The World's Deadliest Tornadoes | Mega Disaster | Spark

Wow! What a tornado! Tornadoes are unpredictable. The whole country looked like it was in a nuclear blast or something. And lethal. I kept talking to myself, thinking, well, this is it. They leave behind obliterated towns. There were no houses left. They were all gone. And bewildered scientists. It's not an exact science. Each tornado is unique. Most dangerous, a few deadly. From the tremendous, to the terrifying, to the tragic. This is a countdown to a mega tornado. One that experts believe will devastate a major American city. The most ominous tornado warning comes when an apocalyptic-like darkness fills the sky. These clouds are precursors to a powerful storm. A supercell. Most tornadoes form when a violently rotating column of air stretches down from that supercell to touch the earth. In general, the faster the wind speeds, the more dangerous the tornado. Surprisingly, relatively little is known about these giant killers. Scientists are literally chasing the mysteries of tornadoes across the great plains of the United States, better known as Tornado Alley. More than 400 tornadoes threaten to wreak a path of destruction here every year. Far more than any other place in the world. The main reason? Ideal atmospheric conditions. The mountains to the west, the Gulf of Mexico to the south, and the fact that there are no physical barriers between here and the North Pole means that we are frequently changing air masses from warm to cold and back again. Tornadoes are measured using the F-scale. F for Dr. Theodore Fujita, who classified tornado strength by estimating wind speed based on devastation. The smallest twisters are F-0s. They can reach 116 kilometers per hour, about the equivalent of a small hurricane. At the other end of the scale are F-5s, whose winds reach speeds of up to 512 kilometers per hour. The tornadoes profiled here rise up the Fujita scale, from an F-2 that rips the roof off a house to an F-5 that lays waste to an entire neighborhood. It's all leading up to a mega-tornado, one that some scientists fear will ravage a primary city. 111 kilometers southwest of Wichita lies the small town of Attica, Kansas. Just over 600 people live here. It's a town you could easily miss. On May 12, 2004, a tornado didn't. On that day, the blue skies over Harper County fill with storm clouds. Shortly after 6 p.m., Dan Smith-Eisler heads into Attica. I did some work for the banker in there, and I told his wife, I said, you know, it's going to storm today. Several thunderstorms form over southern Kansas. One look at these storms tells 30-year veteran meteorologist Chuck Doswell they might be a breeding ground for tornadoes. One of the important ingredients that produces a tornado that we're pretty sure is the wind at low levels has to change direction and speed rapidly with height. We call that vertical wind shear. The vertical wind shear typically spins the air into an invisible cylinder. As the wind speed increases and rises, the tornado intensifies and the core pressure drops. Condensation from the dropping pressure builds down the funnel, creating a visible tornado. That's exactly what's happening in the southern Kansas sky. Harper County Emergency Management Director Mike Lorig gets the first tornado warning at 645. And when they start giving us those warnings, we listen and we say, hey, we need to start warning our public from there. We do not know if this is going to be an F-0 or it's going to turn into the monster. In Kansas, meteorologists carefully follow the thunderstorm as it tracks towards Attica. About 725 in the evening, a F-2 tornado had made it to ground right up here just on this hill. The path of it was right across here. As Lorig watches in astonishment, the tornado tears the roof of a home directly in front of him. This act of violence is just one of many. The angry skies over Kansas are far from finished. We thought, okay, hopefully things are over. We've got emergency crews set up for that. And then the storm just suddenly took a life on its own. Storm chasers tracking the Kansas supercell relay information to meteorologists using mobile Doppler radar. They report the tornado's wind speed, location, and one other startling fact. The storm is producing multiple tornadoes. Storm chaser Yvette Richardson's seen a supercell create more than one tornado before. It can be a very dangerous situation because often people will be looking at the main tornado and feeling that as long as they're far enough away or they're taking cover, that they should be completely safe. Her team and others report seeing 16 tornadoes. They vary significantly in size and power. The biggest is an F-4, roughly 160 kilometers per hour faster and with corresponding wind force about three