Hunt for the Supertwister

Hunt for the Supertwister

PBS Airdate: March 30, 2004

NARRATOR: It's early May, and an ugly storm is bearing down on Oklahoma City. In times like these, people turn to their TV weather forecasters, especially local legend Gary England.

From the control room, Gary watches in horror, as the heavy, roiling atmosphere cooks up a deadly surprise.

GARY ENGLAND (KWTV, Oklahoma City): Priority One! Priority One! Tornado warning for the... area. Get Bobby on...

NARRATOR: This isn't just any tornado. It's one of the most violent and destructive forces of nature: a supertwister.

GARY ENGLAND: This is a major tornado. Wind speeds? We don't know. But it's going to level most houses. Get below ground immediately.

NARRATOR: The date was May 3, 1999, and one of the most powerful tornadoes on record had made a direct hit on the suburbs of Bridge Creek and Moore, Oklahoma: 8,000 homes destroyed, one billion dollars of damage, 40 dead.

This is what happens when a column of spinning air blows faster than 300 miles an hour.

JOSH WURMAN (Center for Severe Weather Research): A 250 or 300 mile an hour wind can only be compared to those that might be experienced on the fringes of a nuclear explosion.

TIM MARSHALL (Engineer/Meteorologist): A 300 mile an hour wind is not three times as strong as 100 miles an hour; it is nine times as strong.

NARRATOR: Most tornadoes strike the American heartland, but no place is safe. In 2002, a supertwister struck Maryland, just south of Washington, D.C.

TIM MARSHALL: If you were to have taken the La Plata, Maryland tornado, and just moved it north about 30 or 40 miles, you would have gone from beltway to beltway, right across the Potomac and through the Nation's Capital.

NARRATOR: For decades, storm chasers have been stalking the supertwister, trying to unlock its deadly secrets. Now, armed with a slew of high-tech gadgetry, scientists are probing deeper than ever before and creating their own tornadoes inside a computer.

Will they finally win the battle against one of nature's most terrifying killers? Hunt for the Supertwister, right now on NOVA.

Major funding for NOVA is provided by the Park Foundation, dedicated to education and quality television.

We see 400 employees in three years. At Microsoft, your potential inspires us to create software that helps you reach it. Your potential, our passion.

Science: it's given us the framework to help make wireless communications clear. Sprint is proud to support NOVA.

Major funding for NOVA is also provided by the Corporation for Public Broadcasting, and by contributions to your PBS stations from viewers like you.

Thank you.

NARRATOR: Moore, Oklahoma, just outside Oklahoma City, may look like an ordinary American town, but it has a disturbing and violent history, because this quiet community has a habit of attracting tornadoes.

MAN: The gas lines have been busted.

NARRATOR: The town was hit by major twisters two years in a row, in 1998 and again in 1999. In May 2003, the unthinkable happens again. Another major tornado heads straight toward Moore. This time, the spinning vortex makes a beeline for Mama Lou's Diner.

RUTH: Well, we were sitting out here having dinner, and my daughter called and said that a tornado was coming our way.

SUSAN: And the manager told us we needed to either leave or stay and get in the freezer walk-in.

RUTH: There was a young waitress. She went in. My husband was standing right in front of her. He said she was shaking so bad, he could feel her tremble behind him. I sat in this chair. Things happened so fast and people moved so fast, and the man in the wheelchair...we couldn't get this door to shut.

SUSAN: When the tree came through the hallway, we just fell kind of backwards, and it was over with. We walked out, and the walls were gone, everything was gone. The ceiling was in. There were people laying everywhere, on the highway and in the ditches, bleeding, but we were all alive. It was amazing. Amazing.

NARRATOR: Like the diners in Mama Lou's, many residents of Moore heard about this tornado just a few minutes or even seconds before they were hit.

DON STALEY: Yeah, I was watching the tornado with the AC/DC TV here.

NARRATOR: Don Staley headed for the aboveground concrete safe room he installed after twisters damaged his house two years in a row.

DON STALEY: I just felt the vibration of the ground, and about 10 minutes later opened the door, and the house that destroyed, but I knew I could pick up the pieces and go on with my life.

NARRATOR: As Don sat watching it on TV, the tornado destroying his home had not even reached full strength. Just a few minutes later, the storm tore the side off the GM plant and leveled the union hall.

Many fear that scenes like this are a sign of things to come, that we haven't seen the worst that tornadoes can do.

