I saw a similar rain animation here and decided to level-up my fluid sims.
This was done with ocean modifiers on 3 cubes and caustics from light sources. Plus my favorite transparent-plain-of-rain for drizzle effect.
Here is an upgraded version, (I think) the mist actually brightenned the scene because I used ‘screen’ as the blend mode between a full render with mist (which had pixelated mist which was too dense) over the original version. 
