Missouri and Illinois have averaged five tornadoes each per month for the past two decades, based on data from the National Oceanic and Atmospheric Administration.
Some, like the tornado that tore through the small community of Defiance in St. Charles County last Friday, have caused deaths and leveled buildings. The same storm system spawned another tornado that evening, which crushed portions of an Amazon warehouse in Edwardsville, Illinois, killing six workers.
Despite the frequency of tornadoes in Missouri and Illinois, the two states have few regulations directly related to tornado safety — instead relying on a patchwork of city- and county-adopted building codes. Now, some elected officials are questioning whether current requirements are sufficient to protect residents from powerful storms.
In 2014, Illinois legislators approved a measure requiring that all new school buildings include storm shelters. The legislation does not apply to other buildings, such as commercial warehouses or businesses.
At a press conference Monday in Pontoon Beach, Illinois Gov. J.B. Pritzker said he is considering whether the state should update its building codes in response to more frequent, severe storms.
“It makes me wonder whether or not we need to change code based upon the climate change we’re seeing all around us,” he said. “While we cannot prevent natural disasters, we can strive to prevent future tragedies and ensure that all Illinoisans make it home safe at the end of their shift.”
Though it’s difficult to connect any single storm to climate change, scientists warn that warming atmospheric conditions can fuel severe thunderstorms and tornadoes.
Tornadoes are often linked to powerful “supercell” thunderstorms, said Jim Sieveking, a meteorologist with the National Weather Service in St. Louis. The thunderstorms develop when warm, moist air surges up from the Gulf of Mexico and rises into a band of cooler air, creating a rapid change in wind speed or direction known as wind shear.
“St. Louis has a history of seeing strong and violent tornadoes during the wintertime,” Sieveking said. “We’ve had events as far back as 1959, but now, we’ve had 2010, 2013 and 2021. Perhaps the frequency of these events are increasing, and that could be attributed to the warmer conditions.”
Between 1950 and August 2021, the National Oceanic and Atmospheric Administration recorded 2,956 tornado events in Illinois and 2,765 in Missouri — just over three tornadoes per month in each state, on average. Since 2001, that average has inched up to about five per month for each state.
Though tornadoes have become more frequent in recent decades, the increase is likely linked to advances in the technology used to detect them, including Doppler radar.
Sieveking recently visited Defiance with a team of meteorologists to assess the strength of last week’s tornado, based on the damage it carved along a 21-mile path.
“It was a very, very intense tornado with a very narrow path of destruction, maybe 100 yards wide,” he said. “The first house it hit was completely destroyed. That house was not really anchored down to anything; even some of the foundation cracked from the tornado.”
The National Weather Service of St. Louis rated the tornado that touched down in Defiance as an EF-3, with wind speeds reaching 165 miles per hour. At least two people were injured and one died.
In Missouri, there are no statewide building codes, said Assistant State Fire Marshal Matt Luetkemeyer. “Each county, municipality, etc., is responsible for establishing whatever code they see fit for their community,” he said in an email.
There are also no statewide requirements for storm shelters, said a spokesperson for the Missouri State Emergency Management Agency.
Some municipalities have instituted local ordinances related to tornado safety, including Hawk Point in Lincoln County, which requires below-ground storm shelters for mobile home parks.
Compared to hurricanes and other severe weather, tornadoes can appear with relatively little warning, said Marc Levitan, an engineer with the National Institute of Standards and Technology. Without the luxury of time to prepare, protective measures need to be able to be deployed quickly.
“You wouldn’t use a system where you’d have to get out on a ladder and bolt shutters on like you might have to do in a hurricane-prone region,” Levitan said. “You’d need something that’s permanently affixed or impact-resistant.”
After a tornado killed 161 people in Joplin in 2011, Levitan and other federal researchers at NIST launched a technical investigation to understand why the storm was so destructive — and to develop standards for buildings that could withstand future tornadoes.
“Our keystone recommendation was if we’re going to reduce the impacts of tornadoes, we need to start designing for tornadoes,” he said.
Based on the investigation, NIST recommended building code changes for the nation’s most tornado-prone regions, as well as storm shelters capable of withstanding 250-mph winds.
But the agency stopped short of recommending a one-size-fits-all approach for shelters, instead suggesting communities use the national guidelines “to develop the safest, most efficient and most economical sheltering strategy possible based upon the needs of the community.”
NIST is a non-regulatory federal agency, which means it does not have the authority to implement tornado-related regulations. But Levitan hopes state and local governments will adopt the recommendations, so communities can be better prepared for the next tornado.
Tornadoes can be very destructive, he said, “but there is something that we can do about them.”
Brent Jones contributed to this report.
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