TIM MARSHALL: I think we have reached a critical point here, where we are now expanding our cities bigger and bigger, so the targets for tornado hits are getting bigger and bigger. And the fear that I have is that now...that the cities are going to continue to get bigger—the houses still stay the same in terms of construction—now we're going to start having an upswing in the number of fatalities.

GARY ENGLAND: Let's just picture this. Let's say it's two o'clock in the afternoon, large tornado comes into a city, moving toward a school that has 500 children in it. What's going to happen when that warning goes out? There's going to be hundreds of parents trying to rush to that school to get those kids out. And it will take the school out. It will take the parents out. And mark my words, it will happen.

NARRATOR: Tornadoes are freak events of nature. They can't be stopped, but if we want to survive them, we've got to predict when and where they'll occur. But tornadoes continue to defy forecasters.

Other violent storms, like hurricanes, are huge—covering thousands of square miles—and show up on radar and satellites long before they strike. Tornadoes are another story. Compared to hurricanes, they're tiny. And they form quickly. But killer tornadoes don't just appear out of nowhere.

Every spring, warm, moist air surges up from the Gulf of Mexico, pushing into cool, dry air from the north. The warmer air fuels thunderstorms that rise into the upper atmosphere, sometimes growing into immense rotating giants known as supercells. A swirling column of air develops inside the storm, narrowing and reaching down toward the ground, becoming a tornado.

Over a thousand tornadoes touch down in the United States each year. In some, a narrow funnel cloud waves and bends like an elephant trunk, while others grow wide, enveloped by rain and clouds.

Most tornadoes are weak and disappear within minutes. A quarter of all tornadoes have the potential to cause significant damage. A rare few unleash the enormous energy stored in the atmosphere, generating ground-level winds above 200 miles per hour, and traveling dozens of miles.

MAN: He's going to drive into it if he's not careful.

NARRATOR: Rated F4 and F5 on a five-point scale, these are the deadliest of storms, the supertwisters.

GARY ENGLAND: They do happen, and they happen nearly every year. And of course, if an F5 comes down your street, if you're not in a safe room or a basement or a cellar, you're probably going to be history.

NARRATOR: The first line of defense against severe weather is the National Storm Prediction Center, in Norman, Oklahoma. But unfortunately, even these scientists can't predict exactly where and when a tornado, or even a thunderstorm, will strike.

STEVE WEISS (Storm Prediction Center): We don't have a very good picture of the potential of thunderstorm activity and exactly where it might be able to develop. We all wish that we could pinpoint the exact location where severe weather will strike and tell people what time it's going to strike, but the science hasn't reached that point yet.

NARRATOR: The storm center monitors the atmosphere across the entire continent and then uses computer programs to try to predict where the most dangerous storms will develop. If general conditions look strong for tornadoes, the storm center issues a tornado watch, often covering tens of thousands of square miles.

Only after radar suggests a tornado is forming does an official tornado warning go out.

BARBARA WATSON (National Weather Service): When we issue the warning, the warning is supposed to mean that that tornado has been detected, it is there. We want to be able to take it to that next step where we can say, "We've got this really bad storm. Conditions where that storm is headed are ripe for a tornado to develop."

Where we're at right now, when you've detected it, it's occurring!

NARRATOR: Official tornado warnings often come too late, on average, only 12 minutes before a twister strikes. And frequently, they're false alarms.

One man believes we can do better.

KELVIN DROEGEMEIER (University of Oklahoma): My dream is to be able to detect tornadoes down at very fine scales, to anticipate tornadoes a half an hour before they occur. We're talking about a storm forming to produce a tornado over a county or a city. It's a whole different ballgame.

NARRATOR: Kelvin Droegemeier is a meteorologist who wants to overhaul our current system of detecting tornadoes.

KELVIN DROEGEMEIER: We need to see closer down to the ground. That's where the weather really happens. I mean the storms up in the atmosphere, they're the ones that eventually cause the weather, but the stuff that's actually affecting society happens down near the ground, where we don't really observe things very well.

NARRATOR: Today's system relies in part on a network of Doppler radar. Doppler can sense the movement of air and moisture in remarkable detail.

Used as long-range radar, Doppler dishes are spaced 100 miles apart or more. Gazing out over the horizon, they can't see what's happening close to the ground, where tornadoes form.

