On May 20, 2013, a ferocious EF5 tornado over a mile wide tore through Moore, Oklahoma, inflicting 24 deaths and obliterating entire neighborhoods. It was the third time an exceptionally violent tornado had struck the city in 14 years. Yet predicting when and where these killer storms will hit still poses a huge challenge. Why was 2011—the worst ever recorded tornado season that left 158 dead in Joplin, Missouri—followed by the quietest ever year of activity prior to the Moore disaster? Can improved radar and warning technology explain why so many fewer died in Moore than in Joplin? And will tornadoes get worse as Earth's climate heats up? In this NOVA special, we meet scientists in the front ranks of the battle to understand these extreme weather events. We also meet storm survivors whose lives have been upended and learn how we can protect ourselves and our communities for the uncertain future. (Premiered May 29, 2013)
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Oklahoma's Deadliest Tornadoes
PBS Airdate: May 29, 2013
NARRATOR: One of the worst tornadoes in decades rips homes, schools and families apart.
MAYLENE SORRELS (Moore Tornado Survivor): It's blowing and sucking the air out of the room.
NARRATOR: In May, 2013, an EF-5, the most severe category of tornado, strikes Moore, Oklahoma. The 200-mile-an-hour winds slammed into a school, killing seven children. Up to then, spring, 2013, had been a quiet season. But just two years earlier, 2011 was the fourth deadliest tornado season on record.
Over a hundred and fifty die in one city alone: Joplin Missouri.
STORM CHASER: Houses are gone. It's massive.
NARRATOR: What can be done to prevent such disasters in the future.
ADAM WRIGHT (Joplin Tornado Survivor): We have to figure out a better warning system.
NARRATOR: But a better warning system requires a better understanding of tornadoes.
HOWARD BLUESTEIN (University of Oklahoma): There's an urgency to try to crack the code, so we have to keep going and get data as often as we can.
NARRATOR: And all that data could lead to better prediction and save lives.
STACEY BARTOW (Joplin Tornado Survivor): To see so far in the distance and there be nothing, like someone dropped a bomb.
NARRATOR: NOVA follows the scientific investigation into the most dangerous tornadoes in recent times.
BRANDY PHILLIPS (Joplin Tornado Survivor): …something I don't want to have to live through ever again.
NARRATOR: Through survivors and their stories, scientists and engineers, we examine these devastating events and the effort to prevent future disasters.
JEFF SNYDER (Storm Chaser): There's more supercells dotted down the line, all the way through North Texas.
NARRATOR: …by deploying new technologies to warn people earlier in life or death situations.
GARY ENGLAND (KWTV, Oklahoma City): They, they love the weather here. Well, you know, if they don't pay attention, they die.
NARRATOR: The race is on to understand one of nature's greatest mysteries. Relive Oklahoma's Deadliest Tornadoes, right now, on NOVA.
It's a beautiful day in Oklahoma. The sun is up, the sky is blue; but suddenly, the weather takes a turn for the worse.
SHONBRAY JOHNSON (Moore Tornado Survivor): The weather's beautiful but then, just as you can snap your fingers it went bad.
NARRATOR: It's May 20, 2013. Tornado season is well underway, but it's been unusually quiet, until now.
GARY ENGLAND: It looked like it could be severe thunderstorms and some, some tornadoes.
GREG CARBIN (National Weather Service, Storm Prediction Center): The tornado watch was issued for a swathe of central Oklahoma. We know that that area will likely have a tornado, but we still don't know exactly where.
PAUL GOODLOE (The Weather Channel/Film Clip): So, we're concerned with the risk of tornadoes.
TV WEATHER REPORT: More severe weather possibilities.
NARRATOR: This darkening sky is about to bring chaos, death and destruction to the city of Moore. What is about to hit will be one for the history books.
GREG CARBIN: The thunderstorm formed to the southwest of Oklahoma City. I was very concerned.
GARY ENGLAND: That storm moved so quickly, it's like it created its own weather system. It created what it needed to grow.
HOWIE BLUESTEIN: We could see on radar, it began to produce a hook, and a vortex had been showing.
NARRATOR: Just before three p.m., all eyes turn to the heavens, as a funnel cloud drops towards the ground. It's a chilling sight.
MAN: There it is, there it is. It's forming. If it hits ground, it's a tornado.
NARRATOR: Soon tornado sirens are sounding all over the nearby city of Moore.
GARY ENGLAND: It was in its infancy stage. It was growing, and it was powerful, and all the energy speeding into it and the winds were ideal to produce a very large, deadly tornado.
It's just was that little ribbon and it was getting larger and larger and larger and larger. .
STORM CHASER: Okay, we are right up nearby it. Okay, I'm going to move the truck here a little bit. Hang on.
GREG CARBIN: …at three p.m. in the afternoon, then the tornado's on the ground, moving into Moore.
NARRATOR: The wind speed accelerates to 150 miles an hour, as it moves rapidly across country.
