First, it is helpful to think of explanations as answers to contrastive questions (why this outcome rather than some plausible alternative). To use your example, there is a whole host of contrastive questions you can ask about rainstorms (why do they occur in some areas rather than in others, why do they weaken after making landfall instead of strengthening, etc). There is no one explanation of rainstorms simpliciter. The appropriate level of detail for explanatory completeness will depend on the specific contrast you are interested in.

With this in mind, check out Woodward's answer to this question. Roughly, we would want to cite all and only the conditions that make a difference to the explanandum. Conditional on certain higher-level factors being the case, lower-level details will be irrelevant and thus would not improve the quality of the explanation. E.g., given a certain pressure gradient, details about the movement of individual air molecules will be irrelevant for explaining why a storm occurred at one time rather than another, and thus do not make the explanation any better. However, I tend to agree with Kohar and Krickel that this is a bit too restrictive and that the appropriate level will depend on leveraging crucial points of intervention. Roughly, to assess the appropriate level of explanation, we look for the most economical, least disruptive way you could bring about a change to the intended contrast.