The document describes four main types of clouds: Cumulus clouds appear as large cotton balls and usually mean nice weather with a chance of light showers. Cumulonimbus clouds are large and dark like thunderclouds and can bring thunderstorms or even tornadoes. Stratus clouds look like a blanket covering the sky and often bring drizzle or light snow. Cirrus clouds are thin and wispy bands or patches that usually mean fair weather.