- 05/23/2013 by Stephanie Pappas (LiveScience)
The scenes of devastation in Moore, Okla., after a possibly 2-mile-wide tornado tore apart schools and homes on Monday (May 20) led to an inevitable question: Could anything have been done to save buildings and lives?
The answer, according to tornado experts and building engineers, is yes — though there are roadblocks in the way. Some are scientific, because meteorologists have yet to fully grasp why tornadoes form when they form and how to predict their paths. Others are economic: Building a tornado-proof building, for example, is already completely possible, albeit very expensive.
"There's no doubt we could engineer something that could withstand [an EF4 or EF5 tornado]," said Darryl James, a professor of mechanical engineering at Texas Tech University. "The question is, who could afford it?"
Despite these challenges, researchers are working to make sure future tornadoes wreak less destruction, whether that means getting a better grip on where tornadoes are likely to form and move or protecting property and people once the tornadoes have arrived.
The Moore, Okla., tornado touched down at 2:56 p.m. CDT (3:56 p.m. EDT) on May 20 and spent 40 minutes on the ground, carving a 17-mile-long (27 kilometers) path of destruction through the Oklahoma City suburb. The National Weather Service pegged the tornado as an EF5 on the Enhanced Fujita scale, meaning winds reached more than 200 mph (322 km/h). [See images of the Moore tornado damage]
Tornados as strong as the one that ravaged Moore are relatively rare. About 95 percent of tornadoes in the United States are EF2s or below, according to the National Climatic Data Center. Only about 1 percent reach EF5 status. Predicting which storms will generate monster tornadoes — or any tornadoes at all — remains a challenge.
The basics of tornado formation are simple enough. When wind and humidity conditions are right, thunderstorm systems can begin to rotate and become what are called supercells. Supercells are marked by the presence of a mesocyclone, a rotating updraft of air that can sometimes create a funnel cloud. Exactly why this happens in some storms and not others is a key mystery.
"We're trying to be able to figure out why of two pretty much identical supercells, one will generate a tornado and one won't," said Amy McGovern, a computer scientist at the University of Oklahoma in Norman.
McGovern and her colleagues are among the researchers trying to improve tornado predictions. Using supercomputer simulations, she and her team are working to model tornadoes on a very fine scale, tracking their movements to within 165 to 245 feet (50 to 75 meters).
On-the-ground observations can only take researchers so far, McGovern said. Radar can't sense every component of the wind's movement, for example. By using simulations, she and her colleagues want to set up at least 100 storms they can tweak at will, altering one variable such as humidity or temperature to see whether and how each influences tornado formation.
At the 165- to 245-foot level of precision, building a stable, realistic simulation is difficult. So far, McGovern and her team have created about 10 storms, she said, far fewer than the 100 they need. But she is hopeful. The team has done similar work to predict airplane turbulence with great success, so once the database of simulated storms is built, using them to predict real-world weather should be successful, she said.
Better prediction gives people more time to seek shelter when a tornado is bearing down. On Monday, the National Weather Service office in Norman, Okla., gave residents 16 minutes of warning before the tornado even formed, based on radar indicators that the storm clouds were circulating in such a way that a tornado was likely. That 16 minutes is 3 more minutes than the average tornado warning time of 13 minutes. (The actual time most residents had to seek shelter was been longer, because it took the tornado time to reach them.)
Ultimately, researchers want to get quicker. McGovern's work could help meteorologists look for clues in storms that make tornado conditions more likely. The eventual goal, said William Gallus, a meteorologist at Iowa State University, is "warn-on-forecast." In other words, meteorologists would be able to forecast tornadoes and issue warnings, rather than waiting to see rotation or a funnel cloud in the sky.
"We believe our computer weather prediction models might be getting good enough that we might be able to give people somewhat more warning, maybe an hour or half-hour of advanced warning," Gallus told LiveScience.
Using tornado simulators, Gallus and his colleagues are working on understanding how local topography affects the way a tornado might move and strengthen. For example, they've found that ridges cause tornadoes to deviate left as they climb up and right as they descend. Narrow valleys can also funnel wind into tornadoes from a mile or so away, Gallus said, causing damage far afield from the actual funnel cloud. [50 Amazing Tornado Facts]
Moore, in particular, has been hit by three violent tornadoes in less than 15 years: One in 1999, one in 2003 and one on Monday. Most scientists see that as a coincidence, but Gallus believes it's worth looking into the local landscape for possible influencing factors.
