Where it works
BeamWeather reads NEXRAD. That is the United States, Puerto Rico, Guam, Alaska and Hawaii — and nowhere else.
159 WSR-88D sites and 45 terminal Doppler radars, 204 in all. Pick any of them, anywhere in the country, from anywhere in the world.
A map of the United States and its territories with a mark at every NEXRAD radar site.
What it isn't
No forecast model, no satellite, no international radar, and no data that isn't NEXRAD. If you are outside the United States you can still watch American storms, and that is the whole of it.