Rain by Hassam
It is raining like crazy and as I am looking out the window the thought occurred how would one paint rain? That send me searching and I found samples of how other artists have treated the subject.
by Homer Winslow
Just about all of them have shown puddles of water. Most refrain from actually showing rain falling out of the sky for the exception of Homer Winslow, who added a few slanted slashes in the darkest parts of the barrels on the left. These are only seen once you look close and long enough. Most often props, like umbrellas or rain boots further give the impression that it might be raining.
Rain Break at Herman's was painted by Fairfax Artist Herb Beard
Note how the artist has blurred the background and made everything reflective in the foreground.
When wind and rain combine, everything moves in one direction. So if you are doing a landscape paintings with trees or have objects such as signs for example you can indicate the direction of the rain by making everything that might move with wind move in the same direction.
Remember that you do not show the actual rain, but give hints at what is happening relying on the viewer's brain to make the connection between the visual clues to conclude that it must be raining.