Need advice on how to create atmosphere and clouds like this.

[axel.g]

Hello, i'm trying Terragen right now, so i'm kinda new to this programm. I want to recreate atmosphere like this: please see attachment.

So kinda overcast dark sky, and heavy dark clouds with some breaks in them. The sun itself is not very apparent.

Right now i'm trying to understand how to make my sky dark like this. The atmosphere setting are quite interesting, seems like they trying to simulate real world sky. But it makes it kinda hard for me to understand how to achieve desirable effect 

Any advice appreciated.

[archonforest]

Indeed. Terragen is capable to create highly realistic atmo and clouds

The attached file can give you a starting point. Hope it helps.