Watersong is a celebration of onomatopoeia. Rain is a narrative about Sam and his grandfather's adventure in the rain. If you are teaching preschool combine these with Who Likes Rain? by Herbert Yee. If you have older students revisit Bill Martin Jr and John Archambault's beautiful word images in their poem Listen to the Rain.
The children I teach often ask where do the animals go when it rains, so books such as Gerda Muller's Where Do They Go in the Rain? and Harriet Ziefert's Where Does Kitty Go in the Rain? help address this question.
Just when the students start to whinge about not being able to go outside it is time to share Rain School by James Rumford and if you can find a copy, Children of the Yangtze River by Otto S. Svend because they will then appreciate their own school and ability to stay dry. These two stories show children as capable problem solvers, hard workers and useful in a time of difficulty.