TIM MARSHALL: There's a limit to tornado prediction, and I believe we have reached that limit right now. With all the available information that we have, radars are only put at certain locations. They're not everywhere. Radars that we have can scan out 100 miles, but at 100 miles they're only scanning the top part of the storm, and so they're not seeing down low.

NARRATOR: Kelvin Droegemeier dreams of a world filled with Doppler dishes hung on cell phone towers and all kinds of buildings, just 20 miles apart. This Doppler-rich world could paint a much more detailed picture of the weather, maybe even catch tornadoes in the act of forming.

KELVIN DROEGEMEIER: We want to put a few of these radars out there to make sure that if a tornado is beginning to form, we know absolutely, for certain, that it's going to happen, and we can tell you that 30 minutes ahead of time—whether it's a weak tornado, a strong tornado; whether it's in December or March or May.

NARRATOR: Kelvin is now wiring central Oklahoma with an experimental network of small radars, confident that his plan will someday revolutionize the forecasting of tornadoes, including supertwisters.

But others aren't so sure.

HOWIE BLUESTEIN (University of Oklahoma): You might be able to predict that a storm may or may not form, you may predict that some storms may be more likely to produce strong tornadoes than others, but we may never be able to predict that a given storm in a given location will go on to produce a tornado.

NARRATOR: Howie Bluestein's skepticism comes from over 25 years chasing down storms in the twister-prone region of the central plains, known as Tornado Alley. When he started out, Howie's operation was certainly low-tech. There were no laptop computers, no global positioning system...

HOWIE BLUESTEIN: Small seepings building up under the anvil.

NARRATOR: ...no cell phones.

HOWIE BLUESTEIN: I'm a little bit worried about something happening right back just south of Norman.

NARRATOR: Over time, the storm chaser's arsenal has expanded. Howie was the first to put a radar dish on the back of a truck and capture crucial data of tornadoes in action. But even with today's tools, storm chasers like Howie consider themselves lucky if they intercept one or two good tornadoes each year, because the thunderstorms that spawn them are extremely complex creatures.

HOWIE BLUESTEIN: Whether a thunderstorm forms in one county or the next county could depend upon differences in wind that you can barely detect with instruments, or changes in temperature and humidity that are barely detectable.

NARRATOR: And Howie knows just how far we are from understanding the true nature of tornadoes.

HOWIE BLUESTEIN: We still haven't solved the problem yet. We still haven't figured out exactly why tornadoes form.

NARRATOR: For all their long years of study, storm chasers are forced to admit that the exact chain of events that turns a thunderstorm into a tornado is still a mystery.

JOSH WURMAN: We know that supercell thunderstorms make tornadoes, but we also know that most of them don't.

NARRATOR: Josh Wurman is one of Howie's colleagues and a fellow storm chaser.

JOSH WURMAN: Only about 20 percent or 25 percent of supercell thunderstorms produce tornadoes. And only perhaps one percent to five percent of those produce what we call significant tornadoes, the large ones, the long-track, the ones that do 90 percent or 95 percent of the damage and fatalities.

MAN: Okay, down two. Stop here, near the hill, and start scanning.

MAN: I feel like we're in a twister movie.

NARRATOR: Josh has witnessed some of the most powerful supertwisters of recent years, including the May 3, 1999, storm that hit Moore, Oklahoma, where he recorded the fastest winds ever measured: just over 300 miles per hour.

When the massive supertwister first set down, it was in a field about 40 miles from Moore. TV forecaster Gary England had a full hour to warn his audience.

GARY ENGLAND: Do not try to ride this storm out in your home, unless you are trapped. Get in the center part of your house, a closet or bathroom. Cover it with pillows and blankets. Lots of pillows, lots of blankets, get in the bathtub, put the kids in the bathtub, get in on top of the kids.

NARRATOR: From Channel 9's command center, Gary and his viewers could see exactly what was coming.

GARY ENGLAND: Right now it may turn a little bit north of Norman. If it maintains itself, you folks in North...

TIM MARSHALL: May 3^rd, there was continuous coverage. They had helicopters up in the air filming the tornado, so people could watch the TV, see exactly where the tornado was. They had radar, with fantastic capability, showing the path that this thing was going to take. So people knew what was coming.

GARY ENGLAND: We've got it falling on the ground right now, right hand side, tornado on the ground right there. The green cloud, the green cloud, there it is.

