Outdoor Warning Sirens

About the Sirens


The Sirens are activated from McLean County Emergency Management Agency (EMA), with a backup at MetCom. EMA has a network of trained weather spotters that are activated when severe weather conditions arise. The Bloomington Fire Department supplies one of these spotters and this person is positioned on the upper floors of State Farm's Downtown Building. Normal Fire Department has a spotter on the top floor of Watterson Towers on ISU Campus. These spotters, in conjunction with ground spotters and other emergency resources communicate with MetCom and EMA.

Typically reports of funnel clouds are verified by a spotter or other creditable agency representative before the sirens are activated. It is important to realize that during a severe weather incident like this, it is typical to get hundreds of reports of funnel clouds all over our community. It is important that these are confirmed, as most of these reports turn out to be negative. If the sirens were activated for any report, you would find that they would be sounding constantly through an entire thunderstorm event. This would make them ineffective as people would ignore the warning.

The agreed upon approach is that the sirens are to be used to alert citizens who are outdoors during the imminent hazard and prompt them to seek additional information on the threat (timing, location, and severity) to allow sufficient time to seek proper sheltering.

Activations Conditions


Siren activation recommended for:
  • Tornado Warning -- Issued by the National Weather Service or Tornado or funnel cloud indicated on radar, reported by a trained spotter (Law Enforcement, Fire Department or Emergency Management officials).
  • Severe Thunderstorm Warning -- Issued by the National Weather Service and Winds 70 mph or greater forecast or occurring.
There will NEVER be an "All Clear" signal from the outdoor warning sirens. People in or near the warned area should then monitor reliable sources such as NOAA All-Hazards Radio or local media services to know when the threat has dissipated.

Remember: Outdoor warning sirens are there to warn people OUTDOORS -- Outdoor warning sirens are designed for alerting people outside their homes and away from other media sources of imminent danger from an approaching storm. It is designed to warn these people outside to take cover immediately. The sirens are not designed as a consistent warning system for persons inside of structures.

While sirens can be heard inside, there are a variety of factors that can influence someone's ability to hear the siren, such as topography, obstructions between the siren and the structure, construction of the building or residence, other noise sources (TV, radios, hail, wind, etc), and distance from the siren. The City of Bloomington has 19 outdoor warning sirens, Normal has 11 and Bloomington Township has 1 at Crestwicke. The sirens are designed to have a 1.5 mile coverage area based on the decibel level per the manufacturer. When EMA determines that siren activation is necessary, all sirens in the system are activated. We do not activate sirens in specific areas only.
Individuals are responsible for monitoring conditions for their personal safety. The National Weather Service has created a warning system that consists of Watches and Warnings for a variety of weather conditions to keep people informed. These informational watches and warnings are broadcast over TV and radio. When weather systems approach, people should monitor either TV or radio to keep up to date on the conditions. Weather alert radios are designed to receive broadcasts from the National Oceanic and Atmospheric Administration (NOAA) thru the National Weather Service (NWS). These devices only broadcast weather information and are a valuable tool for monitoring severe conditions and are available in both desktop and portable units.

It is also important for individuals to understand the NWS Warning system. A Watch (Severe Thunderstorm or Tornado) means that conditions are right for these type of storms to occur. During a watch, people should monitor conditions and be prepared to take shelter. A Warning means that the severe weather is occurring in the area (Thunderstorm or Tornado) at this time, people should seek shelter immediately. People should not wait until the sirens are activated or a tornado is actually sighted in their specific area as this is too late. A Warning is the time when people need to be in a protected place monitoring conditions until they improve and the situation passes.

Monthly Testing


As with any system, some failures do occur. We test the warning sirens once a month, on the first Tuesday at 10:00am. If there is inclement weather, the test will be postponed or cancelled. The redundancy of the system allows for outdoor users to hear sirens even when one closer may not sound, but this is also why it may not be heard indoors.