Deciding whether to issue a warning or other emergency alert can be a difficult decision. Ultimately it will be a matter of local judgement; however, it will be helpful to have an outline of decision criteria to assist you with the process. Your State or Local EAS Plan may provide criteria for activating the Emergency Alert System, and if so, should be incorporated into your local planning.
The following criteria are derived from National Weather Service definitions and practice. The decision points below are illustrated in Job Aid #2, Warning Decision Tree flow diagram.
Warning or Other Emergency Alert?
Assuming you are starting from an occurring or impending potentially hazardous event, the first question is whether or not the event meets the definitions for warning or emergency first described in Chapter 2.
"Warning messages are issued for those events that alone pose a significant threat to public safety and/or property, probability of occurrence and location is high, and the onset time is relatively short." From this definition, the following criteria may be derived:
Does this event pose a significant threat to public safety and/or property?
- Is the probability of occurrence high?
- Is the location well defined?
- Is the onset time relatively short (within the maximum 6 hour duration of an NWEM)?
- If the event fails to meet the criteria for issuing a warning, then consider whether the event meets the criteria for another type of emergency alert.
- "Emergency messages are issued for those events that by themselves would not kill or injure or do property damage but indirectly may cause other things to happen that result in a hazard."
- Does the event meet the description of specific purpose NWEM emergency alert types such as Telephone Outage Emergency, Child Abduction Emergency, Avalanche Watch?
- If not, does the event constitute a Local Area Emergency or qualify for a Civil Emergency Message?
- If the event fails to meet the criteria for either a warning or other emergency alert message, consider other means of dissemination.
- Is it Night?
Assuming that the event does meet NWEM criteria, the next criteria to consider is time of day.
- NWEMs are not only broadcast over NOAA Weather Radio, they will also cause the NWR alarm to sound. Therefore, only the most imminent and hazardous events should be issued during nighttime hours, generally after 10:00 PM and before 7:00 AM local time. (Consult your Weather Field Office for guidance as to local practice.)
- Generally speaking, only those events meeting the criteria for warnings should be considered for nighttime broadcast. Other emergency alerts should be reserved for daytime broadcast.
- Finally, assuming that the event meets the general criteria for a warning, the final criteria should be whether the threat is severe enough, over a large enough geographic area, and the protective instructions useful enough, to warrant waking a sleeping public.
Refer to Job Aid #2 for a Warning Decision Tree diagram. Then check your knowledge via the self-assessment quiz on the next page.
 Job Aid
Job Aid, Warning Decision Tree |