It's illegal for amateur radio operators to send broadcasts aimed at non-amateur listeners. What we do during communications emergencies is provide communications services for the authorities. This is provided most commonly by local RACES/ARES groups (http://www.arrl.org/chapter-4-ares-and-races), often associated with a local sheriff. I belong to such a group. A less common way amateurs can help is with local and long-distance message relays, using the National Traffic System (http://www.arrl.org/chapter-one-national-traffic-system).