After May 3, we had nearly 70 tornadoes in our viewing area, here in Oklahoma, and you know a lot of people killed, what, 8,000 structures destroyed? People pay attention now.

NARRATOR: The May 3^rd supertwister was the most powerful on record. And yet, after it finally fizzled out...

MAN: What's that right in front of us?

NARRATOR: Josh Wurman and his team discovered yet another supertwister roaring over open country.

JOSH WURMAN: During the May 3^rd outbreak there were at least 50 other tornadoes. One of those was over four times as large as the one that went through the metropolitan area of Oklahoma City. Had that tornado gone through Oklahoma City, it would have caused a damage swath four times as wide, probably a mile wide or more, destroying many times more structures than were actually destroyed.

TIM MARSHALL: The May 3^rd, '99 event is a major, major event to the people in Oklahoma and especially the people in Oklahoma City. But how many people outside that area realized what happened there? Realized the carnage that took place?

NARRATOR: It's not just powerful winds that make supertwisters so deadly. Once they form, they often keep on churning, staying on the ground an hour or more.

These so-called long-track supertwisters aren't confined to Tornado Alley. In 2002, one paid a sudden and unwelcome visit to a small town on the east coast.

MAN: It's coming this way, guys.

EMILY FERRIN: I remember seeing this huge funnel cloud, and it was holding things in the air that were just whirling so fast. And as they came to the top, you could recognize things like a tree, a couch, a desk.

MAN: You're expected, asked to take cover immediately.

SCOTT SCOFIELD: And we're looking at each other, thinking, "Is that a tornado? Where's it going?"

NARRATOR: It was a supertwister, sweeping straight through the center of La Plata, Maryland.

EMILY FERRIN: Then I remember this tangled mass of metal was coming right at me, I mean directly at my car. And briefly I thought, well, I'll probably get decapitated. And my car lifted two feet up in the air and actually moved under the CVS sign.

SCOTT SCOFIELD: Still I say it sounded like a jet turbine engine; I can't even duplicate the sound. And the house started rumbling, shaking.

NARRATOR: The giant vortex sped through town.

BARBARA WATSON: This tornado was moving at close to 60 miles an hour. That's a mile a minute. From here over to the buildings that are standing there, the tornado was probably through here in 15 seconds or less. One minute everything is there, and then, 15 seconds or less, everything is destroyed. It's amazing. You go from almost no wind up to 200 mile an hour wind and back down.

NARRATOR: As the tornado was ripping through downtown La Plata, just outside of town, Susan Erikson and her husband Erik were visiting the construction site of their new dream house.

They had no idea a tornado was coming.

SUSAN ERIKSON: The only thing we had heard on the news that day was thunderstorms. And we had thought, "No big deal."

We had just come up from the basement. I remember silence at that time, no birds, no anything. I just heard silence. And we were getting ready to leave, and then everything went blank.

NARRATOR: Susan came to in a pile of rubble, hearing the groans of her husband Erik.

SUSAN ERIKSON: Both my arms were broken, they weren't functioning correctly. So what I did was try to maneuver my legs, so that I could stand up and drag my arms up with me. I remember walking out of the house.

NARRATOR: Luckily, some neighbors found Susan before she passed out again. The next thing she knew, she was in the hospital.

SUSAN ERIKSON: It was between the two surgeries, before I went in for my orthopedic surgery on my arms, that they told me he had died. And they said he was in a morgue in Baltimore.

NARRATOR: Erik Erikson was one of five people killed by the supertwister that hit La Plata. Far from Tornado Alley, the monster storm carved a path of destruction 62 miles long, narrowly averting an unthinkable disaster.

TIM MARSHALL: If you were to have taken the La Plata, Maryland tornado and just moved it north about 30 or 40 miles, you would have gone from beltway to beltway, right across the Potomac and through the Nation's Capital.

NARRATOR: Rare as they are, supertwisters can strike anywhere, anytime. But no one knows why. In fact, scientists are stumped about what causes any tornado, large or small.

Unless they can solve the puzzle and figure out how a supercell thunderstorm creates a tornado, then predicting supertwisters will be impossible. But how do you decipher the inner workings of a tornado?

JOSH WURMAN: Meteorology, in contrast to chemistry or biology, is not a good laboratory science. We can't produce an accurate representation, a controlled representation of a thunderstorm, and change the variables one by one to make tornadoes.

