FAA Private Pilot Helicopter (PRH)WeatherEasy
A helicopter pilot operating along a coastal route notices fog forming as warm, moist air moves horizontally over a cooler ocean surface and then drifts inland. What type of fog is this?
- ARadiation fog
- BAdvection fog
- CUpslope fog
- DSteam fog
Show answer & explanationAnswer & explanation
Correct answer: B. Advection fog
Advection fog forms when warm, moist air moves horizontally over a colder surface, cooling the air to its dew point. It is common along coastlines and can persist with wind, unlike radiation fog which requires calm, clear conditions.
Why the other options are wrong
- A. Radiation fog forms from nighttime surface cooling under calm, clear skies, not horizontal air movement.
- C. Upslope fog forms when moist air is forced to rise along terrain, not over water.
- D. Steam fog forms when cold air moves over warmer water, the opposite temperature relationship.
Advection Fog
Fog produced when warm, moist air moves horizontally over a colder surface, cooling to saturation. Common along coasts and in winter over snow-covered ground.
- Requires wind to advect air over cold surface
- Can persist or thicken with increased wind (unlike radiation fog)
- Common in coastal and marine environments
Memory trick: Advection = air on the move over cold ground/water