1. Choose a photo you want to add rain to.
2. New layer. Edit> Fill> 50% Gray.
3. Filter> Noise> Add Noise. Select Gaussian / Monochromatic / 400%.
4. Filter> Blur> Gaussian Blur. (0.5%)
5. Image> Adjustments> Levels. Adjust the slider to reduce the noise.
6. Filter> Blur> Motion Blur. Adjust the angle that you want your rain to fall. Use a low distance of around 15 pixels.
7. In the Layers palette, change the drop-down box from 'Normal' to 'Screen'.
8. This is your first layer of rain. It will be your background layer of rain so use the Erase tool to erase the rain from the foreground.
9. Repeat steps 2 through 7 to create two new layers of rain. For the midground layer of rain, when you use the Levels tool, adjust the sliders so there is a little less rain than the backgorund rain layer. In the Motion Blur tool, increase the distance to a higher pixel. For the foreground rain, create even less rain, and increase the distance more to make the drops longer so they appear close up.
10. Here I just lowered the contast, saturation, and brightness of the background photo. I also lowered the opacity of the rain layers to make it look more realistic.
11. In a new layer above the background photo layer- Filter> Render> Clouds.
12. I used the Erase tool to erase the clouds in the foreground and then lowered the opacity.
13. Before and after.
