FAA Aircraft Dispatcher (ADX)MeteorologyMedium
A dispatcher is planning a flight into a coastal airport during the late morning. A weather observation shows warm, moist air flowing in from over the ocean directly onto a much cooler land surface, with visibility dropping rapidly to near zero. Which type of fog is most likely forming?
- AUpslope fog
- BAdvection fog
- CSteam fog
- DRadiation fog
Show answer & explanationAnswer & explanation
Correct answer: B. Advection fog
Advection fog forms when warm, moist air moves horizontally (advects) over a colder surface, cooling the air below its dew point. It is common along coastlines where warm ocean air moves over cooler land or water, and unlike radiation fog it can occur with wind and cloud cover.
Why the other options are wrong
- A. Upslope fog forms when moist air is forced to rise and cool along rising terrain, not from horizontal flow over a cold surface.
- C. Steam fog forms when cold air moves over much warmer water, causing evaporation, the opposite temperature relationship.
- D. Radiation fog requires clear skies and calm winds over land at night, not horizontal air movement over a cold surface.
Advection Fog
Fog that forms when warm, moist air moves horizontally over a colder surface, cooling to the dew point.
- Requires wind to advect the air mass (unlike radiation fog)
- Common along coastlines and over cold ocean currents
- Can be widespread and persist with wind, unlike radiation fog which dissipates with sun/wind
Memory trick: 'ADvection = Air Drifts' over cold ground to make fog.