GARY ENGLAND: What was amazing to me was the rapid growth of a system from 65 mile an hour, all the way close to 165 mile an hour, in just a matter of minutes.
STORM CHASER: Oh, my god.
NARRATOR: This tornado will be on the ground for 40 minutes and will cut a swathe of destruction over a 17- mile path.
MAN: Holy moley! It's insane. It's huge.
NARRATOR: It's a large and deadly tornado, and it's getting stronger.
GREG CARBIN: Near the core of that tornado your wind speeds may be approaching 200 miles an hour, a giant violent circulation.
MAN: I hope everyone's okay.
NARRATOR: Within minutes, hundreds of homes are destroyed. Now, nature's fury has turned its sights towards even more vulnerable and precious targets. Briarwood Elementary School, in Moore, takes a terrifying hit as winds exceeding 200 miles an hour rip it apart. Miraculously, all its staff and children survive.
But at nearby Plaza Towers Elementary School, terror turns to tragedy as seven children die, despite the heroic efforts of their teachers to shield them from harm.
MAYLENE SORRELS: The building was collapsing on top of us, and we could hear glass shattering. We laid on top of our kids, and we did whatever we could.
STORM CHASER: Oh god, there's so much debris in the air.
NARRATOR: Soon afterwards, the tornado plows into the Moore Medical Center. The roof and upper floors are ripped from the building, but patients and staff survive.
MAN: This is right, right now. Part of the damage is along the 19th street in Moore, it's carrying on to… lane.
MAN: I think I have seen two cars get picked off the bridge and thrown in the air. This thing is violent. .
WOMAN: It's so big, I can't get the whole thing in my viewfinder.
NARRATOR: Finally, about 40 minutes after the tornado touched down, it clears the city limits, then, soon after, weakens and dies out.
MAN: Houses are leveled.
NARRATOR: In this city of almost 60,000, the tornado claimed 24 lives, including 10 children. Nearly 400 others were injured.
It left behind a trail of destruction and damaged or destroyed 12,000 homes.
SHONBRAY JOHNSON: I got trapped, when it came in and hit us. We made it out of there, we have some bumps and some bruises, but we have our life, and nothing is better than that. And I look at this as a testimony. I survived a tornado at the age of 28, I am able to walk, breathe and live. I may have a broken arm here, but God knows this, this right here, this is amazing.
TIFFANY KASPAR (Moore Tornado Survivor): All the kids are going crazy and screaming, and, like, I've got two of them on my lap, and the other two are holding me, and I've got my arm around my son, and he's like, "Mom, what do I do? I'm scared." And I was like, "Just pray.
JASON DOSHER (Moore Tornado Survivor): Last time my daughter saw her cat was Monday morning, before she went to school, and that was…now we've found her in the rubble.
You're going to bite my nose now, aren't you.
HOWIE BLUESTEIN: This was a disaster, because it had a direct hit on a densely populated area.
JANICE CHRISTIAN (Moore Tornado Survivor): My bathtub saved my life. We survived it in this tub, which, I must say, didn't have all this debris in it then.
I could hear it. You could definitely hear it, because one that size and the ground was just shaking like an earthquake, it was just shaking. And then I heard the cracking sound of the roof coming off the house, and then, I guess, the house, kind of, imploded.
NARRATOR: As battered Oklahomans emerge from the aftermath, scientists race to figure out exactly what happened.
Just 10 miles from Moore, Oklahoma, is the town of Norman, site of NOAA's National Severe Storms Laboratory.
Predicting and issuing timely advance warnings for tornadoes is the holy grail of scientists here. For them, the first step, after an event like this, is to understand exactly what happened.
Their instruments tell them that the Moore tornado had wind speeds exceeding 200 miles an hour, grew almost one and a half miles wide and stayed on the ground for about 40 minutes.
First estimates put the cost of the damage in excess of two billion dollars.
These terrible statistics make it one of the most damaging twisters on record. But even so, for a storm this size, the Moore tornado resulted in relatively few casualties. The fatalities were heartbreaking, but the toll could have been much higher. .
Many were spared because the tornado first touched down outside of town, giving residents time to get to safety. And advanced notice is essential to saving lives.
Meteorologist Greg Carbin coordinates warnings at the Storm Prediction Center, in Norman.
GREG CARBIN: I've been in meteorology for almost 25 years, forecasting, and it is mind-boggling to sit back for a moment and think about the advances that have been made in just that short period of time.
But the ability to forecast a tornado event with…prior to an actual thunderstorm forming is an ability we still don't have.
NARRATOR: Although almost every tornado begins with a thunderstorm, not all thunderstorms produce tornadoes. The difficulty is predicting which thunderstorms will be most dangerous.
GREG CARBIN: That's a double-edged sword in meteorology: you don't want to incite panic and, and, you know, talk doomsday scenario, but then again, you don't want to be so careful and quiet that people don't get the word.
