Which type of cloud is commonly a sign of an unstable atmosphere?

Cumuliform clouds are typically associated with an unstable atmosphere because they form as a result of rising air that cools and condenses. This process is driven by vertical uplift, which occurs in unstable conditions where warm, moist air at the surface rises quickly into cooler air above. As this air continues to rise, it can lead to the development of cumulus clouds and, in more severe cases, cumulonimbus clouds, which are capable of producing thunderstorms. The characteristics of these clouds, including their vertical development and often fluffy appearance, indicate strong convection and instability in the atmosphere.

Stratus clouds, on the other hand, usually form in stable conditions where there is little vertical movement of air. Nimbus clouds indicate the presence of precipitation but do not specifically convey information about atmospheric stability. Cumulonimbus clouds can also indicate instability but are a specific type of cumulus cloud known for severe weather. Understanding that cumulus clouds reflect the initial stages of uplift in unstable air helps clarify their role in meteorological phenomena associated with instability.