Cumulus clouds are puffy cotton-like clouds with flat bases around 100 miles above ground and rounded cloud tops. Cumulonimbus clouds are tall thunderstorm clouds with dark bases within 300 miles of the surface that release large amounts of energy and can cause tornadoes, thunder, and lightning. Cirrus clouds are thin, curly feather-like clouds that are the highest clouds, forming above 20,000 feet and often appear first in a blue sky. Stratus clouds are uniform gray clouds that can cover the whole sky in a fog-like form without reaching the ground, sometimes drizzling. Altocumulus clouds are puffy gray or blue-gray middle level clouds composed of ice crystals and water droplets that