Creating Realistic Clouds
Start by opening an image with a wide sky area.
Press Q to enable quick mask. From filter menu select render>>clouds.
From filter menu select render>>difference clouds. Press Ctrl+F, 5 times to apply the effect again.
Press Q to disable layer mask.
Create a new layer and fill the selection with white color.
Press Ctrl+T and scale down the layer vertically.
Place the layer at the top.
Select eraser tool. Erase the overlapping areas.