What is the primary characteristic of cumulonimbus clouds?

Cumulonimbus clouds are primarily characterized by their thick and towering structure. These clouds are associated with severe weather phenomena, including thunderstorms, heavy rainfall, and sometimes severe conditions such as hail, tornadoes, and lightning. The vertical development of cumulonimbus clouds can span several kilometers, making them one of the most vertically extensive types of clouds in the atmosphere. The towering nature comes from the strong updrafts that occur within them, allowing the clouds to develop not only in height but also in mass.

In contrast, low-altitude clouds tend to remain closer to the ground and do not have the pronounced vertical structure seen in cumulonimbus clouds. Thin and wispy clouds are typically associated with cirrus clouds, which are high-altitude clouds comprised of ice crystals and do not exhibit the characteristics of severe weather. Uniformly gray clouds are more indicative of stratiform clouds; however, cumulonimbus clouds can exhibit various colors depending on their thickness and the amount of sunlight passing through them. This distinctive thick, towering stature is what sets cumulonimbus clouds apart, making them easily recognizable during weather observations.