What does the abbreviation "CB" signify in a TAF?

The abbreviation "CB" in a TAF specifically stands for "Cumulonimbus clouds," which are large, towering clouds often associated with thunderstorms. These clouds are characterized by their vertical development and are crucial in aviation forecasts because they indicate areas of severe weather, including turbulence, heavy precipitation, and potential lightning activity. The presence of CBs in a TAF warns pilots and flight planners of the likelihood of adverse weather conditions that can impact flight safety.

In contrast to the other options, "CB" does not refer to cumulus clouds forming, clear skies, or cirrus clouds. Cumulus clouds are typically smaller and indicate fair weather rather than severe conditions. Clear skies indicate an absence of clouds, which is the opposite of what CB implies regarding turbulent weather. Cirrus clouds, while they can indicate high altitudes, do not have the same severe weather associations that Cumulonimbus clouds do. Thus, understanding that "CB" represents potential hazardous weather is essential for safe aviation operations.