I have been trying to manage the rain effect for such a long time so I have spent some time and made myself a brush set for convenience. There are four brushes, each one of a different type, so that you can determine the direction(Brush Tip Shape-Angle) in which the rain is falling and along with the Motion Blur filter to emphasize the motion effect.
The background has nothing to do with the brushes (nor it appears in the actual brush when used) I have just used it to show what the brushes look like. For even better results try them with a Pen Tablet
Thanks!
I used your stock here:
[link]
Thanks so much