times larger than an F-2. The F-4 heads straight for Dan and Donna Smith-Heisler's home. I was listening to the radio and the TV and they had it exactly pinpointed. They knew exactly where it was at. Knowing a tornado's path gives potential victims an average of 12 minutes warning, enough time to save their lives. The Smith-Heislers get the warning, but Dan ignores it. Mesmerized by the golf ball-sized hail that often precedes a tornado, he refuses to join his wife down in the basement. That scared me and so I started screaming at him to get down and the dog would not come down. He said, well, sugar won't come. And she was going in the door, out the door, in the door. Dogs are smart, they know. So when I screamed at sugar that she came down, he came down. We started hearing this popping noise. Well, we had a rack of canned goods over there. And those cans were popping from the pressure change. It sounded like popcorn was going off over there. The tornado batters Dan and Donna's home with winds estimated at more than 322 kilometers per hour. And that's when I got hit on the head with cement or something. I can still hear myself groan. All of a sudden you're just going to let go with it. And that's where I was when he said, we're not going to make it. And that woke me up and I said, oh yes, we are too, you know. And you pray really hard. The savage winds rip unrelentingly over the Smith-Heisler's home. When they finally stop, the couple emerge from their basement and into a war zone. And I thought, where's the car? And my next thought was, where's the garage? The twister destroyed the couple's two-story home, five barns, dismantled five cars and killed their dog, Sugar. The terror down there was the worst part. The terror. The Smith-Heislers are lucky to be alive. With estimated wind speeds near 400 kilometers per hour, the F4 tornado easily destroyed their home. But even the earlier F2, with winds estimated at 240 kilometers per hour, was capable of ripping the roof off this home. Complex physics transform air into a lethal force, a concept scientists are laboring to understand. What we are trying to do is simulate the tornado as best as we can. So we're actually comparing the wind which we generate here with the measurements made in the field. And the match is pretty good. Sarkar's tornado simulator is the first of its kind in the world. It uses dry ice to create a visual display of the wind inside a vortex. His machine can produce tornadoes up to 1.2 meters in diameter and 2.4 meters tall. It can reach peak wind speeds of 86 kilometers per hour. When combined with scale models, he's able to replicate damage much larger and faster tornadoes inflict on homes and other structures. Normally a portion of the roof fails and creates a hole in the building which then the flow starts getting inside, which then creates more load on the walls and eventually those walls start failing. Sarkar's experiments conclude that the destructive force of circulating wind in an F3 or stronger tornado is at least three times more powerful than straight-line winds. Since few structures in Tornado Alley are designed to withstand even an F1's winds, this is stark proof that even the weakest tornado is capable of causing damage. The residents of Attica were thankful to have survived the fury of the 16 tornadoes that struck southern Kansas. But when a single F4 twister strikes a small Texas town, its bizarre behavior and surprising power threatens to destroy the entire city. Later, a mega tornado strikes a major American city, something experts say will happen. In 2004, a single Kansas storm produced a swarm of tornadoes that ravaged homes, destroyed property and terrorized hundreds. But the power and damage of that outbreak was far surpassed by the stunning force and unpredictable behavior of a single Texas twister. Pampa, Texas has had its share of luck. The town has prospered since oil was discovered here in 1921. Today, 17,000 residents work the hard soil, farming, ranching and refining oil. But the town's location and the Texas panhandle is also its biggest flaw. This is tornado country. On the afternoon of June 8, 1995, Pampa's luck ran out. Randy Stubblefield is a lifelong resident of Pampa. In his two years as sheriff, he's seen his share of violence. But nothing compares to what he's about to confront. About 4 o'clock in the afternoon, we received a call that there was a large tornado that was building on the south side of the Emerald Highway, just about a mile and a half from where we're standing now. Stubblefield grabs his camcorder and rushes towards the twister. I watched it building on the farmland on the north side of the railroad tracks, and it just started building, getting bigger and bigger. Meteorologist Chuck Doswell is also chasing