NARRATOR: No one can create a real tornado, either on the plains or in a lab. But there is one place where scientists can play puppeteer with the weather: in a computer.

JOSH WURMAN: The closest approximations we have are computer simulations. And we try to build a digital, computational model of the tornado and see if we can change variables and have storms that produce tornadoes and ones that don't.

NARRATOR: One of the leaders in tornado computer modeling is Lou Wicker.

LOU WICKER (National Severe Storms Laboratory): It doesn't have good rotation. We're not going to deploy.

NARRATOR: 20 years ago, Lou was a young and eager storm chaser, tracking tornadoes the old-fashioned way, on the open plains.

LOU WICKER: We're moving west. A little farther, team, a little farther. Peak the hill, peak the hill.

NARRATOR: Back then, researchers thought the best way to learn about a tornado was to leave special sensors in its path. That was the idea behind Toto, a weather station the size of an oil drum.

Lou took charge of getting Toto as close as possible to a tornado without wiping out the research team.

LOU WICKER: In the '70s and the early '80s, we were just trying to understand what made storms work, sort of visually. Now we're moving into an area where we're trying to understand the dynamics of storms. Inside storms, dynamics means how the individual blobs of air are all interacting with each other to produce the flow that becomes either the strong winds, or even the tornado, or even the things that produce hail.

NARRATOR: Based on years of weather research, Lou produces an amazingly detailed computer simulation, designed with scientists at the University of Illinois. It reveals a familiar pattern: a thunderstorm explodes into the atmosphere, growing more intense every minute. The clouds begin to spin and roil high in the sky. They descend closer to the ground, still swirling rapidly. Suddenly, the rotation narrows and intensifies, and touches down to earth.

The question on everyone's mind is, "What triggers that final step? What makes the tornado form?"

JOSH WURMAN: Somehow, supercell thunderstorms are able to bring intense rotation and intensify that rotation near the surface. And we don't understand that process very well. We know that before a tornado forms, there are areas of rotation in the thunderstorm. What we don't understand is how that rotation is brought down to the ground and intensified in a very short period of time in order to make a tornado.

NARRATOR: In the search for a trigger, one of the primary suspects has been a burst of air descending from the storm, called a downdraft. The idea is that the downdraft wraps around the storm, tightening and intensifying the rotation.

LOU WICKER: We think the downdraft is really important for producing the tornado, because it would help sort of squeeze the air from near the ground up into the updraft. The air wraps around and sort of...the downdraft kind of comes around and squeezes the air in the front and the back together to kind of squirt the air up off the ground.

NARRATOR: In the minutes before a twister forms, storm chasers often see a downdraft blasting a hole in the clouds toward the rear of the storm.

JOSH WURMAN: Well, it's a very impressive storm. So far there's no tornado, but the structure looks quite good. We're seeing a very strong R.F.D. coming down. On the radar, it's still looking pretty good.

NARRATOR: But just as often, a tornado fails to materialize. There must be more to the story.

LOU WICKER: It's very likely that in order to solve the tornado problem, we're going to need a lot more data than we have right now, because a lot of things are going on at small scales that we don't actually sample. And so until we have that, it will remain a research problem.

NARRATOR: And so, every spring, storm chasers like Howie Bluestein hit the roads of Tornado Alley, all on the hunt for the tornado trigger.

HOWIE BLUESTEIN: What we want to do is capture the formation of tornadoes in many, many storms. We want to see precisely how the wind field is changing. We want to see what's happening to the temperature field and the humidity field for a lot of storms.

NARRATOR: Mobile Doppler radar is the key to mapping the swirling wind patterns that spawn tornadoes. Today's storm chasing teams often include at least two Doppler trucks so they can record the storm from multiple perspectives.

HOWIE BLUESTEIN: Twenty five years ago we went out by ourselves. Now when we go out, there's an armada of cars out there. There are a number of different mobile Doppler radars. And of course, the more vehicles you have out there, the more vehicles that need gas, the more people that have to run to the bathroom at bad times, and so on.

NARRATOR: All the high-tech sensors and computers they haul around allow Josh and Howie to monitor tornadoes in fantastic detail. The only problem is this equipment doesn't like to travel.

JOSH WURMAN: Radars, at some fundamental level, aren't really designed to be put on trucks and bounced around in severe storms. So we have a lot of problems with the complicated electronics, where things just shake and break apart. And we have shorts and things like that happening all the time.

