Nimbus clouds often mean that a thunder storm is brewing: there may soon be thunder and lightning. Get out of the swimming pool! Nimbus really just means a cloud that already has rain or snow falling out of it. Can you see the rain falling in the picture to the right?
So you often see the names of clouds combined: a cumulonimbus cloud is a cumulus cloud, a puffy thick cloud, with rain falling out of it, and a stratonimbus cloud is a stratus cloud, a gray blanket cloud, with rain falling out of it.
To find out more about the atmosphere, check out these books from Amazon.com or from your library:
Learn by Doing - Clouds
More about clouds
More about Thunderstorms
More about Weather
Science for Kids home page
History for Kids home page