Final Render

Here we have the final render, overall I'm rather satisfied with the look I managed to achieve. The rain itself and the atmosphere manage to capture the look I was after. However the fog effects could be better, although this is in part due to having to find a solution that wouldn't take too long to render aswell.

In taking this effect further I would like to refine the actual rain and perhaps use some more scripting to add in a bit of random behaviour for the particles (to simulate the wind changing perhaps). Also I would like to improve the fog, aswell as add a lightning bolt or some kind of dramatic moment.

Final Render Still

Using the volume fog technique I have created clouds in the sky to help create a sense of depth aswell as adding some more visual interest. I have also tweaked the lighting in order to more accurately reflect the darker IBL and to get a moodier and more realistic result. The final render is currently in progress and shall be uploaded shortly, once it is complete.

(Pretty Much) Final Effect Still

So, this is a still from what the final render will look like, beyond tweaking. The fog itself will be animated and If I have time Id like to darken the sky a bit (with another volume primitive probably), and perhaps add a flash of lightning.

Volume Primitive Fog.

Well, after running through a few different ideas to make the fog. Including using sprites, as well as textures rendered on geometry planes. I settled on adding back in the very simple atmospheric fog to kind of "wash" the scene. As-well as making use of the volume primitives again. This combined with a 3d texture makes for an acceptable fog effect, taking a cue from the Maya fluid effect, I am going to use an expression to control the timeslider that will animate the fog. This solution has provided both a reasonable aesthetic outcome aswell as a reasonable render time.

Maya Fluids Fog

I tried to use the Maya fluid system to create a fog for the clouds, after a failed attempt trying to use sprites. However this method of creating the fog increases the render times to an unacceptable amount. However I an aware of another technique used by Alex Alvarez in several of his images (Including "Dirge" which was the basis for this project initially).
However here he explains his use for creating some background fog in his image "Gathering"
I hope to utilize the same technique as well as some expressions to get an animated fog that renders quickly.

Lighting Tweaks

Here we have the rain, with its size and lighting tweaked to closer match the reference, as-well as what the the rain would look like on a plain background, which could be used later for compositing. I want to try and find a better solution for the fog as-well, one that can be animated, however fog in the past is what has made the render times impractical, so hopefully I will find a good solution.

Reference and Render Test 02

Here we have some more reference footage and images.As you can see it was raining incredibly heavily when I took these. There is some things that I noticed aswell, Im sure its more to do with the camera I was using but the streaks in these images are a lot shorter than the ones In my current renders.
Secondly, the rain is illuminated a lot brighter than I currently have it, and so in order to match the real rain better, I will need to tweak the render settings and the lighting.
Currently I amen't using any motion blur as it increases render times to an unacceptable degree, I'm using different anti-aliasing filters to blur the result of the image to get a better look for now though.

Render Test 01

The first test render of the rain effect, I'm reasonably happy with how its falling at this stage, though it could benefit from falling faster. However looking at my reference, the lighting is off and I feel that the environment fog is too dark as-well and so the effect is not as visible as I would like.