Last November Google added a weather layer which included a global cloud layer, and weather radar for the US. Today Google has expanded the radar layer coverage to include: Europe, Canada, Alaska, Hawaii, and Puerto Rico. (The European coverage is limited to the north central part of Europe.) The new weather radar data once again comes from Weather.com. You can find the new weather information under the Weather layer on the lower left of Google Earth like this:
If you open the Weather layer folder, and click on the Information placemark, you can load a 6 hour radar animation as well.
There’s another weather site which has some great Google Earth weather files called GuiWeather. They have a weather radar visualization for the US which I think looks even better (higher resolution for one thing). And they have a radar animation built-in to the same file.
See also NOAA Radar data in Google Earth here, and here.