We've broken our windshields now for the last two days. Our last one only lasted seven hours. That's pretty frustrating.

NARRATOR: When you're storm chasing, you have to be prepared for anything, whether it's treacherous road conditions, dust storms, or hail the size of baseballs.

MAN: That is a horse in front of us.

HERB: Oh, look at that.

MAN: Yes.

MAN: Oh, a horse. Well, of course.

MAN: Hey, hey, hey, hey, you guys running the truck...

NARRATOR: The messy and unpredictable reality of storm chasing shifts into high gear on May 15, 2003. Josh and Howie lead separate teams on the hunt for tornadoes.

HOWIE BLUESTEIN: May 15^th was incredibly complicated. We, and everyone else in the world, recognized that over the Texas panhandle the conditions were ripe for tornadic storms. The conditions looked very, very good.

NARRATOR: For a storm chaser, "very, very good" means lots of wind shear. Today, a zone of low pressure is drawing warm moist air from the south into the Texas panhandle. Just above it, the jet stream is blowing even faster. The two air masses, crossing at different speeds and altitudes, produce wind shear.

When there's wind shear, air near the ground begins to spin. If there's a thunderstorm in the area, it could take on this spin and perhaps go on to spawn a tornado.

As the chase begins, the team leaders must choose what part of the Texas panhandle looks most promising.

A lot is riding on the decision.

JOSH WURMAN: Well, we have a lot of anxiety, because it's a very high-stakes game. It's very expensive and time-consuming to go out after these storms, and they're fairly rare. So, we really need to make these calls efficiently if we're going to capture these rare events, and we only have a few chances every year to do that.

NARRATOR: Josh decides to head north toward Dalhart, Texas. Howie is unsure.

HOWIE BLUESTEIN: Now I can do my Lou Reed: "I don't know just where I'm going, but I'm going to try."

NARRATOR: His team needs to find an Internet connection to get an update on the weather. They find one in a restaurant in Shamrock, Texas.

HOWIE BLUESTEIN: Testing a 38 at Guadeloupe Pass. Oh, man! Oh, my god! Will you look at that! That is ridiculous. Look at the back winds, and they're strong. Oh, wow. It's going to be west of Amarillo. It's going to be...oh man, that looks juicy.

NARRATOR: Howie thinks the southern panhandle holds more promise. He also fears that up north, where Josh is headed, the road system is too sparse.

HOWIE BLUESTEIN: I'm not sure I want to get caught up in those storms in the northern Texas panhandle. They're going to go off into an area where the road network isn't too great.

NARRATOR: So Howie chooses to hang back near Amarillo, Texas, and wait for the storms to come to him. Having chosen the northern route, Josh lucks out. When the show begins, he's in perfect position.

MAN: There's the tornado. There's the tornado, looks nice.

JOSH WURMAN: Oh yeah, oh yeah! Looking at the radar, you'll be able to see that rotation pretty clearly.

We intercepted six tornadoes on that day. And one thing that was fascinating about that storm was there were at least two occasions where there were two vigorous tornadoes on the ground at the same time.

NARRATOR: This is the first time that twin tornadoes have ever been captured with ground-based mobile radar.

MAN: ...back to the southwest. I cannot miss you, ma'am.

JOSH WURMAN: Having two tornadoes in close proximity like that maintaining their vigor is very unusual. We've never seen that before in all our years of radar intercepts.

NARRATOR: Josh and his team take home the prize. They've captured high quality evidence on multiple tornadoes, including rare twin twisters.

In the meantime, about 100 miles to the south, the weather is depressingly fine, and Howie has captured nothing.

HOWIE BLUESTEIN: It doesn't like me, or she doesn't like me. It's the storm chaser's nightmare, to know that you made a good forecast in general, but there's a tornadic storm going on that you could have gotten that's just 100 miles away. You've driven all this great distance, made what you thought was a really good forecast, and you've missed a tornado by an hour or two hours. You feel terrible.

NARRATOR: After hours of waiting around the southern panhandle, watching the clouds on radar, things are looking bleak, when, finally, Howie gets an encouraging phone call.

HOWIE BLUESTEIN: Hello? Yes, Don. We are sitting in Hedley, right now, watching it on our radar—fantastic. That's what we've been watching. Okay, thanks a lot. Okay, I'm going to come out and look at it.

We have some good news.

