'Human error' led to errant tornado siren during Denver thunderstorms, city says

Shelly Bradbury, The Denver Post on Jun 9, 2026

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DENVER — The errant tornado siren that sounded across Denver during thunderstorms Monday afternoon was caused by “human error,” a spokesperson for the city’s Office of Emergency Management said.

There was no technology failure or malfunction, Loa Esquilín García said in a statement Tuesday. Rather, one or more employees did not understand the protocol for sounding the siren, Esquilín García said.

“As a result, the city is implementing corrective actions, including a comprehensive review of alerting policies and procedures and enhancements to training and exercises for personnel involved in emergency alerting and warning operations,” the statement read.

Esquilín García noted in the statement that the sirens should not have sounded “as there as no tornado warning in effect for Denver at the time.” The spokesperson did not immediately answer follow up questions about exactly who made the mistake or how the protocols were misunderstood.

The false alarm sounded for about 5 minutes shortly after 4 p.m. Monday as thunderstorms moved through the city and during a tornado watch that covered the Front Range and much of the eastern half of the state.

The incident was the third time in five months that city officials accidentally sent out a Denver-wide safety alert. In January, residents across the city received a warning about an “active threat” near the University of Denver — an alert that was “broader… than intended,” city officials later said.

Then, in April, an alert about a robbery in the Ruby Hill neighborhood was again pushed out citywide; police said it was “inadvertently sent out further than intended.”

In a comment on social media, the Office of Emergency Management said Denver residents should expect to receive an alert on their cellphones in addition to the city’s sirens “during an actual” tornado warning or destructive thunderstorm warning.

“Because (Monday’s) siren activation was inadvertent and no warning was issued by the National Weather Service, no phone alert was sent,” the comment noted.

Greg Heavener, a warning coordination meteorologist at the National Weather Service in Boulder, said Tuesday that people who receive weather warnings or hear sirens should take a few moments to verify the alert with official sources before taking shelter.

The concern with false alarms, he said, is that people eventually start to ignore all alerts, even those that warn of real danger.

“I can’t say at what number of false alarms people start tuning them out,” he said. “But we are in the prime-time severe weather season in Colorado. So if people start ignoring alerts now, it could pose a greater life threat to them. We are getting to that peak. Storms, tornadoes, flash floods are going to continue to increase across the region.”

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