NARRATOR: The hope of all tornado scientists is to be able to give as much warning as possible. But it isn't easy.
Meteorologists are able to predict thunderstorms days in advance, by satellites, weather balloons and radar, but tornadoes are born in minutes. The most effective prediction tool today is Doppler radar. It works by firing microwave pulses at raindrops to reveal their distance, speed and direction.
This distinctive hook shape often indicates that a thunderstorm has started to rotate and could spawn a tornado. It kick-starts the whole process of alerting communities at risk. When a tornado warning is issued, the amount of time that elapses between a warning and when the tornado strikes, if it does, is called lead time.
HOWIE BLUESTEIN: By lead time, we mean that the tornado will hit your place in X minutes.
NARRATOR: The amount of lead time was crucial to saving lives in Moore.
HOWIE BLUESTEIN: There could have been hundreds of people injured or killed in this tornado, had there not been good warning, and the people not known what to do in case a tornado was coming.
NARRATOR: Many people in Oklahoma have storm shelters, but most schools don't.
At the Plaza Towers Elementary School, the tornado took its most terrible toll. NOVA's cameras are the first to go inside.
In this school, seven children died when the storm tore through. But the tragedy could have been so much worse.
MAYLENE SORRELS: We had about 15 to 20 minutes to prepare for this, if that. We sat in the hallway, and you get on your knees, and you bend over your knees, and you put your hands behind your head. All of us teachers took a deep breath and it was like, trying to figure out, "Okay, what are we going to do now?" And we just hunkered over our kids, and we laid on top of our kids, and we did whatever we could.
NARRATOR: Four of Maylene's children were elsewhere in the school, including her daughter Tori.
TORI SORRELS (Moore Tornado Survivor): When it hit the one part of the school, I heard my teacher, Mr. Ayers, he screamed, "Get down! Get down! It's coming! It's coming! Get down!".
MAYLENE SORRELS: Then you hear the building being ripped apart, and you hear glass shattering, and you can't breathe, because it's blowing and sucking the air out of the room, and it felt like an eternity. The building was collapsing.
TORI SORRELS: Everyone started crying and screaming, and the next thing you know the roof comes off.
NARRATOR: In the immediate aftermath, Maylene saw the obliterated school, not knowing if her kids were alive or dead.
MAYLENE SORRELS: So we were shimmying out of there, trying to get up and make sure our students were okay. And, and they started screaming and, and crying, and we knew at that point that they were okay. And we, kind of, looked around and there was actually a car that had gone into the teachers that were over here with their students, and so they were pinned under rubble.
NARRATOR: After checking that her students were safe, Maylene frantically searched for her own four children.
MAYLENE SORRELS: I ran down to the other part of the building and climbed back in the building. It probably took about 30 to 35 minutes before I actually saw my children. That was probably the best feeling I had had all day. They just came running, and we embraced, and I told them that I loved them.
NARRATOR: After this tragedy, Oklahomans are discussing how to make schools safer, and scientists continue their efforts to understand these killer storms.
But like the weather itself, tornadoes are complex and varied. It's difficult to come to grips with the nature of these violent storms.
HOWIE BLUESTEIN: A tornado is a, a rapidly rotating column of air.
CHRISTOPHER WEISS (Texas Tech University): It's in connection with both the ground and also the, the base of the thunderstorm.
TIM MARSHALL (Haag Engineering): Cold air descends with rain and hail and wraps around the circulation.
ROGER A. PIELKE, SR. (University of Colorado): And if they concentrate that circulation in certain areas, you have a tornado.
NARRATOR: This is a typical tornado, spawned from rotating winds and a thunderstorm called a supercell. Most tornadoes are small and broken, with wind speeds less than a hundred ten miles an hour. The most extreme tornadoes are two miles wide, with 300-mile-an-hour winds and capable of travelling hundreds of miles.
HOWIE BLUESTEIN: We certainly know what a tornado is. However, the big mystery is trying to discover why a tornado forms. We don't understand why some thunderstorms produce tornadoes and others don't.
Only a very small fraction of them, 10 percent or perhaps even, even fewer storms go on to produce tornadoes.
NARRATOR: Important clues can emerge from studying the pattern of destruction. So amid the aftermath of the Moore tornado, Howie Bluestein takes to the skies.
HOWIE BLUESTEIN: From the air, you can really see it. From the ground, you just don't get a, an appreciation for it. Now we're passing through the damage again. You get the damage path three houses wide for "heavy damage.".
Oh, this is just awful to, awful to see.
This must have been where the tornado was its most intense and where the tornado was its widest…a world class tornado, I think.
NARRATOR: And this isn't the first time that the people of Moore, Oklahoma, have experienced this kind of death and destruction.
May 3, 1999, and one of the most powerful tornadoes on record makes a direct hit on the city. Winds, topping 300 miles an hour, destroy 8,000 homes, causing a billion dollars' worth of damage and leaving 46 dead.
