The problem with prayer.

[Angrboda]

To clarify: to say something is supernatural, by your definition, is to claim it will never be explained. [with by natural causes]

-my edit-

Exactly right. It is by definition excluded. The question is whether all phenomena can be explained by mechanistic natural processes that are reducible to small scale primitives. Even if something isn't technically supernatural, I think skeptics never seem to consider irreducible natural process that could exist at very high scales, some that may be deduced from conditions within the visible universe even if not directly observable within it.

All scientific theories are models. They are also examples of reduction. Explaining one thing in terms of smaller bits. At some level we are bound to come to a description of reality which can't be reduced. But we can never know definitively whether or not we are at the final reduction.

What irreducible natural process that skeptics never seem to consider are you referring to? I'm wary of the fact that you say it can be deduced but not observed. The same could be said for phlogiston and the aether.