when warm, moist air moves horizontally over a colder surface, cooling the air below its dew point.
- Common along coastlines with cold ocean currents
- Can occur day or night, unlike radiation fog
- Persists with wind, unlike radiation fog which dissipates with wind
Memory trick: Advection fog 'Advances' with wind over cold water.