Cumulonimbus (CB)

[Ref Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 12-16]

Cumulonimbus (CB) is a type of cloud with extensive vertical development and is perhaps the most dangerous cloud type – indeed, CB is a type of clouds of operational significance (對飛行有重要影響的雲)

CB appears individually or in groups and is known as either an air mass or orographic thunderstorm:

  • Air mass thunderstorms are caused by heating of the air near the Earth’s surface
  • Orographic thunderstorms are caused by the upslope motion of air in the mountainous regions


When CBs form in a continuous line (as a nonfrontal bands), we call that “squall lines”. It may associate with fast-moving cold front.


CBs or sort of extensive vertical clouds can be obscured by other cloud formations and are not always visible from the ground or while in flight, we call that “Embedded thunderstorms”, which are likely found in warm from occlusion.


If an aircraft enters a CB, the aircraft could experience updrafts and downdrafts that exceed 3000 fpm. In addition, CB can produce large hailstones, damaging lightning, tornadoes, and large quantities of water.

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