1
general::
Phrase(s): rain or shine
no matter whether it rains or the sun shines. (See also come rain or shine.) • Don’t worry. I’ll be there rain or shine. • We’ll hold the picnic—rain or shine.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
No matter what the circumstances, as in We promised we would finish the project tomorrow, rain or shine. This term, first recorded in 1905, still refers to weather, as well as other uncertainty, and always implies that an activity will be carried out, no matter what. For a synonym, see HELL OR HIGH WATER.
American Heritage Idioms