and filming the Pampa tornado. The evolution of the Pampa tornado with respect to the parent thunderstorm was very unusual in my experience. I've never seen anything quite like it. What Doswell sees is remarkable. The tornado is almost standing still. It's impossible to tell what's going on in there. Then, suddenly, the tornado makes a sharp right turn. This odd behavior stuns Doswell. Tornadoes move in a particular direction because they're tied to the storm that's producing them. And the storm that's producing them moves in a particular direction because it's embedded in a wind field which is pushing it in that direction. But the Pampa tornado isn't moving in the same direction as the storm. After a series of sharp turns, the twister loops almost 270 degrees around Doswell. These erratic and unpredictable movements make this a very dangerous tornado. Let's go. And I am completely mystified as to what was going on with that storm. Then it started traveling north. Get everybody inside because this is one big son of a... And hit an industrial complex. Belinda Waldrop works in that complex with her father. She isn't listening to the news. I learned that there was a tornado outside the building when my dad came to the door of the office I was in and said, Belinda, there's a tornado on the ground west of us. I'm curious. I said, can we look at it? And he said, oh, no, we don't need to look at it. We need to get under some cover. Belinda and her father die for shelter as the twister slams towards them. You could hear the tornado approaching. It was like a gyrating, woof, woof, just a churning that just got gradually more intense and louder. The lights began to flicker as the pressure was building and then the lights went out. Whenever you first start seeing the real debris, the metal, the rooftops and all that, that's when it hit the first series of steel buildings in the industrial complex. And then an explosion. The vacuum just took me up off the floor and slammed me into numerous things and was pulling me backward like a rag doll. You're going to see some vehicles going into the air, transport trailers, truck combination. Now, these units weigh probably 22,000 pounds empty. These were sucked up and in the tornado and were going around and around. Stubblefield and Oswell are among the few to ever film a tornado snatching up three ton trucks. This is a massively powerful twister, one that has Belinda Waldrop trapped in its ferocious grip. When I was in it, everything was dark and I just tried to keep my eyes closed to protect my eyes. I kept talking to myself thinking, well, this is it. And at that time I just had a feeling of helplessness because there's nothing you can do. I mean, there's no way you can stop it, you know, or make it go in other directions or anything like that. And it was just a sick feeling. That dropped me out here into the parking lot and just dropped me on my back and I could see the cloud and the tornado. It looked like a white ghost just going up and taking off. Belinda's encounter with the tornado is over, but Randy's is just beginning. But when I realized that it was going to go into the city of Pampa. Stubblefield jumps back into his car and races down the road directly into the path of the tornado. One of my deputies gets on the air and says, watch out, you're too close. Be careful, you're almost there. You know you're too close when debris starts coming in the car with you. I had my windows down and the trash from the circulation was coming into the car with me. It's going into the city at this time. It was headed right straight for the sheriff's office in the downtown section. Well, I had at that time about 65 prisoners in jail. And, you know, we have a big, strong building, but this big, strong tornado. The twister strikes Pampa, destroying or damaging 200 homes and 50 businesses. Most buildings in the industrial park are ripped off their foundations. Belinda is badly injured and in shock. Of course, I was just stunned and numb. I really couldn't feel anything. I felt like my legs were probably broken. I couldn't get my bearings because there was no building. There were no landmarks that I recognized at all. And I was just taken back. Fearing the worst, Belinda desperately searches for her father. He was draped over a motor. He looked dead, honestly. He was limp and he wasn't moving. I managed to scoot over close to him and started rubbing him. He woke up and turned his head and there was blood. And you could just see this white eyeball. Just a terrified look. And I'll always remember that. Just stark. And he immediately said, help me up, help me up. And I said, I can't help you up. I can't get up either. Emergency workers rush Belinda and her dad to the hospital. Both are in serious condition. Five