Modeled in Lightwave.
Fluids imported from RealFlow.
Clouds simulated in TFD, converted to VDB and imported to Maxwell as a VDB in the Maxwell Volumetrics extension.
Rendered in Maxwell.
@ Forester: Thank you. I like these better than my architectural renderings just because they use geometry that is much more interesting. I think that my texturing skills would not do the geometry justice, so the best I could do was to light them in Maxwell.