Try the attached kmz file which I've created from the NOAA website for the Chicago area (multiple radar images included) or use the GUI Weather radar kmz. They both should provide great coverage of your area.
Edit: Excuse me Ben, I thought you are using the 3D version. The files listed will work in the 3D version only.
Edit 2: The file is back. As mentioned, you can easily create your own kmz files on the NOAA website. However, currently all for the US only. Wish there would be some kind of these images available for germany...