Personally I am not a fan of this cloud. Clouds may be good for this image. But This one is over taking to much of the rest of the scene for me. Really I dont think you should worry too much about the clouds or "mood" yet. Deal with that stuff at the end once you have made your terrain. Then decide on you final comp, then decide on the mood and atmo.
There is still a lot of texturing and detailing to do on the ground. I think that is most important. Personally, if you get the terrain great, then I wont care if its a sunny day or a dreary day, Ill be happy to stand there in the rain even. Just my feeling.