What does the presence of "CB" imply in a METAR cloud report?

The presence of "CB" in a METAR cloud report indicates the existence of cumulonimbus clouds. Cumulonimbus clouds are commonly associated with thunderstorms and significant weather phenomena, such as heavy rain, lightning, and severe turbulence. These clouds are capable of developing vertically to great heights, forming an anvil shape at the top, and indicate a strong weather system.

Understanding this term is crucial for air traffic control and aviation safety, as it alerts pilots and controllers to potential severe weather conditions in the vicinity, allowing them to make informed decisions regarding flight paths and safety measures.