Clouds have been a fascinating subject for me, and always a challange to emulate.

Test 1:
This test was done a long time ago. It is very incomplete, and I didn't put much work into it. However, the concept of the stealth aircraft passing through the clouds would be incorperated in newer iterations.

Test 2:
This took a lot more work and rendering time. In fact, this animaton took over 100 hours to render at 640x480. Animation is still incomplete, as you can see. The volumetrics are coming along nicely, though.