This is a limitation from engine. They are working on it.
Nope. Just working on material function for wetness/snow while waiting for some answers from epic about some limitations.
Also working on a Scene to show Rain/Snow and Lightning effects.
The bad news, is I will not post updates until next month. My second son is coming and I am busy with it.
The good news, next month start my vacations (when my son was born) so I will have a lot of time to work on this.
Remember, Im just a hobbist.