Just a quick vfx dev post explaining this effect I made a few months ago:
I first rendered out a fluid simulation from maya onto photoshop (with separate color channels for variance), made my grey-packs in after effects, then set those up in blueprint and did the rest of the fine-tuning inside of cascade.
Definitely a steeper learning curve than just painting flipbooks by hand in photoshop but after you get the hang of it, it's definitely quicker and great for naturalistic effects.