I pretty much agree with Forlorn Willow: the tone and writing are solid, in the 8-10 range, but the concept does basically nothing for me as-is. I might even go lower than 4/5 for concept and scariness, since it takes a full 20 minutes of continuous cloud watching for the effects to even begin, and I can't imagine that's going to happen very often. It doesn't seem like anything that's likely to happen to me (even if I were in the right geographical area, I doubt I've ever spent that much time watching clouds in one sitting); even if it happens to other people, it's still pretty unlikely to affect me; it doesn't have a particularly interesting or coherent central metaphor; and it doesn't have a non-horror hook at all (like being funny, pathetic, or adorable). As it currently sits, I'd downvote.
That said, there's no reason it couldn't be built into something that worked better. There is a seed of a good SCP in there somewhere, and the writing's competent enough to succeed if paired with a good idea. I'd advise aiming weirder, not necessarily scarier.