I used to be able to do this with the Old World Editor. I fell upon it quite by accident, in SFX sound emitter section of the old editor tabs (in the right hand column). How do I find the rain sound(s) in the New World Editor? Thanks.
I believe I fell upon it quite by accident. You have to hit the add button and another row of tile buttons opens up below the main row. There you can create a sound source, light points, etc. I more or less answered my own questions. I can make lightning and the sound of rain. Only thing missing is thunder. I hope they add a weather engine, so that it doesn't have to be completed manually, but in the meantime, not a bad sequence to achieve the desired results.