Outdoor Warning Siren Activation

To establish common guidelines for activation of outdoor warning sirens throughout the Polk County / Des Moines Metropolitan Area.

Confusion hinders public response. Using common / consistent guidelines for the outdoor warning sirens throughout the various jurisdictions of the Des Moines Metro Area / Polk County minimizes confusion in emergency situations. Establishing common guidelines will also enable communities to partner in an area-wide public education campaign regarding sirens and the overall public emergency notification system.

These guidelines are based on communication technology and systems available in the Des Moines Metro Area / Polk County and on the current science of severe weather warnings.

The outdoor warning sirens represent only one part of a broader public emergency notification system. Other components might include: NOAA All-Hazards Radio, law enforcement, direct dialing / automated notification systems, and the media. Sirens are used to alert citizens who are outdoors of an imminent hazard and prompt them to seek additional information on the threat (timing, location, and severity).

This document is not intended to relieve, replace, or supersede any authority or responsibility local jurisdictions might have to protect the citizens of their community.

Activation Conditions:
Siren activation recommended for:

1)  Tornado Warning
     a. Issued by the National Weather Service
     b. Tornado or funnel cloud reported by a trained spotter (law enforcement, fire department official, emergency management agency)

2)  Severe Thunderstorms
a. Issued by the National Weather Service
     b. Winds 70 mph or greater forecast or occurring

Warnings are officially issued by the National Weather Service (Johnston, Iowa) and are received at all three Public Safety Answering Points (PSAP) / 911 Communication Centers in Polk County. The official warning is received via the Metropolitan Incident Command Radio Network (MICRN) and the National Law Enforcement Telecommunications Systems (NLTS).

National Weather Service warnings define the area threatened by the storm and include information about the history and / or potential of the specific storm. In addition, trained spotters such as law enforcement, fire, and emergency management officials may provide real-time reports of an imminent threat approaching or occurring in the community. When a warning includes the specific hazards defined above or when trained spotters report any of these hazardous conditions, sirens should be activated for all jurisdictions in the threatened area. Because of technology limitations and the configuration of siren activation systems, there may be areas adjacent to the threatened area, but outside the official warning boundaries that are warned as a precaution. People in or near the warned areas should always seek additional information from reliable sources such as NOAA All-Hazards Radio or the local media.

Activation Duration:
When activated, the tone should be sounded for 3-5 minutes, re-sounding every 10-15 minutes for the duration of the threat (warning period).

All Clear:
There will NOT be an "all clear" signal from the outdoor warning sirens. People in or near the warned area should monitor reliable sources such as NOAA All-Hazards Radio or local medial to know when  the hazard threat has dissipated.

Outdoor warning sirens shall be tested on the first Saturday of each month at 12:00 pm (noon). A "growl" test may be performed on the third Saturday of each month at 12:00 pm. A "growl" test activates the system without the full audible alert.

If a severe weather watch or warning is in effect for the Polk County area prior to 12:00 pm on a scheduled test day, the sirens should not be tested that day. Outdoor warning siren tests will resume on the next scheduled monthly date.

Testing may be suspended during the winter months (December - February) when ice or sub-zero temperatures could damage the siren system. Testing should be considered condition-dependent during these months. Testing schedule should be maintained whenever possible for continuity purposes as well as system reliability.

If testing is required at any time outside of the normal monthly testing schedule, Polk County Emergency Management Agency shall be notified. Polk County Emergency Management Agency will then notify the media to better ensure awareness by the public of the additional testing and hopefully reduce the number of concerned callers to the Public Safety Answering Points (PSAP).

Purchase, installation, ownership, and maintenance of the siren are the responsibility of the local government jurisdiction in which the siren is physically located. Other ownership and maintenance relationships may exist between public or public / private entities but shall be expressly documented and agreed upon by parties involved in the agreement.

Related Documents:
For additional supporting information, please refer to:
1)  Outdoor Warning Siren Activation Quick Reference Guide  (PDF)
2)  Outdoor Warning Siren Activation Frequently Asked Questions (FAQ)


Outdoor Warning Siren Activation Guidelines