[Developer question] How does one animate weather overlays?

[skullywag]

Hi Devs,

Simply put I have tried adding my own weater def to the game calling a copy of the fog overlay class, this results in a tiled image moving across the screen but does not have the "rolling" effect that fog has on it ingame, did you guys do something special with the image itself that a simple PNG cannot do or am I missing something here?

Animation master material files? using the unity Material class?