A dispatcher is comparing two icing reports. One flight in a shallow stratus deck reports freezing drizzle with no rain reported at any altitude, while another flight through the same region encountered freezing rain below a warm frontal surface. What atmospheric structure most likely explains the freezing drizzle report as distinct from the freezing rain encounter?
- AA deep warm layer aloft where snow melted completely before refreezing near the surface
- BA strong temperature inversion capping a deep convective cloud with active ice-crystal growth
- CA dry adiabatic layer extending from the surface to above the freezing level
- DA shallow, stable cloud layer of small supercooled droplets with no melting layer or ice-crystal process aloft
Show answer & explanationAnswer & explanation
Correct answer: D. A shallow, stable cloud layer of small supercooled droplets with no melting layer or ice-crystal process aloft
Freezing rain typically forms when snow falls into a warm layer aloft, melts into rain, and then refreezes on contact with a subfreezing surface layer. Freezing drizzle, by contrast, forms in shallow, stable stratus clouds composed entirely of small supercooled liquid droplets with no melting layer or significant ice-crystal process, so the droplets remain liquid and small until they contact a subfreezing surface.
Why the other options are wrong
- A. This describes the classic freezing rain formation process, not freezing drizzle.
- B. Deep convective clouds with ice-crystal growth are unrelated to freezing drizzle formation.
- C. A dry adiabatic layer would prevent cloud/precipitation formation altogether.
Freezing Drizzle vs Freezing Rain
Freezing rain forms when snow melts in a warm layer aloft and refreezes near the surface; freezing drizzle forms in shallow all-liquid stratus clouds with small supercooled droplets and no melting layer.
- Freezing rain: warm layer aloft melts snow into rain
- Freezing drizzle: shallow stratus, small supercooled droplets, no melting layer
- Both cause hazardous clear ice accretion on aircraft surfaces
Memory trick: Rain melts then refreezes; drizzle never melts, just stays cold and small.