Oh my God! Wow, hah, hah! Wow, that looks good. If the sun could go behind there, I could get a picture. That looks...that's really nice.

NARRATOR: What Howie sees is the vertical edge of a thunderstorm pushing up through the atmosphere and beginning to rotate, a supercell.

HOWIE BLUESTEIN: All of a sudden, one of the storms suddenly went up and became a supercell. It's as if someone had turned the switch on.

Looks like a good supercell. We're going to have to move here. We're having trouble with the computer.

NARRATOR: Even as the sun is setting, Howie's team tracks a series of storms back to the outskirts of Shamrock. Finally, a familiar pattern appears on the radar screen, a hook shape often associated with a strong, swirling downdraft and a tornado.

HOWIE BLUESTEIN: We have...the hook echo is just to our west, northwest, probably, right now, less than ten miles. It may be strengthening, and it may be another tornado, possibly. And we're collecting data right now.

NARRATOR: The Doppler radar reveals that just a few miles away a tornado is churning.

HOWIE BLUESTEIN: I hate to not be able to see it. If we didn't have the radar, we wouldn't be here. I've got to get back in. There's very, very strong inflow into the storm right now.

NARRATOR: It's extremely dangerous to be so close to a tornado, especially after dark.

HOWIE BLUESTEIN: We have a local sheriff...

If the storm had been moving at 35 miles per hour, coming right toward you, and you were near the storm, but you didn't know precisely where the storm was with respect to where you were, you could have been in great danger.

NARRATOR: Howie's eyes couldn't pierce the darkness to see the tornado, but his Doppler radar dish could. The radar kept Howie and his team safe, but did it capture any important clues to the tornado mystery?

To find out, Howie and Josh will both spend months, even years, back at their labs, dissecting the evidence they collected on this, the most productive day of the season.

The storm chasers will pack up their equipment in early June. But miles away, in the northern reaches of Tornado Alley, the show is far from over. And the stage is set for a rare appearance by the elusive supertwister.

The time is late June, 2003, and the place is South Dakota. There's no Doppler, no data and no theories. Instead, there are tornado tourists.

WOMAN: I think it's one of those things that...it's a force of nature that's so overwhelming you've got to experience it personally if you can.

WOMAN: I'm actually here hoping to see our first tornado. You know, we're not going right underneath these things. We're just hoping to see something, you know, from a distance.

ROGER HILL: Well, it's quite a volatile setup today for severe weather. We could even have a couple of very strong tornadoes today.

NARRATOR: Roger Hill directs a storm chasing tour company. He's not a scientist, but he does have a knack for finding tornadoes. His clients come for the adrenaline rush, to encounter nature in all its violent glory. They're seldom disappointed.

ROGER HILL: Folks, hang on. Hang on here. We're not slowing down. We're going to stick right up here with it. Oh, look at this. Look at this. Be careful, power lines are down here.

MAN: Power lines down. Power lines down.

ROGER HILL: Power lines are down.

MAN: Careful...

ROGER HILL: There's going to be a large tornado any time now.

MAN: Are we safe here?

ROGER HILL: Yes, you're safe right here. Oh, power lines are popping.

MAN: Get out.

ROGER HILL: Oh no, not now!

MAN: Large tornado! Large tornado! It's humongous. It's right west of us. We've got a great view of it.

MAN: Oh, man, look at it. Look at it!

MAN: Wow!

MAN: Look out, look out! Hang on, hang on! It's going 78 miles per hour. Hang on!

ROGER HILL: We've got a funnel. We have our next tornado developing.

NARRATOR: On June 24^th, Roger's group has a front row seat as a tornado sweeps by the town of Woonsocket, South Dakota.

ROGER HILL: Oh, a debris cloud has gotten out. It hit Woonsocket.

NARRATOR: The tornado dies out, but Roger knows there's more where that came from.

ROGER HILL: It's training dry air. It's going to go up and die. That one, up...though... we may need to head up that way, because that could be tornadic within the next 30, 45 minutes.

NARRATOR: They pile back in the vans to follow the storm as it regains its strength.

ROGER HILL: Stop right here, at these trees up here. Stop before these trees. Right here, right here. Here it comes. Here it comes.

MAN: It's forming into a wedge.

NARRATOR: A funnel cloud begins to take shape and then grows.

ROGER HILL: The condensation funnel's on its way down. Just keep videotaping.

