I have used both Nimble and SilverLining, and unfortunately- both are poor for flightsim usage.
There are many whitepapers available on the implementation and coding of clouds based on the simulation of light scattering, seen implemented in Wings of Prey, Ace Combat 5, HAWX, Rise of Flight, etc etc..
Here is the most recent example I can remember seeing, but there are many many third party and proprietary examples of this stuff..