How to say "on a rainy day" in English?

rain; Rain; The rainy season (in the tropics); Something that rained down.

v. it's raining; (Cause) to fall heavily, rain down.

rain, an English word, is a noun, a transitive verb and an intransitive verb. When used as a noun, it means "rain; Rain; Rainy days; Rainy season, name; (French) blue; (British) Rennes; (Luo, Jie) Ryan ",when used as a transitive verb, means" give a lot; Cause a lot of rain to fall ",when used as an intransitive verb, it means" rain; Rainfall. "

Example:

There will be rain in all parts tomorrow.

Tomorrow, there will be rain in all areas.