In May, 2003, the unthinkable happens again. Another major tornado heads straight towards Moore. Although no one is killed, dozens are injured, and homes, businesses and factories are wrecked.
GREG CARBIN: Here is a composite of the three significant tornadoes to strike Moore in the last 15 years.
NARRATOR: All the radar images have one striking feature in common: a distinctive hook showing that the clouds are rotating, the precursor of a tornado.
Gary England, chief meteorologist of Channel 9 TV, has decades of experience issuing vital warnings in the state where tornadoes strike terrifyingly often.
GARY ENGLAND: Geographically, we're right in the right spot. Somewhere, there has to be a point that is most favorable. And apparently, based on history, it looks like it's in Moore, Oklahoma.
NARRATOR: For whatever reason, Moore seems to be ground zero in what is known as Tornado Alley, the central portion of the country, between the Rocky and Appalachian mountains.
Every year, from mid-April into the summer, Howie Bluestein ventures out into this vast expanse, chasing tornadoes with his advanced mobile radar. His goal is to understand the inner workings of tornadoes, and this is his lab.
But what is it that makes this region so dangerous at this time of year?.
It starts with cold winds coming in.
HOWIE BLUESTEIN: During the springtime, we have air coming in at high levels in the atmosphere. It comes in, and it goes up and over the Rocky Mountains and it subsides, and it warms. And that makes southerly winds out over the central part of the United States.
And those southerly winds bring in a relatively warm and moist air off the Gulf of Mexico and overspreads the plains area.
NARRATOR: This creates huge thunderstorms. Then winds coming in from different directions produce spin.
HOWIE BLUESTEIN: The winds turn with height, and they become a lot stronger with height. So we have a source of rotation within the storm.
NARRATOR: The Moore tornado is noteworthy, partly because it appeared in a relatively quiet season. 2012 was also quiet, likely due to drought conditions. But 2011 was the fourth deadliest tornado season on record.
In April, the start of that season, Howie Bluestein and his team are out in the plains of Oklahoma, testing their new mobile Doppler radar. So far, all is quiet. But a hundred miles away, in another part of Oklahoma,.
STORM CHASER: I'm calling to report a tornado, it is on the ground, just west of Stroud.
NARRATOR: …a tornado touches down in Stroud, the first of many in this area.
STORM CHASER: Oh, no! Oh, no!.
NARRATOR: The average tornado lasts two to three minutes, but some keep going for 10 minutes and even longer.
STORM CHASER: Whoa, that's violent. That's incredible.
NARRATOR: Over several hours, Alabama, Arkansas, Mississippi, Oklahoma and North Carolina are all struck by tornadoes.
A strong storm over Tushka, Oklahoma, starts to rotate, becoming a tornado, killing two people.
But that's just the beginning. Over two days, over 200 tornadoes touch down in 16 states. Thirty-eight people lose their lives, from Texas to North Carolina. This is a shocking start to tornado season, described as one of the largest single system tornado outbreaks in U.S. history. Scientists are asking, "Is it an isolated incident or part of a pattern?.
GREG CARBIN: We saw a number of these events. We saw, around the 16th of the month, a major tornado outbreak in North Carolina. The questions became, can we predict that this pattern will continue.
NARRATOR: To answer that question, Greg compares the April 2011 outbreak to previous seasons.
GREG CARBIN: We have, actually, have a system that will take a forecast and it will compare that forecast to historic weather events of the past, and so there was a good analogue for this event that had occurred in the past to the forecast pattern that was coming up in the days ahead.
NARRATOR: When Greg examines his data, the result is not reassuring.
GREG CARBIN: The match that came up was a Veterans Day event of November, 2002: nearly 40 fatalities associated with that event; kind of an unusual time of year, not the spring, but actually the second, what we call the second season of activity.
NARRATOR: Fall, 2002, saw 76 tornadoes sweep through 17 states. Greg is concerned that the position of the jet stream, the river of air that circles the earth high in the atmosphere, is affecting the weather. It's shown here in blue.
GREG CARBIN: This is the November jet stream pattern that was in place in the year 2002. And we can see the similarities with this event in 2011: jet stream diving across the Rocky Mountains, driving intense thunderstorms across the southeast Tennessee Valley and Ohio Valley.
I sent email out to the National Weather Service—publicly available through our website—talking about the fact that the upcoming event showed signs of similarity to the outbreak that we saw in November, 2002.
NARRATOR: There's cause for concern. Some meteorologists believe it could be even worse than the 2002 Veterans Day outbreak. A tantalizing clue lies off the coast of Peru.
The eastern Pacific, July, 2010: Ocean buoys record unusually cold sea surface temperatures. This is called "La Niña," and for centuries, Peruvian fishermen have been aware that it not only affects their fishing, but also the weather.
Scientists can now measure the effect. Here's the way a La Niña looks on a satellite's thermal imaging camera, showing the cooler sea temperature off the coast of Peru in green. Scientists discovered that the huge expanse of cool La Niña water could affect the surrounding atmosphere and the jet stream, shifting severe weather into new areas, and intensifying it in places like the southern United States.
