NORMAN, Okla. (AP) -- Event organizers have learned the hard way that the usual half-hour warning of severe weather might be enough for people in their homes, but it's not enough to clear people from big venues where concerts and football games are held.
Seven people died and more than 40 were injured at the Indiana State Fair in 2011 when a sudden 60 mph gust knocked a stage onto a crowd waiting to see the band Sugarland perform. In 2009, high wind toppled a canopy at a Dallas Cowboys practice facility, leaving one person paralyzed and 11 others less seriously hurt.
"Like 9-11, it takes a really bad thing to get our attention," said Harold Hansen, the life, safety and security director for the International Association of Venue Managers. "The rules changed."
The incidents prompted venue managers to move their annual storm-preparedness meeting to the National Weather Center in Norman, Okla. — the heart of Tornado Alley and the forecast centers that watch it.
"Now some of the heavy hitters are getting involved," said David VandenHeuvel, a senior vice president with Weather Decision Technologies, which has provided forecasts to about 150 events in the past 1½ years.
The conference had about a dozen participants when it started five years ago. This year, more than 40 emergency managers and event operators came, including the NFL and the Country Music Association.
Through lectures about weather watches, lightning, crowd dynamics and shelter readiness, the experts repeatedly stressed the need to have a plan before the weather turns bad.
"They're waiting for a warning to be issued," said Kevin Kloesel, associate dean of the University of Oklahoma's College of Atmospheric and Geographic Sciences. "The message over the two days here is: if you wait until that point, you are not going to have the time. If you wait for the warning, it's too late."
The list of close calls is chilling. A 2010 tornado shredded the roof of a Montana sports arena packed with thousands of people the day before. A lightning bolt struck 500 feet from the Texas Rangers pitcher's mound during a game in July 2012. Pennsylvania's Pocono Raceway was struck by lightning the next month, three minutes after a race was canceled.
Jim Digby, who managed world tours for the rock band Linkin Park, attended last year's conference and has since formed the Event Safety Alliance. That group has suggested adopting procedures based on specific weather conditions, such as wind speed.
Digby told The Associated Press he is working on expanding its guidelines to Australia, with international music tours in mind.
"Last year, when I first announced this initiative, I thought I was throwing a hand grenade in the room," he said with a laugh. "The entire industry — once they figured out what we were trying to do, they have embraced the project."
Event organizers and managers said they're taking Digby's advice to heart.
"We're going to go back and adapt the trigger plan," said Vilma Salinas, the Country Music Association's senior manager of projects. The CMA Music Festival at Nashville, Tenn., which draws 200,000 fans, has emergency plans in place, but could benefit from more precision on when people need to move, she said.
"The biggest thing is who gets to make the call," she said. "Country music fans are die-hard fans. We need to be as clear as possible."
As tornado expert Chuck Doswell told the conference, severe weather is relatively rare but inevitable.
"Imagine the Indianapolis 500 ... with those hundreds and hundreds of RVs with nowhere to go," Doswell said. If a tornado such as one that killed 158 in Missouri two years struck an event that did not have a severe weather plan in place, "it would make Joplin look like a Saturday afternoon picnic."