A PIREP reports the following temperature profile during a descent: -6°C at 8,000 feet, +4°C at 5,000 feet, and -2°C at the surface. Precipitation is falling as rain that freezes immediately on contact with the aircraft and with ground structures. This temperature profile and precipitation type are classic indicators of
- AA dry microburst environment with no measurable precipitation
- BFreezing rain caused by a warm layer aloft above a subfreezing surface layer
- CRime icing forming in stratiform clouds at a constant subfreezing temperature
- DVirga that evaporates completely before reaching the surface
Show answer & explanationAnswer & explanation
Correct answer: B. Freezing rain caused by a warm layer aloft above a subfreezing surface layer
This is the classic freezing rain temperature profile: precipitation forms as snow aloft, falls into a warm layer (+4°C at 5,000 ft) where it melts into rain, then falls into a shallow subfreezing layer near the surface (-2°C) without refreezing into ice pellets, remaining as supercooled liquid that freezes instantly on contact — a serious icing hazard often involving supercooled large droplets (SLD).
Why the other options are wrong
- A. A dry microburst involves virga and strong outflow winds with little to no precipitation reaching the ground, not freezing rain.
- C. Rime icing occurs in small supercooled droplets within clouds at fairly constant subfreezing temperatures, not with a melt-refreeze profile.
- D. Virga would evaporate in dry air before reaching the ground, not freeze on contact as described.
Freezing Rain Formation
Freezing rain forms when snow falls into a warm layer aloft, melts into rain, then falls through a shallow subfreezing layer near the surface without refreezing, striking surfaces as supercooled liquid that freezes on contact.
- Requires warm layer aloft above a subfreezing surface layer
- Differs from ice pellets, which fully refreeze before reaching the surface
- Associated with supercooled large droplets (SLD), a severe icing hazard
Memory trick: Snow melts in a warm blanket aloft, then freezes the instant it hits the cold ground — freezing rain.