I definitely think there's a fair amount of atmospheric fogging and variation, like mist and fog. Seems that way. I think (hope) if they do add in some basic cloud it would be a late reveal along with any new ships/srvs.When the Viper flies overhead the parked commander walking on the ice world, it throws a shadow through what looks like some ground-hugging volumetric clouds.
I don't believe the flat fumerole smoke behaves like that?
Also, look at the refracting haze in the crater on the rocky world. Very different to the outgassing ground fog we see currently. I think we will be getting some basic clouds and volumetric effects, just not big dramatic clouds in the sky with weather fronts and stuff.