I'm envisioning a creature or plant that consumes magical energy, and which produces localized rainfall as a byproduct.
If the consumption of this magical energy produces localized effects related to light and electromagnetic radiation, how might condensation result from that side effect?
Or, to put this another way: What changes to local electromagnetic radiation (such as heavy sunlight, gamma rays, etc) would cause liquid water to condense from a semi-arid atmosphere?
Here's what a sample answer might look like:
[Unobtanium] rapidly cools when exposed to [Alpha particles]. If exposed to heavy concentrations of [Alpha particles], condensation would form on the surface of [Unobtanium deposits], and a plant with high concentrations of [Unobtanium] would drip liquid water if it were being constantly bombarded with [Alpha Particles]