What are the effects of rain on pool chemistry?

I have read posts where people justify large FC loss due to rain overnight. Other than dilution, how will rain effect the FC levels?

I know that rain can make pH rise due to aeration, but will it have any other effect?

I know it should dilute Alk, CH and CYA, anything else to be aware of?

We received 5 inches of rain overnight and I have backwashed out about an inch. I think I will vacuum to waste tomorrow to drain it lower.