NARRATOR: Suddenly, the tourists find themselves spectators to a terrifying display of nature's power: an F4 supertwister with winds over 200 miles per hour.

The tornado easily levels the town of Manchester. Fortunately, all six residents survived.

As the tornado continues across the plains, Roger and his excited entourage speed off to chase it. And the people of Manchester are left to pick up the pieces.

For those in its path, a supertwister like this is a nightmare. But for some scientists, this storm is a dream.

Back in Norman, Oklahoma, Lou Wicker decides to try to bring the Manchester supertwister back to life in digital form. Into a supercomputer go basic weather data—wind speeds, atmospheric pressure, humidity—all present before the tornado took shape. Then, the virtual storm grows on its own, and Lou sits back to see if a tornado actually forms.

The dynamics of the digital storm are rendered in incredible detail. Warm air, shown in orange, rises into the storm until it slams into the jet stream above. A column of air begins to spin rapidly. Sure enough, a tornado is born. A computer has succeeded in creating a tornado under the same basic conditions responsible for the real thing.

But what set the whole thing in motion? One of Lou's images shows a clear hook, and with it, a strong downdraft.

LOU WICKER: There's a very warm, moist air mass in this backside region here. And that's very interesting, because that means that while there is sort of a downdraft in there, it's not a cold rainy downdraft. It's sort of a warm, juicy downdraft, which will really help feed the storm.

NARRATOR: But in addition to the downdraft, Lou begins to discern a more subtle trigger for the tornado. To his surprise, the model reveals that just as the storm intensifies, a series of whirlwinds forms at ground level. These tiny corkscrews of wind merge together into a much larger vortex, the tornado itself.

LOU WICKER: It's very chaotic, and it's very complicated. It's not just a simple little downdraft here, and it just spins itself up. There are lots of things going on at the same time. I think it captures a lot of the complexity that we see in the real world.

NARRATOR: The whirlwinds that show up in the computer are so subtle, in real life they'd be invisible to the naked eye. But is there any evidence they exist in nature? Howie Bluestein believes there is.

HOWIE BLUESTEIN: We've been able to actually catch tornadoes in the act of forming, with very, very high resolution. And what you see is, well, it's not chaos, but you see a lot of small vortices. You don't see one vortex becoming a tornado, you see a number of small vortices.

NARRATOR: And the data proves it. Mini-twisters have shown up on both Howie's and Josh's radar before the tornado forms.

This adds a whole new layer of complexity in the tornado story. All the evidence is pointing to an amazingly intricate dance of wind and moisture interacting with the environment, including the terrain itself. The smallest changes can have a ripple effect in the atmosphere and can make the recipe just right for a tornado or even a supertwister.

The precise details are still being worked out, but Howie thinks we're closer than ever before.

HOWIE BLUESTEIN: I think that the solution may be in sight. We will, I think, within the next 10 years, with the mobile Doppler radars, actually see why tornadoes form.

NARRATOR: Everyone is painfully aware that lives are hanging in the balance.

HOWIE BLUESTEIN: We have been with tornadoes that have gone through towns and have killed people, and it makes you, it makes you feel sick. It's a horrible, horrible feeling.

But at the end of the day, we feel that, perhaps on the basis of what we've learned over a number of years, that we'll be able to eventually give people better warnings and hopefully save lives in the future.

JOSH WURMAN: If we can increase warning times by five or ten minutes, that's really significant. If we can push back the forecast of the tornado to 15 minutes before the tornado forms, people have 15 minutes to get to their shelters. So small increases of just 10 minutes, 15 minutes, 20 minutes, can have a great impact on the value of that forecast.

NARRATOR: With each season, the quest continues with a renewed sense of urgency. And every spring, when the supertwisters descend on the American heartland, sending residents fleeing for their lives, Howie and Josh will be driving toward the storm along familiar roads, hoping for a glimpse into the unknown.

JOSH WURMAN: It's the same kind of feeling that explorers probably had 300 years ago when they first saw a new mountain or a new river or a new continent. The modern day explorers are mostly scientific explorers. There are places in nature which have never been seen before or never understood before. So seeing inside a tornado for the first time, getting some understanding about how that tornado works, drives the explorer inside me to try to understand even more, to see even more tornadoes.

NARRATOR: Until they've unraveled the mystery of the tornado, storm chasers will continue to follow the clouds, probing ever deeper into the heart of the supertwister.