I decided to tackle this problem by having different layers working together. Which layer to do first? Even in the highest places in Earth, it is likely to find a layer of clouds over your head. I did some experiments over the weekend on how this particular layer could be rendered.
Here are a couple of early screenshots for your consideration:
It is a very simple and fast method that allows clouds to animate and evolve over time. You can go from a clear sky to a very cloudy one as well. It takes into account the sun's position and does some basic scattering and self shadowing.
These clouds are rendered in the same skydome that performs the day-night cycle, so they do not add any new geometry. This is also the problem with this method: This is a flat layer. There is the impression of volume thanks to how the light is computed, and this trick holds as long as the clouds do not move too fast. If you make them sprint over your head it becomes obvious it is a flat layer. You cannot also come too close to these clouds, that also kills the illusion.
For what it does, I think the method is quite neat, especially if you don't have much GPU cycles to spend in clouds. It does not use any textures or any other resources. This is 100% GPU so it would run nicely in demos or WebGL frames. I think it deserves a future technical post on its own, that of course assuming you guys like how they look.
Let me know what you think by dropping a comment.