As I've said before, clouds are lit from within; they are luminous; they glow, they flame. Watercolor is known for its luminosity. But compared with nature, it just lies there. Sing it does not.
I've talked about the problem of the rhetoric of painting in previous entries. What I'm doing here is trying to do some of this "effecting," through the use of complementary colors (the orange over against the blue, the purple against yellow), and also with contrasts of tone. I'm doing a poor job here with the latter - it's just so hard to get the paint dark enough!
What it comes down to is this: if you use those techniques well, you might be able to create a painting that suggests the effects of light you're trying to capture. But it's always going to be something of a trick for you to do that. Now how do you feel about that?
For myself, I just think that clouds are endlessly interesting and also permanently frustrating to try to capture.