Rain can mean so many different things.
Depending on the movie / show / book and its setting, rain could mean despair and hopelessness, a new beginning, and/or disaster.
What I mean is:
As popularised by British/Irish poets rain is used to convey the despairing feelings of the mourning family and friends of the deceased. (like tears running from an eye, among other things)
In many cultures where rain is a very rare and precious thing, rain can mean the absolute definition of living and the continuation of a way of life.
It can also be seen as the life-giver to the drought-ridden, or the end of salvation to those to whom a flood will bring the end of days.
Rain, as a technique in literature, can help to describe Spring, Summer, or Winter. (Not Autumn interestingly)