ROGER PIELKE: We had a very strong La Niña in the wintertime that set up a strong jet stream that provided the wind speed energy that was necessary to generate thunderstorms, but we also, then, had very humid and moist air in the southeastern part of the United States that provided the fuel for these thunderstorms. And the combination of those two provided an environment that was more conducive to these large tornadic outbreaks than you might have in other years.
NARRATOR: By spring, 2011, the newly intensified jet stream was already contributing to rainfall and floods across the south, plus droughts and raging wildfires in Texas, warning signs of historic weather extremes.
ROGER PIELKE: We were worried about it, because when you have a La Niña, as our research has shown, there tends to be more family outbreaks of these tornadoes in the southeast United States.
NARRATOR: In fact, one of the worst tornado events in history, the "Super Outbreak" of April, 1974, also took place in a La Niña year. A hundred and forty eight twisters touched down in 13 states, from Mississippi all the way up to New York, killing 330 people and injuring thousands.
But will the pattern hold in 2011.
STORM CHASER: It's crossing the interstate right where we were.
NARRATOR: On April 25th at 7:25 p.m., violent storms in Vilonia, Arkansas launch the largest outbreak ever recorded.
STORM CHASER: Here comes the rain. Whoa.
NARRATOR: The worst day is the 27th of April, starting at 2:30 p.m.
Radio News Clip: A large, violent tornado is down on the ground.
NARRATOR: A powerful tornado touches down in Philadelphia, Mississippi, and kills three people.
Then Cullman, Alabama, is struck, leaving six dead; followed by Hackleburg, Alabama; 18 are killed.
4:45 p.m., Tuscaloosa, Alabama: classic anvil-shaped clouds form supercells, thunderstorms where rotation has begun, as Greg Carbin observes.
GREG CARBIN: I came out into operations, during the, during the late afternoon. You were seeing incredibly well-formed supercells, the likes of which was truly stunning.
NARRATOR: A distinctive hook echo, the radar signature of a fiercely rotating storm, heads toward Tuscaloosa.
GREG CARBIN: With every one of those hook echoes, you had a violent tornado on the ground.
STORM CHASER: This is a large, violent tornado coming up on downtown Tuscaloosa. Be in a safe place right now.
NARRATOR: A mile-and-a-half-wide tornado cuts through the heart of Tuscaloosa, leveling entire blocks and tossing trees and power poles around like toothpicks, tornado scientist Chris Weiss recalls.
CHRIS WEISS: The storm that affected Tuscaloosa actually initiated back in Mississippi, actually travelled for, like, a good hour and a half and then produced its tornado; stayed on the ground all the way up into Birmingham. The storm itself actually lasted seven and a half hours, because of the various dynamics, with the storm producing tornadoes along a good chunk of that length. You see regions all across northern Alabama, into northwestern Georgia, even up into western North Carolina. Tennessee was also affected, so a tremendous number of tornadoes, for this outbreak.
NARRATOR: In Oklahoma City, TV meteorologist Gary England follows the path of the storms on radar.
GARY ENGLAND: We watched them from here. You can look at the radars, and you could see the tornadoes developing, you know, massive supercell thunderstorms, big, big rotations inside. The rotation sometimes becomes the entire tornado and that's what was happening down there, and it looked like a fleet of them coming across it.
NARRATOR: The outbreaks of 2011 gave tornado experts vital information about the devastating power of wind. Although disaster investigator Tim Marshall sees it often, he's is always shocked.
TIM MARSHALL (Haag Engineering): I have always been surprised by the power of tornadoes. I mean, after all, all it is air and water, so how dangerous could that be.
NARRATOR: Investigators like Tim use a system called the EF-scale to measure the strength of tornadoes by rating the damage they do.
TIM MARSHALL: Typically, every year we get 1,500 tornadoes in the U.S. An EF-0 is damage to tree limbs, some shingles off of a roof or so. And then EF-1 is more substantial damage, like some roof decking.
NARRATOR: An EF-1 can often be powerful enough to overturn a mobile home.
TIM MARSHALL: EF-2 the roof has gone.
NARRATOR: The aftermath of even an EF-2 can look like a bomb exploded.
TIM MARSHALL: EF-3 is basically the outer walls of the house are down, and only the interior walls remain.
NARRATOR: An EF-3 releases the same energy as 10 tons of T.N.T., like the tornado that hit Canton, Oklahoma, in 2011.
TIM MARSHALL: EF-4 is basically all the walls are down, with just a pile of debris left on the foundation.
NARRATOR: Very little is left standing after an EF-4 tornado. This EF-4 hit Shawnee, Oklahoma, May 19, 2013.
TIM MARSHALL: And EF-5 is complete sweeping clean of the foundation of the house, of all the belongings, such that there's only a little perimeter left in the ground where the house once was.
