I didn't animate the scale, but there are three localised clouds that are the "leaders" of the avalanche. I simply animated the position of them and stretched the cloud fractal by a factor of 2 into the direction they are heading to, but I didn't touch the warping.
The cloud fractals are animated by a transform shader down the y-axis and also a bit into the direction of the avalanche, but not very much.
There are also two bigger localised cloud with different density and noise settings additionally to the three mentioned ones, which are stretched differently.
It took quite a while and a lot of testing to get the motion and the speed of the clouds right.
I hope this makes sense, but I don't think so. That's why I decided to share the file in the file sharing section. Play around with it and have fun.