other residents also suffer injuries. Miraculously, there are no deaths. As the wounded begin their recuperation, experts study Stubblefield and Doswell's remarkable footage. To tumble a two or three ton pickup truck along the ground and then hoist it into the air, this takes incredible wind speed. Probably in excess of 150 miles per hour. Dave Llewellyn researches the strange and complex forces at work inside tornadoes. In a tornado, the wind is not just swirling around. It's actually spiraling strongly inwards. Llewellyn believes that once an object like a vehicle is airborne, it can be slammed to the ground by powerful center downdraft winds, then hurled back skywards by updraft winds. This brutal cycle renders the debris unrecognizable before it's finally spat out as a high-speed missile. Amazing. That was 4,600 pounds burned to the crane. Scott Schiff and his team at Clemson University are studying the damage a tornado-hulled car can do. We're really testing this roof slab here. And this was designed to be a shelter. It's about 10 inches thick of solid concrete with a double mat of steel reinforcement. So it's heavily reinforced. It's really designed to be able to take large debris impacts. 3, 2, 1, drop! After multiple impacts, the slab begins to crumble. So after that last impact, we now have a permanent deformation in the slab. That rebar that's down under that bottom mat there started to yield under the load. And we started to see some more concrete spalling down below there. To counter multiple impacts, Schiff is designing a steel mesh net to catch loose debris. If that works, it will be a huge step forward in tornado protection. We have this terrific F5 tornado. What we're looking for is that we are safe during the event and right after the event. Despite the Pampa tornado's unpredictable movements and incredible power, no lives were taken. 608 kilometers away, another Texas town isn't so fortunate when a massive F5 twister turns tiny bits of dirt and wood into lethal weapons. And later, a mega tornado, one that scientists believe could destroy a major American city. The powerful F4 Pampa tornado tossed trucks, destroyed buildings, and threatened the lives of hundreds. Just one notch up the Fujita scale, an F5 twister turns into a killer. Its weapons, specks of dirt and splinters of wood. Gerald, Texas was founded in 1909. Located 64 kilometers north of Austin, the town never fully recovered from the decline of the cotton industry in the 1920s and 30s. In 1997, a tornado threatened to wipe Gerald off the map. From the beginning, the Gerald tornado smacks of something strange. On May 27th, a supercell forms over central Texas. The Gerald tornado is memorable for a couple of things. One was it formed in conditions that at the time we thought were very unusual. The massive supercell lacks strong vertical wind shear, an essential ingredient in typical tornado formation. Meteorologist Bill Gallas teaches tornado forecasting utilizing a virtual reality tornado simulator. To get a tornado in nature, you need to have really two things. You need a very strong updraft, or updraft and downdraft, to help stretch the air in the vertical. And you also need to have some source of spin present. Strong wind shear usually provides a tornado with its source of spin. Before Gerald, the conventional wisdom was that without strong wind shear, you don't get violent tornadoes. But the unusual atmospheric conditions over central Texas are about to prove the conventional wisdom wrong. Dead wrong. Here, the warm, moist air rises so forcefully, it generates a super strong updraft, creating a very powerful and dangerous tornado. As the skies blacken and the winds rage, LaDonna Peterson and her 8-year-old son leave their mobile home for the safety of her mother-in-law's brick house. I went outside and started watching the clouds outside because they were getting real thick, real dark, real heavy. And all of a sudden, I could hear in the distance, because the wind had picked up, the alarm going off in town. Ken Adams doesn't hear the town alarm. He's asleep. And the dog woke me up. And I could tell that dog was really scared. I knew something was wrong, but I don't hear well, but I could feel it. It was like a thunder that you couldn't hear, you know, but you could feel it. LaDonna's sister-in-law and young daughter join her and their mother-in-law's home. News reports place a tornado 3 kilometers away. My sister-in-law and I went to a window, and we could actually see the tornado in the distance, but it was like it was just sitting there, just turning, not moving at all. In fact, the tornado isn't standing still. Its forward movement is clocked at a slow pace of 16 kilometers per hour. But its internal wind speeds are reaching more than 420 