Detect it. If the weather modification is an interference with normal physics then it is a technology that is used across the other side of the galaxy.

If our divine hosts have the tech to do that, and I assure you they do, then I would guess they wouldn't allow themselves to be detected as it would interfere with your moral agency.

The only thing we need to know is why they might use it, and the answer to that would be that people would be guilty of serious transgression.

There is no need to detect a technology we can prevent the use of through obedience.