"The vast majority of Joplin residents" did not respond to the first siren warning of the May 22 twister that killed 162 people because of a widespread disregard for tornado sirens, federal officials concluded in a report issued Tuesday.
"This was a warned event," Kathryn Sullivan, deputy director of the National Oceanic and Atmospheric Administration, told reporters, noting that several days before forecasters were warning of a strong possibility of twisters.
Officials didn't blame residents, many of whom complained that sirens often go off in Joplin for tests or even just when dark clouds form, and suggested that a "non-routine warning mechanism" be developed to make it clear when a siren should be taken seriously.
Keith Stammer, who heads the local county's emergency management agency, said the department issued two sets of sirens ahead of the tornado and that many people ignored the first siren.
Some people thought a second siren was an all-clear signal, which it wasn't, he said. Stammer said he has never issued an "all-clear" during his 18 years in the department.
"Honestly it was a bit of a disappointment that there were so many people who didn't move to shelter after the first warning," Stammer said. "The human side is the part that's most frustrating."
The nation's deadliest single tornado in six decades also damaged thousands of homes and injured hundreds of people.
The report was prepared by a team from the National Weather Service, a department under NOAA, that interviewed some 100 people in Joplin.
The team examined warning and forecast services before the EF-5 tornado cut through the southwest Missouri city of about 50,000 residents.
The team also reviewed the public's response to warning communications. NOAA said the team's goal was to identify what was done correctly and areas that could be improved.
Cleanup, recovery and rebuilding have been under way in Joplin since the tornado hit. Four schools were destroyed and six other district buildings were damaged. Entire neighborhoods were leveled, as was much of the city's main commercial district.
Preventing a similar tragedy remains a top concern. At a community meeting in August arranged by the Federal Emergency Management Agency, residents called for more community storm shelters in schools and other public buildings, as well as an improved storm warning system.
Doug Doll, regional president for Arvest Bank, said Monday he felt the warning systems in Joplin were adequate but that they could possibly be improved.
"About the only thing we can do to make it better is to add more sirens in strategic locations throughout the community that can be heard by everybody," he said.
Doll also recommended developing a way to alert major employers and let them know if a storm is coming. He said bank employees typically head to the vault in the event of a tornado warning. But the recent Joplin tornado hit on a Sunday when the bank was not staffed.