1. Feel right as rain
例：You'll see that if you have a good night's sleep, you'll feel as right as rain.
2. When it rains, it pours.
Tim: Not only did he lose his job, his car was also stolen. Both his laptop and iPhone were in it.
Charlie: Oh no. When it rains, it pours.
3. Rain on someone's parade
例：I'm having such fun, so please don't rain on my parade.
4. Rain check
例：I'd love to go for dinner, but I can't tonight. Can I take a rain check and get back to you?
5. Come rain or shine: whatever happens.
例：Don't worry. I'll be there for you on Thursday, come rain or shine.
6. Save money for a rainy day
My father always told me to save money for a rainy day. I'm so glad I took his advice.