Current questions and answers regarding the map editor.

Is it possible to add rain to a map somehow? I've seen something similar somewhere.

If you go through all the lighting options available in the map properties list, it seems that one or more of them had rain (you need to reload the map using the Reload Map button after changing the lighting). Once you find it, you can explore the lighting parameters in the properties tree (the GroundAmbientLights section) and see how the rain was implemented. In particular, lighting has a Rain parameter that requires a reference to an effect.