FAA Sport Pilot Airplane (SPA)WeatherMedium
On a clear, calm night with high relative humidity, ground temperatures drop rapidly after sunset due to radiational cooling. Which type of fog is most likely to form under these conditions?
- ARadiation fog
- BUpslope fog
- CSteam fog
- DAdvection fog
Show answer & explanationAnswer & explanation
Correct answer: A. Radiation fog
Radiation fog forms over land on clear, calm nights when the ground cools rapidly through radiational heat loss, cooling the adjacent air to its dew point. It typically dissipates after sunrise as the ground warms.
Why the other options are wrong
- B. Upslope fog forms when moist air is forced up rising terrain and cools adiabatically.
- C. Steam fog forms when cold air moves over much warmer water, causing evaporation and condensation.
- D. Advection fog forms when warm, moist air moves horizontally over a colder surface, not from radiational cooling.
Radiation Fog
Fog that forms over land on clear, calm nights when the ground radiates heat rapidly, cooling nearby air to its dew point; it typically burns off after sunrise.
- Requires clear skies, light wind, and high humidity
- Forms shortly after sunset and thickens near sunrise
- Usually shallow and dissipates as the sun warms the ground
Memory trick: 'Radiation fog: the ground shivers itself into a blanket'