Outdoor Warning Sirens | Johnson County Kansas

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Outdoor Warning Sirens

Tornado Siren

Johnson County’s outdoor warning system consists of 190 sirens placed strategically throughout the county as an early warning device to alert citizens to take shelter and seek additional information.

While the outdoor warning system can be an effective method of notifying those outdoors, it is only one component of a comprehensive emergency warning system including the use of NOAA weather radios, the Emergency Alert System, and emergency notifications from local media.

Designed as an outdoor warning system, the sirens should not be relied upon to provide sufficient warning indoors or in noisy areas. Air conditioning, thunder, wind, rain, and other conditions can cause the sirens not to be heard indoors or outdoors (even if sirens can be heard during tests).

Sirens are also subject to lightning strikes and other equipment malfunction. For these reasons, everyone is encouraged to have multiple ways to receive information about severe weather.

Understanding Outdoor Warning Sirens in Johnson County

Outdoor warning sirens in Johnson County are part of a public safety system designed to alert people who are outdoors to take immediate shelter during life-threatening emergencies, most commonly tornado warnings. These sirens are not meant to be heard indoors and should not be relied on as your only source of emergency alerts.

Sirens in Johnson County are activated based on polygon warnings issued by the National Weather Service (NWS). A polygon is a specifically drawn area that shows where a tornado is expected to impact. When the NWS issues a tornado warning, only the sirens located within or near the warning polygon will be activated. This ensures targeted, accurate warnings for those at greatest risk while reducing over-alerting in unaffected areas.

What are polygons?

Polygons are digitally drawn shapes used by the NWS to pinpoint areas under threat from a tornado. They are based on radar data and storm movement and allow for more precise warning activation. Only sirens within or near the polygon will be activated, reducing unnecessary alerts and enhancing the relevance of the warning.

Explore the Interactive Siren Map

To provide more detailed information about siren locations and coverage, we encourage you to explore our interactive AIMS siren map, where you can zoom in and see:

• Exact siren locations
• Approximate coverage areas (siren buffers)
• Neighborhood-specific visibility

AIMS Interactive Map

Testing

The outdoor warning system for Johnson County is tested at 11 a.m. on the first Wednesday of the month. Tests can be postponed for two primary reasons:

1. Extreme cold, freezing rain/drizzle, and/or icing might damage the equipment.
2. There is severe weather (or potential severe weather) occurring in the local area and activating the outdoor warning system might cause confusion as to whether the activation is a real event.

If it is determined that the monthly test will be postponed, the test will be rescheduled for the second Wednesday of the month at 11 a.m. If it is determined that the monthly test is unable to be performed on the second Wednesday, the test for that month will be canceled. The next test will then be the regularly scheduled test on the first Wednesday of the following month at 11 a.m.

In March, the siren test may be performed on the first Wednesday in addition to the activation of the system as part of a statewide tornado drill during Severe Weather Awareness Week and in conjunction with the National Weather Service. These drills are typically conducted on a Tuesday or Thursday (back-up date) afternoon, late enough as not to disrupt the school lunch period.

Activation

The cities within the county own and maintain the sirens within their cities. Johnson County Emergency Management has the primary responsibility to activate the sirens throughout the county. In addition, the cities of Lenexa, Olathe, and Overland Park have the capability of activating their own sirens if they so chose.

There are three basic criteria to activate the sirens for tornadoes:

• The National Weather Service issues a Tornado Warning for Johnson County,
• A county trained and certified weather spotter reports a tornado; or
• A tornado is reported by a local public safety official.

Johnson County has the capability of activating all of the sirens at once or by activating one or more of five established siren zones. All sirens are sounded unless the threat is clearly confined to an individual zone (or zones). During a tornado warning, the sirens will be sounded for a three minute duration in ten minute intervals (three minutes on, seven minutes off) for as long as the tornado warning is in effect. There is NO “all-clear” siren.

Frequently Asked Questions

Why didn’t I hear a siren during the last storm? If you were outside of the NWS warning polygon, sirens in your area may not have been activated. Sirens are intended for outdoor alerting, and they may not be audible inside homes and buildings. Background noise, wind direction, or weather conditions can impact how far siren sounds travel.

Are sirens my only way to get alerts? No. Sirens are just one tool. We strongly recommend having multiple ways to receive emergency alerts, including:

• NotifyJoCo alerts (sign up at notifyjoco.org)
• NOAA Weather Radios
• Local news and weather apps

What are polygons and why are they used?

A polygon is a targeted area drawn by the National Weather Service (NWS) during a warning. Johnson County activates sirens based on the polygon rather than entire jurisdictions or counties. This:

• Reduces false alarms
• Limits public desensitization
• Targets those most at risk

What are siren zones, and are they still used?

The blue grid zones you see on our map on AIMS represent backup activation zones, which can be used if:

• The NWS system is unavailable
• Manual activation such as a spotter identified tornado
• Communication or software limitations prevent polygon-based activation

Each zone includes a set of sirens that can be activated together. These zones were historically used as the primary method of activation but now serve as secondary tools for system redundancy and continuity.

How do I know which zone I’m in?

The zone map is available on our website for reference. While zones are no longer the primary activation method, you can still view your zone as part of our backup planning and system redundancy.

When are sirens tested?

Outdoor warning sirens are tested on the first Wednesday of every month at 11:00 AM, weather permitting. If inclement weather is present or expected, testing is postponed to the second Wednesday of the month at 11:00 AM to avoid confusion with an actual event.

Will I always hear a siren if there’s a tornado?

Not necessarily. You may not hear a siren if:

• You’re inside, especially with windows closed or you are in a noisy environment
• You’re outside the defined area of risk

Siren activation is based on where the warning is, not where the storm might go later.

Siren Resources

Warning Siren Map What To Do When You Hear a Siren