Why did I hear a tornado siren? How Kansas City’s extreme weather alerts work

For the past week, the National Weather Service in Pleasant Hill, Missouri, has issued three tornado warnings across the metro. On the morning of April 27, residents in Cass County woke up to heavy winds, hail, and sirens.

Hallie Bova, meteorologist with the NWS, said that last week, the area had multiple rounds of severe weather, including the threat of tornadoes.

"We’ve seen multiple tornado warnings across Kansas and Missouri,” she said. "This is not outside the realm of normal for this time of year.” She said back-to-back tornado warnings are common.

Annie Poelzl, Director of Clay County Emergency Management, said with those back-to-back warnings, there can be confusion, and sometimes a malfunction, when the sirens activate.

“The sirens are also susceptible to technological failures, like any other piece of technology,” Poelzl said. “We always want to tell people there other ways of receiving those warnings.”

Including the sirens, Poelzl said people should avail themselves of these multiple ways to get alerts about tornadoes: National Weather Service information via their local news, radio broadcasts and text alerts through your phone.

During last week's storms, many residents took to social media to ask why sirens went off in downtown Kansas City, or elsewhere, when there were no sightings or reported threats of a nearby tornado.

Jackson County Executive Manny Abarca generated a flurry of commentary with a social media post suggesting sirens causes unnecessary alarm when there is no tornado threat in the area.

How sirens work

Each municipality and county uses their own criteria to determine where and when to activate sirens. In Kansas City, these judgments are made by the Office of Emergency Management. Lane Johnson is a spokesperson for Kansas City, Missouri.

“Tornado sirens in Kansas City are activated by designated warning zones,” Johnson said. “Unlike wireless emergency alerts that can be targeted by individual cell towers, the city cannot precisely refine siren activation areas to match the exact NWS tornado warning polygon.”

NWS warning polygons are geographic areas drawn to indicate the precise location of a severe weather threat, such as a tornado or thunderstorm. They provide the NWS a mapping strategy to pinpoint areas under a tornado threat.

Kansas City maintains over 100 sirens within its limits. The sirens, when activated, will sound for approximately 10 minutes. If the sirens go off again after that period, another tornado has been spotted. But Johnson says that the second funnel cloud may be miles away.

“Upgrading the siren system to allow activation only within the exact NWS tornado warning polygon would require significant infrastructure changes,” Johnson said. “We recognize that sirens may occasionally sound in areas that are not ultimately impacted by a tornado. Public safety remains the priority, and it is preferable to alert people to the possibility of danger rather than risk the public's safety.”

In Clay County, both the county and some cities are responsible for activating sirens. The Emergency Management department of the county maintains eight sirens, which cover cities such as Smithville and Holt. Sirens in Kearny, where the April 23 funnel touched down, are managed by the city.

“The policy we use for Clay County is that anytime the wind reaches 73 mph or higher, that is when we trigger setting off those tornado sirens,” Poelzl said. “And we only set them off by those zones, so if we set off the north zone, they go off by Smithville Lake and Holt.”

Poelzl says zones or sections can have multiple sirens. Unlike Kansas City’s, Clay County sirens are on a three-minute loop until the tornado threat has passed. It’s not uncommon, Poelzl says, for those in areas less impacted by the threats to hear sirens going off.

Johnson County, Kansas, maintains a total of 190 sirens and, like Kansas City, uses the NWS map to pinpoint areas under tornado threat. Only sirens within that area will be activated, limiting the alerts and increasing the warning reception, but they also could sound in unaffected residents.

Hallie Bova said even though sirens may not be referencing tornado activity in your neighborhood, it might be close by or moving quickly. She urges residents to be safe and take cover anyway. Even the most detailed predictions about how severe weather behaves can be wrong.

“Even though the threat is not immediately over your area, it's better to be safe and take precautions just in case something does happen.”