In 2004, the Indianapolis 500 turned into the Indianapolis 450. Organizers shortened the famous automobile race by 20 laps (50 miles) after a tornado touched down near the Indianapolis Motor Speedway, where more than 200,000 spectators were in attendance. Large outdoor gatherings such as this expose event-goers to the elements, and in some parts of the United States, severe weather can make that pairing deadly.
That’s especially true of the New Orleans Jazz & Heritage Festival in Louisiana, which poses the highest lightning risk of more than 16,000 large outdoor gatherings analyzed by researchers in a recent study. Coors Field in Denver and an amusement park in Arlington, Texas, topped the study’s lists for tornado exposure. The findings increase awareness of weather-related hazards among event attendees and venue managers alike, the researchers suggested.
Only a handful of studies have attempted to quantify weather-related risks at large outdoor gatherings, and even fewer have attempted to do so for a variety of events that occur across a large geographic area.
Stephen Strader, a hazards geographer and atmospheric scientist at Villanova University in Pennsylvania, and Jack Deppman, a doctoral student in geospatial analytics at North Carolina State University in Raleigh, recently did just that. Strader and Deppman focused on two forms of extreme weather—tornadoes and lightning—and determined risk indices for large outdoor gatherings across the United States.
The researchers started by mining tornado and lightning data. They analyzed a NOAA dataset of tornadoes that touched down between 1954 and 2020 and a dataset of cloud-to-ground lightning strokes pinpointed by the Earth Networks’ Total Lightning Network from 2012 to 2020. For each type of hazard, the researchers calculated the average number of occurrences each month within grid cells measuring 80 × 80 kilometers.
Follow the Crowds
Strader and Deppman next assembled a list of large outdoor gathering spaces. The public venues tabulated in the Department of Homeland Security’s Homeland Infrastructure Foundation-Level Data dataset served as a basis, and the researchers supplemented that listing with other locations such as football stadiums, concert venues, and horse racetracks.
For each location, Strader and Deppman determined the dates of events that occurred primarily outdoors and each event’s maximum seating capacity. To do that, they mined sources ranging from reports to venue websites to news articles. Amassing all that information took about a year.
After limiting their final list of events to those that could accommodate at least 10,000 people, the researchers identified 16,232 unique events held at 477 venues. “It’s a lot of data,” said Deppman.
Next, the team determined risk indices for each event. Strader and Deppman’s calculations took into account an event’s maximum seating capacity, its frequency in terms of number of days per month, its seasonality, and the tornado and lightning climatology of its location. “We needed to capture all of those elements,” Strader said.
Strader and Deppman calculated one lightning risk index and two tornado risk indices for each event. It was important to consider the risk of experiencing any tornado, independent of magnitude, and also the risk of experiencing a more damaging tornado, Strader said. That’s because though more than four out of five tornadoes are classified as EF0 or EF1 on the Enhanced Fujita damage intensity scale, the vast majority of tornado-related fatalities occur during tornadoes rated EF2 or higher. “They’re responsible for 99% of deaths,” Strader said.
Music, Baseball, Roller Coasters, and More
When the researchers ranked the events, they found that the New Orleans Jazz & Heritage Festival topped the list for potential lightning exposure. “That stuck out like a sore thumb from the lightning standpoint,” Strader said. This event, which draws roughly half a million attendees annually over a week and a half, occurs in April–May, which is when the risk of cloud-to-ground lightning peaks in southern Louisiana. All of the other events in the top 10 for lightning exposure were at amusement parks in Florida.
“Amusement parks dominate the scores because they’re open so many days per year.”
Coors Field in Denver in June topped the list for exposure to EF0–EF5 tornadoes. Other venues on the top 10 list included the New Orleans Jazz & Heritage Festival; several amusement parks in Texas, Florida, and Missouri; and the State Fair of Texas in Dallas.
When the team limited their analyses to more damaging tornadoes registering EF2–EF5, the Six Flags Over Texas amusement park in April was ranked first. Other amusement parks in Ohio, Florida, and Texas joined the top 10 list, as did Globe Life Field, a Major League Baseball stadium in Texas; the State Fair of Texas in Dallas; the Texas Grand Prix; and the Indianapolis Motor Speedway.
“Amusement parks dominate the scores because they’re open so many days per year,” Strader said. The team’s results were published in Weather, Climate, and Society, and the full ranking of events is available upon request from the authors.
It’s important for the operators of venues to look at these results, said John Jensenius, a meteorologist and lightning safety specialist and a member of the National Lightning Safety Council, who was not involved in the research. But event attendees also have responsibility for their own safety, he added. With weather apps widely available, people can make educated choices about whether to attend a particular event. “Avoidance is always the best answer if you think there’s going to be lightning at an event,” Jensenius said.
“Venues need to be, and generally are becoming, better prepared for these types of events.”
Some venue managers and event organizers are already taking weather-related risks seriously. Last year, a football game between Penn State and West Virginia universities was interrupted by lightning, and officials opted to evacuate Mountaineer Field at Milan Puskar Stadium, an outdoor space capable of holding roughly 60,000 fans. “Venues need to be, and generally are becoming, better prepared for these types of events,” said Roger Edwards, who retired last year as a meteorologist and lead forecaster at NOAA’s Storm Prediction Center in Norman, Okla. Edwards was not involved in the research.
Strader is now thinking of ways to expand the team’s database. There’s plenty of other forms of extreme weather that could wreak havoc on a large outdoor gathering, he said. “What about wind, hail, flash flooding?”
—Katherine Kornei (@KatherineKornei), Science Writer
Citation: Kornei, K. (2025), Large outdoor gatherings expose event-goers to severe weather,
Eos, 106, https://doi.org/10.1029/2025EO250152. Published on 21 April 2025.
Text © 2025. The authors.
CC BY-NC-ND 3.0Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