NARRATOR: And an EF-5 is equivalent bomb damage to the atomic bomb dropped on Hiroshima.
TIM MARSHALL: To have an EF-5 go through a major metropolitan area is rare. Less than one percent of all tornadoes get to be that strong and get to produce that kind of intense damage.
NARRATOR: But EF-4 AND EF-5 storms combined, just one percent of all tornadoes, produce 70 percent of all casualties.
The tornado that hit Moore in 2013 was categorized as an EF-4 at first. It was later upgraded to an EF-5.
So what led to this massive tornado? There were no cold La Niña conditions in the Pacific, but earlier the jet stream had shifted further south than usual. When it finally moved back north, it allowed warm, moist air from the Gulf of Mexico to surge across the Oklahoma plains, perfect fuel for supercell thunderstorms that spawn tornadoes.
JOHN WILSON, JR. (Moore Tornado Survivor?): We will rebuild. We will stay here. We're not going anywhere. This is our home. .
NARRATOR: This one killed 24 people, a stark reminder of the need to increase lead time to get people to safety.
It used to be a lot worse,.
MAN: There's a clear wedge tornado, Gary, about a quarter-mile-wide wedge tornado.
NARRATOR: …as Gary England recalls.
GARY ENGLAND: You know, when I first came here, in 1972, the lead time on how early could we get a tornado warning out, it's probably about minus-two minutes. The warnings in those days were just absolutely terrible. Equipment wasn't too good, the radars were nice, but just nothing to go with them, no computers. And I can only warn you, because it blew someone else's house away, down the street. That's how bad the warnings were.
NARRATOR: This 1950s government film on tornadoes illustrates how limited tornado warnings were.
1950s FILM FOOTAGE ("Tornado," Calvin Productions): I'm going to keep watch on the southwest side. It's where most of them come from.
WOMAN IN FILM: Do you think it's likely.
MAN IN FILM: No, the odds are way against it, even in weather like this.
NARRATOR: Forecasters had to rely on ground observations and weather balloons to tell them if storms were coming. In the 1960s, satellites were launched to observe cloud formations and give readings of Earth's temperature.
But when Doppler radar was introduced, in 1973, scientists could clearly see the hook echo, signaling that rotation had begun. Powerful computers that could analyze vast amounts of data helped get the tornado lead time to today's 13-minute average. This has saved many lives, but could it be better.
Most forecasters believe that a breakthrough will come only by unlocking more detail on exactly how a tornado forms.
Howie Bluestein and his team intend to do just that. They've installed a new Doppler radar to carry on their truck. If they catch a tornado, it could get them enough data to refine the computer models that they use to predict future storms.
HOWIE BLUESTEIN: What people are trying to do is to take weather data and put it into a numerical model and then let the numerical model produce tornadic thunderstorms. So, then, you can issue a forecast and say, "There's a 20 percent chance that in your neighborhood, four hours from now you might get a tornadic thunderstorm.
NARRATOR: The main question concerns rotation, as Chris Weiss explains inside a tornado simulator at Texas Tech.
CHRIS WEISS: To get a tornado, we need that storm to acquire supercell attributes. And that just means that the wind is coming from different directions and speeds, with height.
NARRATOR: The supercell storm starts with air crashing and spinning, mostly in a horizontal direction. To turn into a tornado it needs to go vertical.
CHRIS WEISS: We need to have an updraft, an area of very quickly moving air, pulling the air upwards very quickly. And what that does is it takes the spinning air, and it stretches it in the vertical. So you can imagine that, say, you had one of those Chinese finger trap toys, and you pull on it on both ends, it constricts that access of rotation. It makes it spin faster. That helps us explain most of how tornadoes form, though we don't have a good handle, necessarily, on, on the mechanisms that create that spin near the ground, though. That's where a lot of the research is focused at the moment.
NARRATOR: So, vertical spin is only part of the picture. What else can turn a rotating thunderstorm into a tornado? If scientists can work out other possible factors, like wind speed, temperature and pressure, they may be able to, in effect, "reverse-engineer" a tornado.
HOWIE BLUESTEIN: This is a supercell that's moving to the southeast. I cannot discern any rotation, visually, but we need to keep a, keep an eye on that.
NARRATOR: Out on the plains of Oklahoma, in late April, Howie is hoping to get close to a tornado with his new generation of mobile radar equipment. This is dual-polarization radar, a state-of-the-art system for peering more closely than ever before into the heart of a tornado.
The vital new development is that this radar can spot, not only raindrops, but also debris blasted into the air by a tornado funnel.
Howie's system is a mobile one, but dual-polarization radar is so effective that it has now been installed throughout the network on fixed radar stations.
HOWIE BLUESTEIN: Dual-polarization radar can tell us information about the stuff that the radar beam is scattering off. So we can tell a small raindrop from a big raindrop, from a hailstone, to a flying cow, to a piece of, of flying board.
