FAA Private Pilot Airplane (PAR)Weather Theory and ServicesHard
A pilot's weather briefing reveals a temperature profile with a surface temperature of -3°C, but a layer of warmer air aloft above 4,000 feet reporting temperatures around +5°C. Rain is falling from that warm layer into the sub-freezing air near the surface. What icing hazard does this scenario describe?
- ARime ice forming within stratiform clouds at high altitude
- BClear ice forming inside actively growing convective cells
- CFrost accumulation due to radiational cooling overnight
- DFreezing rain caused by warm air aloft overrunning colder air at the surface
Show answer & explanationAnswer & explanation
Correct answer: D. Freezing rain caused by warm air aloft overrunning colder air at the surface
This classic freezing rain setup occurs when warm air overruns a shallow layer of subfreezing air near the surface, often associated with a warm front. Precipitation falls as liquid rain through the warm layer, then becomes supercooled and freezes on contact with the cold surface or aircraft below.
Why the other options are wrong
- A. Rime ice typically forms in stratiform clouds with small supercooled droplets, not from a warm-over-cold temperature inversion producing rain.
- B. Clear ice in convective cells results from large supercooled droplets in cumuliform clouds, not this layered temperature structure.
- C. Frost forms from radiational cooling on clear nights, unrelated to precipitation falling through a temperature inversion.
Freezing Rain Formation
Freezing rain forms when precipitation falls as liquid through a warm layer aloft, then becomes supercooled while passing through a shallow subfreezing layer near the surface, freezing on contact with cold surfaces.
- Commonly associated with warm fronts overrunning cold air
- Requires a temperature inversion with warm air above freezing, cold air below
- Considered one of the most hazardous icing conditions for aircraft
Memory trick: Warm rain falls, cold ground waits — instant ice on contact