To go for "portrait style" in landscape photography always is a deliberate step out of the usual, and I like that you took it for this one so you'd be able to frame the opening in the clouds that goes right down to that tree on the shore. So apart from the colours, which I happen to just love (surprise-surprise, I know :er: ), I really like these dynamics in your photo!!!
Yeah, that is quite a fantabulous photo there. I think photography shouldnt be tied down to conventions etc. so it is great that you opted for the portrait format in this case. Even if the sky didnt have such interesting clouds this portrait format would have been the best. Good choice.