FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesEasy
A pilot is planning a flight along a coastal route where warm, moist air is moving over a cold ocean current. Which type of fog is most likely to form under these conditions?
- ARadiation fog
- BSteam fog
- CAdvection fog
- DUpslope fog
Show answer & explanationAnswer & explanation
Correct answer: C. Advection fog
Advection fog forms when warm, moist air moves horizontally over a colder surface, such as a cold ocean current, cooling the air to its dew point. This is common along coastlines and can persist with wind, unlike radiation fog which requires calm, clear conditions over land.
Why the other options are wrong
- A. Radiation fog forms over land on clear, calm nights due to surface cooling, not from air moving over water.
- B. Steam fog forms when cold air moves over relatively warmer water, the opposite temperature relationship described here.
- D. Upslope fog forms when moist air is forced to rise along rising terrain, not over flat coastal water.
Advection Fog
Fog that forms when warm, moist air moves horizontally over a colder surface, cooling to saturation.
- Common along coastlines with warm air over cold currents
- Can occur with wind, unlike radiation fog
- Often extensive and persistent, difficult to forecast dissipation time
Memory trick: Advection = Air moves; Radiation = Radiates heat away at night.