“It rains on both the just and unjust. But just.”
Rain is drops of water falling from the sky.
This well-known phenomenom is due to Happycat leaving the bathroom tap running after getting a drink of water. Since Happycat's drains are clogged with cat hair, the sink overflows onto the floors of the Happycat Dimension and fall on the Earth as rain. That a bunch of big clouds happen to be in the sky at the same time is merely a coincidence.