Cant believe no one has commented, lol. Well what your looking for is on the asset store *both free and paid). Theres lots of weather and time of day assets that are great. The problem i see is, if you add all those features in, and add PPE and other lighting/effects, its gonna hurt bad, fps/ms-wise.
Heres 2 examples:
Global Snow: this asset does what your asking (overhangs dont get snow, etc.), and performs insanely well. Dont know if its still available, as ive had it for years.
RainMaker: another great asset that more than does the job performantly.
What ever you choose to use, make sure its performant, alot of these type systems are hogs on fps/ms.