The type of cloud typically associated with thunderstorms is the cumulonimbus cloud. These clouds are tall, towering, and can reach great heights in the atmosphere, often resembling an anvil shape at their tops. Cumulonimbus clouds are formed from rising warm, moist air that cools and condenses. They can produce severe weather phenomena including lightning, heavy rain, hail, and tornadoes. The presence of these clouds is an indicator of instability in the atmosphere, which leads to the development of thunderstorms and convective activity.