kilometers per hour. Now a killer F5, it descends on the women's refuge. Then all of a sudden, we felt a gust of wind hit the house. We could actually see the asphalt being pulled up off the street, up the road from us. We were sitting there, and I said, God, please don't take my family. Then we felt a big gust of wind hit the house, and the bathroom door flew open. And at that point, we just started feeling like mud and stuff start coming in, hay. Minutes later, when Ken Adams walks outside to see why his dog is barking, he comes face to face with a nightmare. It was so big at the base, probably a half a mile or three quarters of a mile, that I didn't realize it was a tornado. And by the time that I did realize it, it was too late to go anywhere. I ran to the house, opened the back door, and as I did, the door flew out of my hands, and the roof of the house came off. I would sort of be picked up, the house would fall on me again. Suddenly, the tornado is gone. The whole country looked like it was in a nuclear blast of some type. When I first looked up, I thought I was dead. I mean, I really did. Ken is wrenched back to reality when he's forced to take in the horror that surrounds him. More than 300 head of cattle were killed or injured by the tornado. Many that survived had to be shot because of the extent of their injuries. Oh, it was terrible. There's about 300 acres over there, and most of it, you couldn't walk very far without smelling that old dead smell. LaDonna's family emerges from the rubble of their home and into a wasteland. Nearly every home in their subdivision is obliterated. Many of their neighbors are nowhere to be seen. Others are badly injured. Mrs. LaFrance was pinned under a tree, and her daughter was laying in the mud and had some really severe injuries to her legs and her arms. It was raining, and she was saying it was hurting her, hitting the open wounds, so the only thing I could find was a dirty blanket laying on the ground to cover her up with, just to keep the rain from hitting the wounds so bad. Later, we found out that Mr. LaFrance had been killed in the tornado, and the daughter had been crying through the whole thing, wanting to know where her dad was. Twenty-seven people died that day. Half were children. Entire families killed. As scientists studied the Jarrell tornado, several intriguing facts came to light. The thing that the tornado itself was interesting for was that it was moving very, very slowly, and it was large, and it collected a lot of debris, to where the high wind speeds associated with the tornado were there for minutes in locations, rather than just for a few seconds. The tornado traveled approximately 16 kilometers per hour, significantly slower than the average 48-kilometer-per-hour twister. Another oddity was that most houses in the tornado's path were completely obliterated. After much study, experts found an answer. Physicist Dave Llewellyn's computer models illustrate their findings. You can actually have thousands of tons of dirt in that debris cloud at any given time, and that dirt can change the internal structure of the tornado. As the Jarrell tornado passed over the open Texas plain, it picked up massive amounts of dirt, slowing down the funnel's forward movement while increasing its destructive power. I think down low that Jarrell tornado probably acted like a giant sandblaster. Llewellyn and others believe that instead of blowing apart homes with strong winds like some tornadoes, the Jarrell twister destroyed structures via the massive force of windblown debris. The Jarrell tornado was as ironic as it was tragic. Experts advise never to try and outrun a twister, but some who died in Jarrell could have escaped the slow-moving storm in cars. Experts advise potential victims without storm shelters to hide in interior rooms like closets or bathrooms, but some in Jarrell did exactly that and died anyway when their entire home was swept away. Still, because no two twisters are ever the same, experts advise that the best option is an underground shelter or safe room built to specific codes. The Jarrell tornado changed the way experts watch for twisters. They now view storm systems with low vertical wind shear as possible violent tornado producers. But no amount of vigilance or insight could stop the deadliest tornado in U.S. history from killing hundreds. And later, a megatornado unseen in modern times threatens millions. The Jarrell twister killed 27 people while changing the way experts keep vigil for potential tornado-producing storms. But there was no way to prepare for the deadliest tornado in U.S. history, a brutal F5 that tore through three states, killing hundreds. On March 18, 1925, a single tornado slaughtered 695 people in Missouri, Illinois, and Indiana. The