FAA Private Pilot Airplane (PAR)Weather Theory and ServicesMedium
A pilot flying along a coastline notices fog forming as warm, moist air is carried by wind over a much colder ocean current near the shore. This type of fog is best classified as:
- AUpslope fog
- BRadiation fog
- CSteam 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, such as cold ocean water, cooling the air to its dew point. Unlike radiation fog, which forms from nighttime surface cooling under calm, clear conditions, advection fog requires wind to transport the moist air over the cold surface and can persist with light-to-moderate winds.
Why the other options are wrong
- A. Upslope fog forms when moist air is forced to rise and cool along rising terrain, not over water.
- B. Radiation fog forms from surface cooling on clear, calm nights, not from air moving over cold water.
- C. Steam fog forms when cold air moves over much warmer water, the opposite temperature relationship.
Advection Fog
Advection fog forms when warm, moist air moves horizontally over a colder surface, cooling the air to saturation; it commonly occurs along coastlines and requires wind for formation.
- Requires horizontal wind movement, unlike radiation fog
- Common along coasts where warm air meets cold currents
- Can be widespread and persist longer than radiation fog
Memory trick: Advection = Air moving over cold water