Not only can sky textures produce moving cloud effects but most have properties for emitting light.
The angle that light shines in the vertical and horizontal axis and the emitted colour of light will vary between each sky texture.
Some sky textures also place a global fog effect in to your world.
The specific properties of each sky texture can be found in the skies.shader file in the RTCW/main/scripts folder.

If I have missed a *working* sky texture from this list or made any errors please email me at
kev.bolt@btinternet.com

For all images the angle of view is south.
Select image for larger picture.