Here are the sized-down idea pictures.
0294 threshold120.jpg
0294 threshold144.jpg
0294 posterize16.jpg
0294 posterize5.jpg
0294 equalize invert posterize12.jpg
I took a bunch of cloud pictures that you're welcome to use for textures, etc, which I'll add below, but first, some ideas for jumping off points from this original image:
0294 original.jpg
I ended up having to size it down a little, so it would fit the upload limit for the site... so the results might be slightly different if you copy the filter settings exactly on this original (it's 300ppi, 8x12"), but hopefully not too much, and I'm sure you'll do your own thing. These are just quick ideas, anyway. I used ps, but I think the filters are the same/similar for gimp if you use that instead.
The file names tell you what steps I took to get the individual looks.
Here are the sized-down idea pictures.
0294 threshold120.jpg
0294 threshold144.jpg
0294 posterize16.jpg
0294 posterize5.jpg
0294 equalize invert posterize12.jpg
Another one I played with, a lot. Didn't keep track of the numbers, but the basic filters are in the file name, which I'll type out in case you can't see it. It's also only sized down 50%, so still somewhat usable as is.
0302 original.jpg
0302 posterize gradientMap hueSat levels colorBal bwWtint levels.jpg
0302 posterize gradientMap lessSat levels colorBal bw(with)tint levels.
I was aiming for a sort-of height map type of thing... and if you invert it, it turns blue and is very reminiscent of an ocean's, or lake's, bathymetry.
And some more originals... each 300ppi, 8x12".
0295 original.jpg
0297 original.jpg
0298 original.jpg
0300 original.jpg
0263 original.jpg
0268 original.jpg
0273 original.jpg
0275 original.jpg
0278 original.jpg
That's probably enough for now. There are so many ways to interpret a cloud. =)