Wolfgang Mieder, A Dictionary of American Proverbs (1992) suggests three (seemingly related) sayings that use rain as a metaphor. The most familiar of these (noted by Greybeard in a comment beneath the posted question) is
Rain falls alike on the just and the unjust.
The sense here is that when large-scale trouble occurs, there is no discrimination between victims on the basis of their personal virtue or vice.
A similar sentiment is expressed in this alternative saying:
All who travel in the rain get wet.
...except that here the question of personal merit doesn't come up at all.
A slightly different take on the underlying idea appears in this saying:
The rain that rains on everybody else can't keep you dry.
That is, the particular misfortunes that others suffer in a general calamity don't immunize you from injury or even (in any practical sense) reduce your own exposure to harm.