Icing and turbulence by cloud genus
Cumulonimbus (Cb) not in table.
| Genus | Turbulence | Icing | Icing condition |
|---|---|---|---|
| Cirrus (Ci) | none significant | none significant | - |
| Cirrocumulus (Cc) | some | some | supercooled droplets mixed with the ice crystals |
| Cirrostratus (Cs) | none | little if any | - |
| Altocumulus (Ac) | some | small amounts | - |
| Altostratus (As) | little or none | light to moderate | in the supercooled water |
| Nimbostratus (Ns) | very little | can be serious | near or below freezing |
| Cumulus (Cu, little vertical development) | some | none significant | - |
| Towering cumulus (TCU) | very strong | some clear icing | above the freezing level |
| Stratocumulus (Sc) | some | possible | at subfreezing temps, worst in the cloud tops |
| Stratus (St) | little or none | hazardous | near or below freezing |
Notes by genus:
- TCU: first stage of a thunderstorm. Worst entry short of Cb.
- Stratocumulus: ceiling and visibility usually beat plain stratus.
- Stratus: with fog or precipitation, troublesome for visual flying.
Low clouds (stratus, stratocumulus, nimbostratus, fog):
- Can carry supercooled droplets, hazardous icing.
- Low ceilings, hampered visibility, rapid change.
- Together can make VFR impossible.
Icing and turbulence differ:
| Genus | Turbulence | Icing |
|---|---|---|
| Altostratus | light | light to moderate |
| Nimbostratus | very light | can be serious |
| TCU | very strong | some clear icing above the freezing level |
Trap: calm-looking nimbostratus can carry serious icing.
References
- FAA Aviation Weather Handbook (FAA-H-8083-28) Appendix A
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25) ch.12