"Statistically, that should not happen for about a million years, to have a violent tornado pass by the same spot three times, because they are just so rare," he said, adding, "It's possible there are some things present that might help influence the track or how strong they get."
Gallus isn't the only researcher looking to get a hyper-local look at how tornadoes work. Colorado State University engineer V. Chandrasekar and his team are working to deploy small networks of radar in urban areas. The system, tested in Oklahoma and now being moved to Dallas-Fort Worth, Texas, allows researchers to get full three-dimensional information about how wind is moving. (Traditional radar provides only one component of wind movement.)
"What we are about is getting higher resolution in space and time," Chandrasekar told LiveScience. "For example, today's technology takes about 5 minutes to get an update … we can provide updates every 30 seconds to a minute."
Once a tornado is on its way, though, saving lives can be a matter of having a place to go.
In Moore, students at Plaza Towers Elementary huddled in interior hallways and bathrooms, but a direct hit by the tornado collapsed most of the building. Likewise, homes in neighborhoods hit by the tornado were completely destroyed. As of Wednesday, the death toll stood at 24, 10 of whom were children. [Video: Moore, Okla., "War Zone"]
Sad experience is teaching that some old tornado safety tricks aren't as effective as hoped — particularly when buildings aren't designed with tornado safety in mind. In Joplin, Miss., a 2011 tornado killed 158, according to the National Weather Service (the city of Joplin pegs the death toll at 161). Among the devastated buildings was a local high school, and some of the spots disaster experts would normally suggest people go for shelter turned out to be among the most badly damaged there.
Interior hallways are usually the suggested shelter spots, but in Joplin, doors and glass windows at either end of long halls were destroyed by debris, creating a dangerous situation, Gallus said.
"Hallways became wind tunnels," he said. Architects like natural light, he said, but "probably when we design schools in the future, we need to be careful how we design them."
Building in tornado country
Even in Tornado Alley, buildings are designed to withstand only 90 mph (145 km/h) straight-line winds, said Partha Sarkar, who studies wind engineering and aerodynamics at Iowa State University. The standard is based on historic measurements of thunderstorm winds and doesn't take into account even the most common types of tornadoes. An EF1 tornado can sustain gusts of up to 110 mph (177 km/h).
What's more, Sarkar said, rotational tornado winds can put even stronger stresses on buildings than straight-line winds. A 90-mph tornado can be much more damaging than a 90-mph straight gust.
"The buildings are simply not designed to withstand that level of wind," he told LiveScience. [The Deadliest Tornadoes in U.S. History]
Designing a tornado-proof building is expensive, Sarkar said. You need reinforced masonry, steel or composite materials instead of timber, and enhanced connections between walls, foundations and roofs.
"I personally believe that we can do some incremental improvements and that will certainly help to make them stand up to most medium-intensity tornadoes, EF2s, EF3s, maybe," Sarkar said. "But when it comes to EF4 and EF5, certainly the cost is going to be prohibitive."
Schools, hospitals and high-density buildings like shopping malls could be designed to these higher standards, Sarkar said. Another option would be tornado shelters — another feature frequently missing from Tornado Alley construction.
"The storm shelters today are designed for 250 mph (402 km/h) wind speeds, and we feel that is higher than will ever be experienced at the ground level in a tornado," said Ernst Kiesling, a mechanical engineer at Texas Tech and the executive director of the National Storm Shelter Association.
Shelter from the storm
Unfortunately, cost prevents homeowners in even tornado-prone areas from installing these shelters. In Oklahoma, Kiesling said, perhaps one in every five newer homes has an in-home shelter or safe room, a reinforced room that can be used on a day-to-day basis as a bathroom or storage closet. The number is lower in older homes.
A small in-home safe room added to a new house raises the cost of construction by about $5,000 to $6,000, Kiesling said. Retrofitting an old home would be more expensive. And, of course, some homes can't be retrofitted — mobile homes, for example, have no slab to fasten a shelter to. In-ground shelters can be equally as elusive in mobile home parks.
"The landowner is typically not the homeowner, so who is going to make the investment to make a shelter in the mobile home park?" Kiesling said.
The Federal Emergency Management Agency provides funds in some areas to offset the cost of constructing safe rooms. Education about the need for safe rooms can also make a difference, Kiesling said.
For Sarkar, tornado-ready construction is a national issue.
"It's not going to go away," he said. "And if we don't change the current mindset and building codes that are followed, sadly, things are not going to improve."
The tornado that ripped through Moore, Okla., on May 20, 2013, flattened homes and piled cars on top of one another.
CREDIT: 1984 Studios, Flickr