People that have social media can create their own alerts. School systems where I live have wide reaching alert systems in place for closings delays and emergencies. Creating a NATIONAL system sounds like another multi trillion dollar FUBAR web system creation to me and to all of my friends. Several public announce,nets to get people to link in to your basic system should suffice. Word of mouth will prep as your system around or in the event of an emergency word will still get around. If the disaster is such as an IMMEDIATE CRYSIS not everyone is going to be connected to the net at all times anyway.