Creating rain in Photoshop

Here's a quick trick to create the illusion of rain in a photograph.
Here is the photo that I want to make it look like it's raining.

After about a minute of adding a couple layers and filters I got the following results.

Here are the steps I followed:
I duplicated my original layer. Out of habit, I always do this to protect the original image.

Next, I created a new layer by holding down the alt/opt key and clicking on new layer.
This method opens up the options I want for my new layer.
I changed the blending mode to hard light and selected the "Hard light neutral color" box.

 

Next I added noise to this gray fill. Filter - Noise - Add Noise. Make sure to select Gaussian and the Monochromatic button. Adjust the noise to your liking. 

To make the noise look like rain I went to Filter - Blur - Motion Blur. You'll want to add enough motion to add streaks but not long straight lines.

Because it appeared that the rain clouds were in the upper left, I adjusted the direction of the motion blur to come from the upper left.

The last thing I did was to add a layer mask to this top layer. I wanted to break up the rain a bit.

Make sure the default foreground and background colors are black and white.

With the layer mask selected I went to filter > render > clouds

If you are familiar with masks, you know that black conceals and white reveals.

So this mask of black and white broke up the pattern just a bit to make the rain look a little more realistic and resulting in this finished photo.