behemoth F5 blasted a 322-kilometer path of unstoppable annihilation that lasted for hours. Survivor accounts are chilling. The air was filled with 10,000 things. Boards, poles, whole sides of little framed houses. In some cases, the houses themselves were picked up and smashed to the earth. And living beings, too. A baby was blown from its mother's arms. Children all around me were cut and bleeding. They cried and screamed. It was something awful. The destruction was of mythic proportions, primarily because the killer struck an extremely vulnerable population. People had very few ideas about how to deal with tornadoes. The country was largely rural instead of mostly metropolitan. And they had essentially no way to communicate with each other. The town of Murfreesboro, where more than 100 people were killed, actually was hit more than two hours after the first fatalities from the tornado. And people wondered why hadn't any word gotten downstream, down the telephone lines or telegraph lines, that something was coming. In 1925, several million people lived in small rural towns throughout Tornado Alley. Today, tens of millions call it home. Modern communication means better warnings, but evacuating a major city before an F5 strikes is still impossible. On May 3rd, 1999, the people of Oklahoma City faced the worst F5 in modern history. The T9 tornado that went through Moore in southern Oklahoma City was one of the most damaging in the history of the United States, no matter how we look at the data. Late in the afternoon of May 3rd, 1999, weather forecasters in Oklahoma carefully track multiple supercell storms and then the tornado reports that begin flooding in. At home with her eight-year-old son, Dana Grimm watches the local news. We had been watching the coverage for hours. He said it just kept building momentum, getting bigger and bigger, and if you were above ground, you weren't going to make it. The storm system is intense, complicated, and growing. Weather trackers watch in awe and shock as multiple storms produce multiple tornadoes. It seemed like just about every thunderstorm cloud that formed eventually produced a tornado at some point. And there were times when you had the main tornado happening, and then we had what we call satellite tornadoes that would rotate around it. They're completely separate tornadoes within the same storm system. At about 6.25 p.m., a large tornado touches down just outside Amber, Oklahoma. Doppler radar records its wind speed at 512 kilometers per hour, the fastest twister ever documented. This is a monster, and it's hurtling towards Dana Grimm's home. And they had said that it was a mile wide and just ferocious, and it was just destroying everything in its path. When just 1.6 kilometers away, Dana and her son hide in a closet. I remember my son, he was screaming and crying. He said, are we going to be okay? I said, we're going to be fine. He said, what do we do? And I said, we pray. Dana's fear turns to panic when she hears the tornado strike. There was kind of a high-pitched squeal to it. And then, of course, the sound of everything, the windows just blowing out. The house was shaking. We could hear the beams in the roof breaking. The walls just lifted up, and we could feel really cold air rushing underneath. And within seconds of that, the house just blew up. I couldn't breathe. I had sucked in so much dirt that I couldn't even breathe anymore. I thought, this is it. And I remember just praying that, God, if this is it, I'm ready. On the brink of death, the fierce tornado spares Dana's life by lifting her out of the suffocating dirt. When it slams her back to the ground, she's paralyzed with fear. And I realized then that I didn't have my son. So I started screaming for him, and he came running over, and it was really, it was just a miracle of God, because we were both barefoot. He came running over to me, did not have one puncture wound on his feet. The F-5 continues towards the center of Oklahoma City, crossing major highways filled with rush hour traffic. As the tornado hurtles towards them, some people panic. They abandon their cars in a desperate attempt to find shelter. For a few, that decision has fatal consequences. Three people seeking refuge under freeway overpasses are killed by debris and the sheer force of the wind. Stranded cars block escape routes for many others. Shields Boulevard in Oklahoma City essentially became a huge parking lot, and it blocked people from being able to escape the tornado. By the time the F-5 dissipates, 40 people are dead and nearly 700 injured. My wife worked in the hospital in Norman that night, and she worked in the emergency room, and they were swamped, of course. She saw some really horrific injuries. People came in covered with splinters of wood