So, ich lasse nicht locker und bleibe beim Thema Wolken in P3D 2.3.
Anscheinend hat LM den BUG 
wirklich gefunden und bietet bald einen Hotfix an:
http://www.prepar3d.com/forum-5/?mingleforumaction=viewtopic&t=7984
Hello all. We found the issue that is likely causing the majority of cloud related issues in 2.3. Some of the cloud math got tweaked during 2.3 development and the size of clouds got doubled. We do plan on releasing a hot fix but will first prioritize known issues to see what fixes we can get in reasonably soon. In the meantime, you can resolve the cloud issue by doing the following:
Brows to the ShadersHLSL folder. This is in the main application folder where the Prepar3D.exe is. You may need elevated permissions to do this if you installed into program files with standard windows security settings.
Open Cloud.fx in notepad or another text editor
Look for this this line (should be around line 300 if you have line numbers enabled in your editor):
GetScreenQuadPositions( quad, width, height ); Scale the width and height down by half with this change:
GetScreenQuadPositions( quad, width*0.5, height*0.5 ); Save your changes and close the file
Our system should detect the newer file and rebuild the shader, but if it does not, you can clear the shader cache:
Not go to DRIVE:\Users\USERNAME\AppData\Local\Lockheed Martin\Prepar3D v2\
Delete the Shaders folder. This will clear the cache.
As I have posted in a few other threads, you can also disable the volume effect by finding this line:
#define VOLUMIZEand commenting it out
//#define VOLUMIZE The volume effect should be a 5-10% hit in the worst case, but the hit was being magnified because there were 4x as many pixels in the bigger cloud sprites. If you like the effect but turned it off for performance reasons, you may want to try turning it back on after fixing the cloud scale.
Beau Hollis
Rendering System Lead - Prepar3D® Team