That's extremely important from the standpoint of warnings, because if a radar operator sees that, not only is there a vortex, but there is an indication of debris, then you can be pretty sure that there is a vortex acting on the ground.
NARRATOR: 2011 gives Howie the opportunity to try his new equipment, but first he needs a tornado.
HOWIE BLUESTEIN: There's a funnel cloud due west of us; doesn't appear to be very intense. There are also a cluster of three cells to our northwest, and they look fairly good on radar, not great. So, we're just going to sit here and wait.
Oh, wow. Holy mackerel, we've got three hooks. We have three hook echoes, right now, three potentially tornadic storms.
NARRATOR: The team has managed to place the radar in the path of a storm, picking up hook echoes, which signal the storm is beginning to rotate.
HOWIE BLUESTEIN: And the southern one is coming fairly close towards us. It's a good thing we stopped.
NARRATOR: It looks like it could be evolving into a tornado.
HOWIE BLUESTEIN: Hope we don't have to move.
NARRATOR: Half an hour later, the tornado is forming, and Howie's radar is recording it all.
HOWIE BLUESTEIN: This has never been done before, a relatively complete look at the evolution of the tornado as it was beginning, as it was intensifying, as it became very strong.
NARRATOR: Then, one of the most active seasons on record seems to die out, just at this point. .
GREG CARBIN: After a record April, as far as tornado events, we were headed for a record May, as far as the fewest tornado events on the record, and then Joplin.
NARRATOR: Joplin, Missouri, May 22, 2011.
STORM CHASER: Oh, my gosh. Oh, my gosh.
NARRATOR: The deadliest tornado since 1947 emerges from some unique weather conditions,.
TIM MARSHALL: The thunderstorm that produced the Joplin tornado began in Kansas.
NARRATOR: …forming at 2:30 p.m.
TIM MARSHALL: Southeast winds came in from the surface, and up aloft there was southwesterly flow. And this action, here, produces a spin.
NARRATOR: Then, higher than normal ground temperatures produce an updraft of hot winds.
TIM MARSHALL: And that updraft tilts that into the vertical and produces this counter-clockwise rotation.
NARRATOR: At 4:15 p.m., rain and hail begin to fall.
TIM MARSHALL: Cold air descends with rain and hail and wraps around the circulation. And as it crossed the state line between Kansas and Missouri, just west of Joplin, a tornado was born.
NARRATOR: The tornado is spotted on the ground at 5:34 p.m.
STORM CHASER: It's a massive tornado, just massive destruction.
WOMAN: Oh, these poor people.
MAN: I know.
MAN: You've got to understand, Joplin's gone. It's like a gale F4.
MAN: It's gone, it's gone.
WOMAN: There's people in there.
MAN: I know, come here.
WOMAN: People everywhere.
MAN: Hello! Hello.
NARRATOR: It also left more than 150 people dead and was the costliest tornado on record, causing damage worth 2.8 billion dollars.
On the ground, Tim Marshall studies the debris for any evidence the winds left behind.
TIM MARSHALL: I look for clues that indicate how strong the winds were. So that weighs many hundred pounds right there. The heavy weight of this concrete parking curb, being moved like that, tells us that the low-level winds were very strong.
NARRATOR: The Joplin tornado is so powerful it twists the local hospital four inches off its foundation. Most houses suffered much greater damage.
TIM MARSHALL: The tornado's only in contact with the house for a very short period of time. I mean, this all happens in 30 seconds to a minute, so the heavier your building, the better, and the more apt that you're able to survive it. If you're inside a car, and you're close to a window, you can be sucked out of the vehicle by the differential pressure.
NARRATOR: Even light materials on the loose can be deadly.
TIM MARSHALL: Now, a piece of cardboard's pretty flimsy, but if a piece of cardboard is travelling at 200 miles an hour, then it can go right on through things like this; it can go right on through the human body.
NARRATOR: The tornado that hit Joplin, killing more than 150, was rated as an EF-5. In contrast, the Moore tornado of 2013, also ranked as an EF-5, killed only 24. Since that tornado struck, scientists have been trying to understand what accounts for the difference in the death toll.
One the most important factors may be the people themselves. Living in the heart of Tornado Alley, the people of Oklahoma are used to living with tornadoes.
Many have storm shelters or safe rooms, and they take warnings seriously.
GARY ENGLAND: Oklahomans are very aware of what's going on in the weather. They stay weather-aware. I think most of the audience understands what we're talking about. Because a lot of times I'll say we have a big supercell, they know that's a rotating thunderstorm usually. And usually a, a supercell has that rotation in it, I think they understand them. They, they love the weather here. Well, you know, if they don't pay attention, they die.
JIMMIE ZIMMERMAN (Oklahoma Tornado Survivor): I went to the TV, turned it on, and Gary England was on there.
GARY ENGLAND: (On Air) Right now, it's along and just north of Interstate 40.
JIMMIE ZIMMERMAN: They were tracking the tornado. So, I went to the kitchen window, and I looked out, and I saw it. And that's the first tornado I've ever seen in my life.
