FAA Part 107 Remote Pilot (UAG)WeatherEasy
A remote pilot plans a pre-dawn flight over a rural field. The night was clear with light winds and high relative humidity, and the ground has cooled rapidly overnight due to radiational heat loss. Which type of fog is most likely to have formed under these conditions?
- AUpslope fog
- BSteam fog
- CRadiation fog
- DAdvection fog
Show answer & explanationAnswer & explanation
Correct answer: C. Radiation fog
Radiation fog forms over land on clear, calm nights when the ground radiates heat rapidly and cools the air just above the surface below its dew point. Advection fog requires warm moist air moving over a colder surface, steam fog forms when cold air moves over warm water, and upslope fog forms when moist stable air is forced up rising terrain.
Why the other options are wrong
- A. Upslope fog needs moist stable air being lifted mechanically by terrain, not a flat rural field.
- B. Steam fog forms when cold, dry air moves over relatively warm water, causing evaporation and condensation.
- D. Requires horizontal movement of warm moist air over a cold surface, not calm clear-night radiational cooling.
Radiation Fog
Fog that forms over land on clear, calm nights when the ground cools rapidly, cooling the adjacent air below its dew point.
- Requires clear skies, light wind, and high humidity
- Forms in low-lying areas and valleys where cool air settles
- Usually dissipates within a few hours after sunrise as the ground warms
Memory trick: 'Radiation fog Rises at night when the ground Radiates its heat away.'