I hope all is well. I know here at Fahlgren we have emergency notification through text messages. Although it wasn't an emergency, during the February snowstorms a designated person relayed to all of us if the office was going to be open, how to determine if you should come in, etc. Some of this was based on snow emergency levels in the different counties that employees live.
Other groups I've been involved with use an intranet to notify internal audiences. In crisis planning, many groups will set up a microsite that can be prominently inserted to the front of a group's home page with information.
Hope this helps,