It is not supposed to rain on a Sun Dance. But sometimes it does because something has gone wrong. The last Sun Dance at Porcupine is a good example. It rained on the second day because someone present was impure. Either a pledger or someone in the audience was not cleansed properly, so the thunder spirits brought rain down to help cleanse us. There was even thunder and lightning, but they didn’t harm anything. The lightning did not strike the sun pole, and we all remained happy because we understood what the problem was. We finished the dance and went home happy and pleased as we usually are when a Sun Dance is over.

Fools Crow, p. 138