What does the "C" represent in relation to cloud height in METAR?

The "C" in METAR does not specifically refer to cumulus or cumulonimbus clouds, which might lead to some confusion. Instead, in the context of cloud height, it refers to the ceiling, or more explicitly, the "cloud ceiling." The cloud ceiling is the height of the lowest layer of clouds that covers more than half of the sky, and it is crucial for aviation operations as it indicates the altitude at which visibility might be constrained.

Cumulonimbus clouds, while significant in weather reporting due to their association with thunderstorms and severe weather, are just a type of cloud. They do not represent a standardized height measurement in the METAR format. The distinction between various cloud types such as cumulus or cirrus is valuable in meteorology, but for decoding METAR reports, the term "C" is used instead to indicate the cloud ceiling. This specific metric directly impacts flight operations, safety, and planning, which is why understanding its meaning is critical.