OK, my two cents. unless they got ahold of a warhead from the china or the former soviet union, it would most likely be a clunky device with highly unpredictable performance. Either way the point is terror, so they will target areas that most represent the U.S. Like they did with the world trade center. That being said, look for cities like New York, Chicago, and LA. If you live in the larger metropolitan areas you may have an immediate concern, however if not you should have time to move out. If it's your town you probably won't have time to react. If not you have to assess the situation and make your decisions accordingly.