Examples of rain metaphors include "pouring rain," "rain washed light," "rain dancing across the meadow" and "rain soaked skin." A metaphor is a figure of speech using words in ways that are not literal. For example, rain doesn't literally pour from the sky, wash light, dance or soak through skin.
Rain is also used in similes such as "the rain is hitting the ground like thousands of horse hooves." The difference between a metaphor and a simile is that similes use "like" or "as" when creating their comparisons.
Rain is also used in idioms such as "it is raining cats and dogs."