Adding rain and clouds

[mdh21]

I have a landscape picture with a tree in the middle. I want the area left of the tree to stay how it is, but make the right side have rain and clouds. I have an idea on how to make the rain, but how do I select the right side so that the filters and adjustments I use are only applied to that side? I'm using Photoshop CS4.

[windrider86]

You can google Mura Meister plugins. Its a neat source for clouds
To only apply to one side of the image is fairly simple. One of two ways that i can think of.
Use the selection tool to select only the areas you want to apply the filter with or just apply the filter to the entire image and then mask off the areas you dont want it