What type of clouds resemble fluffy cotton balls, indicate thermal uplift, and can produce severe turbulence?

Cumuliform clouds are characterized by their puffy, cotton-ball appearance, and they are typically associated with strong thermal uplift. This type of cloud formation occurs when warm, moist air rises and cools, leading to condensation and the development of these clouds. The vertical development of cumulus clouds can reach significant heights, and as they grow, they can contribute to atmospheric instability.

Cumuliform clouds are also known for their potential to produce severe turbulence, particularly in their mature stages. The turbulence arises from the strong updrafts and downdrafts commonly found within these clouds, making them crucial for pilots to monitor when flying, especially in stormy conditions.

In contrast, the other types of clouds listed have different characteristics; stratiform clouds are generally layered and indicate stable atmospheric conditions, while cirriform clouds are wispy and high-altitude, not associated with turbulence. Altostratus clouds, being thin gray or blue clouds covering the sky, typically indicate moisture but do not imply the violent updrafts seen in cumulus clouds. Thus, cumulus clouds are the correct answer due to their association with thermal uplift and potential for severe turbulence.