that looked like pin cushions. So much wood. Awful things. Many survivors suffer multiple painful wounds from being impaled by debris. Cheryl Brown studied the injuries and deaths in Oklahoma. There were also injuries that were related to debris being embedded inside the body, all the way from small splinters to very large objects such as 2x4s. Many survivors suffered debris-related injuries because the tornado destroyed so many homes, spewing countless shards of wood and other material into the air. The Oklahoma twister leveled nearly 3,000 houses and structures. Three, two, one, fire! 73 miles an hour. Schiff and his team at Clemson University fire 2x4s at more than 160 kilometers per hour into a variety of structures to represent the damage done during a tornado. I think that the public understands that tornadoes are very dangerous. What they don't understand is that in typical construction, they have very little protection against those types of events. When debris strikes a home, it does far more damage than simply making a hole in a wall or window. Fire! It gives the tornado a point of entry. Once inside, in-flowing air can rip apart walls and tear off the roof. The home then becomes part of the tornado's arsenal, further fueling the funnel with debris and making it even more destructive. This type of construction is very typical for a residential brick veneer in front of a wood frame wall. Fire! The missile's gone all the way through the wall cavity. Most people that have this type of house would be vulnerable to an F5 tornado. Fire! Schiff's experiments determined that for a home to withstand the deadly onslaught of debris, the brick veneer must have an 8 centimeter thick backing of concrete. So this wall here would be suitable for a shelter to resist tornadoes. Most homes in Oklahoma City were brick veneer with wood frames. This common construction, coupled with the sheer number of homes in the tornado's path, increased the debris field exponentially. Dana Grimm survived with a broken back, her son with a puncture wound to his chest. I truly believe that the reason that I was thrown twice, if I had not been picked back up and thrown again, I would have suffocated because I could not breathe in anymore. Ten supercell storms spawned 70 tornadoes that spring day, including the F5 that cut a 24 kilometer path over interstate highways and devastated several suburbs of Oklahoma City. It was sad. I think there were 14 in our own housing addition that died. And it's a miracle of God that we didn't. The Oklahoma tornado caused more than a billion dollars in damage, the costliest tornado in U.S. history. Complete and total devastation. The homes that you see over here now were completely gone. It was a rubble pile. If you had been in the open, it would not have been a very pleasant place to be. Things would have been much worse if the tornado had veered just 16 kilometers to the west, striking the heart of downtown Oklahoma City. Even so, the Boer, Oklahoma tornado and its companion twisters rank as the most deadly and destructive outbreak in modern history. They would be far surpassed by an F5 striking a major American city. That would be a mega disaster. One experts warn could happen. Every year, major U.S. cities in Tornado Alley play a game of Russian roulette with massive twisters that wreak havoc there. In 1999, Oklahoma City lost the game when a giant tornado killed 40 people, injured nearly 700, and racked up costs of more than a billion dollars. Only sheer luck kept the tornado from striking downtown. Researcher Scott Ray knows the next major city to be struck by an F5 may not be so fortunate. Dallas is overdue for a large violent class tornado. Dallas, Texas is a boomtown sprawled along the southern boundary of Tornado Alley. It's one of the largest and fastest growing metro areas in the U.S. with more than 5 million residents and 600 corporate headquarters. Dallas is 10 times larger than Oklahoma City. I was shocked a bit when I saw some of the aerial footage of Oklahoma City. The amount of damage that had occurred in that was pretty amazing. Ray assists local governments with planning for hazards, especially threats from tornadoes. To help Dallas prepare for a possible mega disaster, he has modeled over 60 different scenarios of how the Dallas region would be affected by a violent tornado. For reasons of credibility, it was very important that we look at an event that actually had occurred somewhere else. So we took the event at Oklahoma City basically because the data was very good for that particular event. And we could transpose it by just moving those same geographical characteristics of the tornado on top of the geography of Dallas-Fort Worth. So we got to see it kind of from our own perspective. Ray and his