The United States Department of Homeland Security has launched the National Terrorism Advisory System to replace the color coded Homeland Security Advisory System in place since 2001. The new system is simpler to understand with only two categories for alerts: Elevated and Imminent.
An Elevated Threat warns of a “credible terrorist threat against the United States,” while an Imminent Threat warns of a “credible, specific, and impending terrorist threat against the United States.” The alerts will contain information specific to that alert with information on personal safety, etc. More information can be found through the Department of Homeland Security as well as the Arizona Emergency Information Network.
More information on emergency preparedness can be located here.