If you want to animate this, *do not animate the cloud layer* (at least not for *direction*). You want to add a Transform shader and use Translate, feed your *density shader* output into the transform, output of Transform into your cloud density shader input. Then animate the Translate values, z, y, z, to get movement of your cloud. Animating the density shader values themselves, e.g. 4D noise, is also an option to consider for some effects.
- Oshyan