team painstakingly overlaid the exact path taken by the Oklahoma tornadoes over the Dallas-Fort Worth area. A mega disaster unfolds when Oklahoma's F5 tornado rampages through downtown Dallas. It would easily be the worst damaging tornado event that we have had to date in the U.S. Ray's nightmare scenario begins as a supercell storm forms over north-central Texas. A 160-kilometer-per-hour tornado, an F3, touches down in a dusty field 10 miles southwest of Dallas. Its first target is the suburb of Cockrell Hill. With packing winds in excess of 320 kilometers per hour, cars are tossed aside, buildings are decimated. The tornado continues northeast, unrelenting in its assault on thousands of homes. But Twister's internal wind speeds rise past 400 kilometers per hour, turning it into an F5. Fueled by tons of debris, the giant tornado slows as it descends on the busy freeway. A clogged highway holds a heck of a lot more people than one that is moving comfortably. And the other problem that you have is, where do you go? Panic ensues as many abandon their cars, creating a traffic jam that traps thousands. The 443-kilometer-per-hour winds effortlessly swat cars off the highway. Anyone hiding under an overpass is vulnerable to flying debris and violent winds. Cars snatched up by the powerful updraft winds are spun around inside the giant vortex, then shot out, creating a dangerous hazard for anyone in their path. Next, the deadly Twister approaches downtown Dallas. Dozens of skyscrapers and tens of thousands of people crowd the city. Giant glass windows shatter. Marble and bricks are ripped off buildings. A deadly shower of glass and other debris rains down onto the crowd below. Most of the skyscrapers in the Dallas-Fort Worth area are predominantly covered with glass on the outside, and that's not very durable. But the amount of damage from getting wind and broken glass spread out through a downtown area is going to be pretty dramatic. A packed commuter train snakes through the city. It's swept off the tracks and slammed into a skyscraper, killing hundreds in the train and office buildings. There's little doubt that debris would be probably the largest generator of damage in the metroplex. And it's basically because there's so much of it that can be generated. And you name it, it could be wood, bricks, gravel, just about anything you can imagine can become a projectile. And with almost unlimited supply. The tornado continues north, leaving the wreckage of downtown Dallas behind. Tornadic winds more than 500 kilometers per hour now descend on the suburban landscape of Lakewood. 92,000 people living here have had up to 20 minutes to seek underground shelter, a seemingly reasonable chance for survival. But like the Gerald, Texas twister, those hiding in closets or bathrooms can only pray. Finally, the worst tornado in history slowly drifts skyward and dissipates. The war zone behind it is 61 kilometers long. Dallas is devastated. I don't think there's any way to really sugarcoat an event. It's going to be difficult to deal with regardless. So there's going to be a lot of damage. There are going to be a lot of people that need help. Total damages approach $5 billion. Tens of thousands are homeless and scores injured. The death toll is unknown. Fatalities are difficult to really quantitize because they involve people making decisions. And there are good decisions that can be made, bad decisions. We don't know what decision they're going to make. The best decision city planners can make is to prepare with multiple underground shelters, rehearse evacuation plans and a vigilant public. But even that won't likely be enough. I think it would pretty much be impossible financially to build a city that could really survive violent class tornadoes or any scenario like that. With increasing populations in major metropolitan cities throughout Tornado Alley, science is in a life or death race against time to understand one of Mother Nature's biggest secrets. In an ideal world, we'd have radar or other instrument measurements on every tornado that occurs. In the practical world that we live in, that's just not going to happen. Okay, this storm in the next hour is going to produce this type of tornado. We're just not there yet and it's hard to say when we'll be there. We've certainly got a ways to go. Given the limited ability to predict tornadoes, there is a very real cause for concern. Most people think about disasters as very random events that can happen to them. And I think that holds true with tornadoes as well. If you wait long enough, something resembling the worst case scenario is going to happen eventually. Until science learns more about these brutal forces of nature, the only thing that can be done is to prepare before a mega-disaster strikes.