Outdoor Warning Siren System


An Outdoor Warning Siren (OWS) system consists of siren(s) designed to alert people of approaching or existing hazardous conditions, which will require immediate protective actions in order to save lives. Traditionally, these systems have been mistakenly referred to as “tornado sirens” but the term fails to acknowledge all applications for activating sirens. In order to avoid any confusion as to the purpose of these systems, the City of Midlothian shall refer to sirens as “Outdoor Warning Sirens” in an effort to reinforce the multiple conditions for which the City of Midlothian may activate sirens to alert people in outdoor areas.

Outdoor Warning Sirens

Reasons for Activation

The City of Midlothian may use the Outdoor Warning Sirens to alert and notify people in outdoor areas of emergency situations. Although the typical use of these systems has been to notify people of potentially dangerous weather conditions, there are several reasons why public safety personnel could activate outdoor warning siren systems. Some of these reasons include:

• Severe Weather capable of producing effects that are hazardous to persons or property 

• Local Warning Point (the Northern Ellis Emergency Dispatch) activities in coordination with the National Emergency Alert System 

• Hazardous materials released into the atmosphere 

• Catastrophic emergencies that pose an immediate threat to safety (i.e. dam failure) 

Activation Considerations

The City of Midlothian conducts routine public education activities in order to ensure the purpose of the OWS system and proper response to OWS activation is understood to the greatest extent possible. The City of Midlothian may consider activating the Outdoor Warning Siren Systems when the following conditions are observed or predicted in their area:

• The National Weather Service (NWS) issues a Tornado Warning. The Outdoor Warning Siren System will automatically activate when the National Weather Service issues a polygon for the tornado warning to include the City of Midlothian. The Outdoor Warning Siren System will activate for three (3) minutes to provide warning to the community. There may be times that the City activates the siren system more than once to provide advanced warning, when possible.

• The National Weather Service Issues a Severe Thunderstorm Warning and indicates the potential for destructive winds of 70 mph or greater (sustained, not wind gusts). 

• Trained storm spotters have reported a tornado in the jurisdiction, or in a neighboring jurisdiction that has the potential to affect our community. 

• Observed hail of 1.5” in diameter or greater. The size of hail that warrants outdoor warning siren activation may be adjusted at the discretion of local officials in the event of special situations such as large outdoor public gatherings where the potential for injury is increased. 

• Other emergency as directed by the community’s designated public safety officials.

Notification of Activation

The City of Midlothian makes external notifications to neighboring jurisdictions, the National Weather Service in Fort Worth, and additional partners as soon as possible indicating the Outdoor Warning Siren System has been activated. Doing so allows regional partners to understand the nature of the activation and to anticipate if the conditions that necessitated the activation will apply to neighboring jurisdictions. The City of Midlothian also utilizes the National Weather Service Chat tool to share this activation information due to the intersectoral audience that monitors the site. Additionally, during National Weather Service requested amateur radio net activations, the notification can be conducted by making an announcement via the net in progress or other means available.

System Considerations

The City of Midlothian has rotating electronic and mechanical sirens. Rotational sirens typically employ a single output that rotates for the duration of the siren activation. 

Sound propagation is affected by several factors such as vegetation, obstacles, and the insulating factors of homes, buildings and vehicles. This greatly affects the ability of people inside buildings or vehicles to hear the Outdoor Warning Siren System when activated. Therefore, it is important to know that the Outdoor Warning Siren System’s design is intended to ensure that persons who are outdoors should be able to hear the sirens. This means that persons who are indoors may not necessarily hear the sirens in their area and should utilize other means for notification such as NOAA Weather Radios, Wireless Emergency Alerts, MidlothianSafe Alerts, Emergency Notification System, radio and local television media for emergency notification.

Monthly Testing

The City of Midlothian tests the Outdoor Warning Siren System on the first Wednesday of each month at 2pm. The siren test will occur for a one (1) minute test to ensure that the sirens are functioning properly. The Outdoor Warning Siren System will not be tested during periods in which overcast, severe or inclement weather is possible, so as to avoid confusion between actual weather events and testing. The City of Midlothian also conducts daily silent testing to ensure systems are functioning properly as needed.

Monthly Siren Test