As both Radar and Rain data layers are rasters, I'm not sure that rendering them together would be useful on UI map.
Moreover:
Radar data: real time observations in [Now-12h..Now], with validity step a couple of minutes Rain data: forecasts in [Now..Now+10d], with validity steps 1 hour thus these two data layers couldn't be contemporary (excepting maybe every full hour and only in the past)Generally speaking, overlay two data layers is great when when a vector data layer (e.g. pressure isolines) is rendered over a raster data layer (e.g. Wind in color shading mode).
When you overlay two raster data layers, you have to disable the layer on the top in order to see the layer on the bottom. Or well to play a lot with new transparency color of each of the layers, which is not trivial (as both of them have blue palettes in this very case)...
