What type of clouds are most likely to cause turbulence?

Cumulonimbus clouds are indeed the type most likely to cause turbulence. These clouds are characterized by their towering vertical structure and are associated with severe weather phenomena such as thunderstorms. Inside and around cumulonimbus clouds, there are strong updrafts and downdrafts that create significant air movement, leading to turbulence. The intense convective activity within these clouds results in variations in wind speeds and directions, which can affect aircraft flying nearby, making the experience of turbulence more pronounced.

In contrast, stratus clouds tend to form in stable air conditions and produce less turbulence, often resulting in overcast skies with light precipitation. Cirrus clouds, while high and wispy, are typically thin and do not generate turbulence. Altostratus clouds are also relatively stable and are associated with a gradual increase in cloudiness without the same intensity of vertical motion that causes significant turbulence. Thus, cumulonimbus clouds are the most notorious for turbulent conditions due to their robust and dynamic characteristics.