Special cumulus clouds which bring thunderstorms are called cumulonimbus . Cumulonimbus clouds are dark because their bases are low, but their tops can reach high up into the atmosphere. Rain can form in any part of a cumulonimbus cloud. Rain which does not reach the ground is called virga . . Clouds that are flat and look like blankets in the sky are called stratus .
Rain can also fall from stratus clouds.
If rain is a steady drizzle which lasts for a while, it most likely comes from stratus clouds. Stratus Clouds look like a blanket Cirrus clouds are high up in the atmosphere. Thin, wispy clouds are called cirrus and are usually high up in the atmosphere. They are made of ice crystals since the higher air is colder. There is not enough moisture in cirrus clouds to cause rain.