Which type of cloud is primarily associated with severe thunderstorms?

The correct answer is the type of cloud known as cumulonimbus. These clouds are highly indicative of severe thunderstorms due to their towering structure and extensive vertical development. Cumulonimbus clouds can rise to great heights in the atmosphere, reaching the troposphere's upper levels and often featuring an anvil shape at the top, which signifies intense convective activity.

Cumulonimbus clouds are capable of producing a variety of severe weather phenomena, including heavy rainfall, lightning, hail, and tornadoes. Their formation is largely driven by strong updrafts, which contribute to the development of the storm and its associated weather impacts.

The other cloud types listed do not typically exhibit the characteristics associated with severe thunderstorms. Stratus clouds are low, uniform clouds that usually bring light precipitation and are not associated with thunderstorms. Cirrus clouds are high, wispy clouds that indicate fair weather rather than stormy conditions. Nimbostratus clouds are thick, dark clouds that produce steady, light to moderate precipitation but lack the severe weather characteristics found in cumulonimbus formations.