FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesHard
During early morning hours, a pilot observes wisps of fog rising from a lake surface into much colder air above, resembling smoke. What condition produces this type of fog, and what hazard is most associated with it?
- ASteam fog caused by cold air moving over relatively warm water; hazard is potential for low-level turbulence and icing
- BRadiation fog caused by nighttime cooling; hazard is reduced visibility only near the surface
- CAdvection fog caused by warm moist air moving over cool water; hazard is widespread low ceilings
- DUpslope fog caused by moist air rising along terrain; hazard is icing above the freezing level
Show answer & explanationAnswer & explanation
Correct answer: A. Steam fog caused by cold air moving over relatively warm water; hazard is potential for low-level turbulence and icing
Steam fog (evaporation or 'sea smoke') forms when cold, dry air moves over relatively warm water, causing rapid evaporation that saturates and cools the air just above the surface, producing a smoke-like rising fog. It is often associated with low-level instability that can produce turbulence and icing hazards near the surface.
Why the other options are wrong
- B. Radiation fog forms from surface cooling over land under clear, calm skies, not by cold air over warm water.
- C. Advection fog involves warm air over cool surfaces, the opposite temperature relationship of steam fog.
- D. Upslope fog results from moist air rising along terrain, unrelated to temperature contrast over water.
Steam Fog (Sea Smoke)
Fog formed when cold air moves over relatively warm water, causing evaporation and saturation that produces a smoke-like rising fog.
- Also called evaporation fog or 'sea smoke'
- Forms when cold air overlays much warmer water
- Can create low-level instability, turbulence, and icing hazards
Memory trick: Steam fog: cold air, warm water, smoke on the lake.