Hello Dan,
thanks for your assistance!
I have tried your suggestion, but with no luck. First, I can't seem to directly save a NumPy array as a tif, using a.save().
Saving the tiff outside of my geodatabase after I converted it to a raster creates a tiff file that is solid black when previewed in the windows explorer.
But when I add the raster to ArcMap, I have the same problem as initially: the raster is invisible, and appears to have only NoData values. When I set the symbology to display NoData as a certain color, the whole raster will have this color.
I don't think it is a problem with the extent or projection, because NumPyArrayToRaster should take care of those and I keep my settings consistent. After all I was already able to see the raster at the right place with the right size, but only after I displayed the NoData values as a certain color.
What I noticed is that the high and low values seem to be off in the symbology of the raster...