GARY ENGLAND: (On Air) I strongly suggest you take your tornado precautions; this thing has produced a huge tornado.
JIMMIE ZIMMERMAN: I went to the safe room, and I was in there maybe 30 seconds, when it hit.
NARRATOR: The safe room in this house saved the lives of eight people.
JIMMIE ZIMMERMAN: The way the safe room is designed, the structure of it, to tie the structure of the house together is the reason these walls are standing right now.
NARRATOR: Even in the latest 2013 disaster, Gary's warnings would play a vital role.
SHONBRAY JOHNSON: The first time that we saw the tornado or heard about the tornado touching down was with Gary England on News Channel 9. They just said, "Tornado down, tornado down! Everybody needs to take shelter. If you are not underground, you will not make it.
GARY ENGLAND: What was amazing to me was the rapid growth of the system from, basically, an EF-0, probably 65 miles an hour, all the way close to 165, 150, 165, in just a matter of minutes.
NARRATOR: Staff at the Moore medical hospital scrambled to move patients and staff to safety.
Through her office window, nurse Shonbray Johnson could see the tornado heading directly towards them.
SHONBRAY JOHNSON: This, right here, is actually our waiting room. If we did not move the patients, they would clearly be dead right now.
I got trapped when it came in, and it hit us. We were stuck in a little pocket, enough for us to be able to breathe. We still had our phones so we called 911. So I just started kicking walls, and I just heard someone say, "I hear something. If you're down there, scream.".
NARRATOR: Amidst the devastation, Shonbray bumped into the savior who answered her cries for help.
SHONBRAY JOHNSON: Thank you so much. Oh, god.
We did not think we were going to make it out of that building. I was able to walk away. It was a relief to my children when I saw them, so, it's a blessing.
NARRATOR: The collapse of hospitals, homes and schools in Oklahoma has highlighted the need to strengthen buildings to withstand deadly tornadoes. So, by simulating the effects of tornadoes, scientists at Texas Tech are trying to make structures more robust. .
DARRYL JAMES (Texas Tech University): It boils down to cost. We could design a building or structure that would withstand a tornado. The problem is that most of us couldn't afford to live in that structure.
The tornadoes that we simulate, in here, are based on the mid-EF-3 range, because about 92 to 94 percent of all tornadoes fall in that range. The reason why we're doing that is we would like to understand the, the wind-loading on structures, such as this scale model of a mobile home. Our preliminary work shows you have parts of the structure that experience a positive force. In other words, they're trying to push the force in, and then, as a tornado gets closer and closer, then you have, suddenly, parts of the force wanting to pull it apart. The other bad part is you have stuff falling down from your roof.
NARRATOR: Structural engineers at Texas Tech are also looking at debris impact, trying to replicate the forces of the worst tornadoes, like the EF-5 that hit Moore, Oklahoma.
LARRY TANNER (Texas Tech University): Tornadoes can send all kinds of debris, impaling buildings, livestock, people, cars. It's, it's phenomenal.
DARRYL JAMES: Ultimately, we would like to develop codes that say, if you live in these tornado-prone areas, you ought to think about reinforcing structures in this way or building a structure in this certain way. That's the ultimate goal.
NARRATOR: As the 2013 tornado season, with the devastating Moore disaster, winds down, scientists and communities at risk are grappling with further questions.
Will destruction at this scale become more frequent.
TIM MARSHALL: And the reason why tornado disasters are on the upswing is that more people are getting in the way. As our cities expand, the target gets bigger. So, tornadoes are more apt to hit major cities now than they were a hundred years ago, and that can only increase in the future.
NARRATOR: And does global climate change mean it's going to get worse?.
HOWIE BLUESTEIN: As the climate warms up and the amount of moisture near the ground increases, that certainly is something, which is favorable for producing more thunderstorms.
GREG CARBIN: Probably, there's a relationship, on the large scale, to a warmer climate. We also know that there's a potential for more moisture in a warmer atmosphere, and we are seeing extreme precipitation events occur more frequently due to that.
NARRATOR: The Moore, Oklahoma tornado was a major disaster, the first EF-5, top-of-the-scale tornado to strike the U.S. in two years. The loss of life will never be forgotten, yet it was less than might have been expected.
Tornado awareness, better shelters and increased lead-time will continue to save lives. Research on Oklahoma's plains and new scientific equipment promise further improvement. No human force can ever prevent tornadoes, but a better understanding of them may yet soften the toll from these winds of almost unimaginable power.
IMAGE CREDITS (main image) © Paul Hellstern/AP Photo
- Howard Bluestein, Greg Carbin, Janice Christian, Jason Dosher, Gary England, Darryl James, Shonbray Johnson, Tiffany Kasper, Tim Marshall, Roger A. Pielke, Maylene Sorrels, Tori Sorrels, Larry Tanner, Christopher Weiss, John Wilson Jr., Jamie Zimmerman