Raining

This is an old photoshop technique, probably already here for 20 years.

1. Create a noise clip.
2. In DVE, scale it Y axis. 3. In color, adjust gain, gamma, contrast.

4. Blur it, more blur on y than x

5. Done, screen it over you background footages. Do a few layers with different size & blur, sandwich it between your foreground objects.

Autodesk SmokeTips & Tricks
http://mysmoke.blogspot.com