rain

rain be as right as rain be perfectly fit and well.
come rain or shine whether it rains or not; whatever the weather.
rain before seven, fine before eleven traditional weather saying, mid 19th century.
rain cats and dogs rain very heavily; the phrase is first recorded in 1738, used by Jonathan Swift, but the variant rain dogs and polecats was used earlier in Richard Brome' The City Witt (1653). The origin is not known, although explanations adduced include a connection with the supernatural (cats were associated with witches, believed to be able to raise storms), as well as the suggestion that in earlier times heavy rain would have resulted in the bodies of drowned dogs and cats floating in the streets and gutters. Cats and dogs are also proverbial for the enmity between them.
rain on someone's parade in North American usage, prevent someone from enjoying an event; spoil someone's plans.
take a rain check said when politely refusing an offer, with the implication that one may take it up at a later date (a rain check is a ticket given for later use when a sporting fixture or other outdoor event is interrupted or postponed by rain).

See also blessed are the dead that the rain rains on, if in February there be no rain, rains, rainy, Saint Swithin's day, if thou be fair.