Just to make it a bit stronger I'd try what I'm doing right now, which is playing with the image in Photoshop, using levels layers just for fun. Check out selecting rectangular areas and "refining edge" with quite a big number, then opening an adjustment layer and playing with the histogram sliders to see what happens. Dodge/burn the clouds: you'd be surprised at what happens! There's a magazine in the UK "Digital Photo" which does a huge amount of Photoshop CS3/Elements and Paint Shop Pro skills training. I expect there's something similar where you are if you're not in the UK.
