Thanks, Bob.
Changing the weather from plain and static to 3D clouds with a Silver Lining allows you to gauge the impact it has on the performance of your system.
There are many new variables introduced, new .dll system extensions that interface with your video card's drivers, etc.
So far, the player's verdict is mixed, though the impact on performance is noted by almost everybody.
Inside the data\Silverlining you'll find the assets used, a few .tga files that seem to contain alfa channel masks of cirrus clouds, which indeed are whispy and mostly see-through, and some nice moon faces/phases.
I don't know if all cloud shapes are being used, and wether cumulus clouds actually bulge and grow in the sky above our scenarios.
There is a special directory of cumulonimbus clouds, the thunderstorm with the anvil on top, reaching up to the stratosphere.
I did find some lightning on first glance over the files. but no thunder or other audio. There are some feeble thunderstorm effects in a Sherman Hill scenario.
There seems to be no night sky definition with a public domain star atlas being used. (Run8 has a beautiful night sky in the desert, with the constellations etc. quite recognisable)
There is an annotated general config file, and a cloudatlas.tga graphic.
The effects seem to rely on the actual DX version used, which in the case of Railworks is DX9, right?/
Lots of stuff to play with, but wether realistic ground fog or those low clouds in mountain valleys can be created I don't know.
Here is the website of the proprietor of the Silver Lining system:
http://www.sundog-soft.com/sds