Which type of cloud formation indicates severe turbulence?

Cumulonimbus clouds are associated with severe turbulence due to their intense vertical development and the atmospheric conditions in which they form. These clouds are often linked to thunderstorms and can produce significant updrafts and downdrafts, resulting in highly unstable air. The vertical extent of cumulonimbus clouds can reach great heights, allowing for the creation of various types of turbulence, including clear air turbulence and turbulence associated with precipitation and wind shear.

Stratus clouds typically result in stable atmospheric conditions and are formed in layers; they do not exhibit the turbulent characteristics of cumulonimbus clouds. Nimbostratus clouds, while often resulting in steady rain, are also linked to stable conditions and do not typically indicate severe turbulence. Altostratus clouds are generally found at mid-level altitudes and are associated with broader weather patterns rather than localized severe turbulence. In contrast, cumulonimbus clouds represent a clear signal of potential severe turbulence, making them the correct answer.