Original subtitles

NARRATOR: No winds in nature, are

more violent than the tornado.

They swirl up to 318 miles per hour,

packing a powerful 400-pound punch on every square foot

of exposed surface.

MAN: Major damage.

It's leveled entire buildings.

NARRATOR: And they can land without warning anywhere

they choose.

It was just pure devastation, like somebody just

dropped a bomb.

MAN: There are several thousand severe rotating thunderstorms

that occur in the United States every year,

but only about a quarter of them produce tornadoes.

And when we really don't know why.

MAN: Holy cow, you're looking at this thing, and it's--

it's getting ready move through your city, your town,

and affect your people.

NARRATOR: Earth, air, fire, and water,

essential for human survival, but in their extreme,

destructive to everything and everyone in their path.

MAN: Coming down right now.

Major tornado.

MAN: Damn, that's a monster.

NARRATOR: These are stories--

MAN: Oh, big time black.

MAN: Wow.

NARRATOR: --of Apocalypse Earth.

Among Mother Nature's disasters, tornadoes stand alone

as the most destructive form of severe weather on the planet,

and the United States has more of them

than any other country in the world.

Examining some of the most damaging tornadoes of the past

can help us prepare for the ones still to come.

On April 21, 1967, a killer tornado

touched down just 15 miles from Chicago's downtown loop

in the suburb of Oak Lawn.

It was the deadliest twister in Chicago history.

It barreled across the landscape at breakneck speed,

crossing through south Chicago in minutes.

It left the city stunned.

REPORTER: Tornadoes slash a 200-mile path

of death and destruction across northern Illinois.

Stunned residents try to salvage their belongings.

The vicious twister struck without warning.

It was a landmark event for Chicago.

It is a baseline to which other people compare

future tornadoes.

NARRATOR: While experienced forecasters knew twisters could

happen in Chicago, nothing had quite prepared them

for the violence of this event.

I was a little panicked myself, personally,

and very much aware of how bad things were.

NARRATOR: And the Oak Lawn tornado

was only one of 52 twisters to hit the region that day.

Henry Yario was a meteorologist on duty the day

it all went down.

This was what we call a family outbreak.

A family outbreak means there will be many tornadoes.

NARRATOR: And a major outbreak, with tornadoes striking

in a broad band covering five states from Iowa to Michigan.

17 of the 52 twisters touched down

within 125 miles of Chicago.

Family outbreaks this big occur only five to six times

a century.

I was 11 years old at the time of the Oak Lawn tornado,

and I remember that day very vividly.

NARRATOR: Tim Marshall grew up in the Chicago suburb of Oak

Lawn, and the tornado inspired his career

in meteorology and engineering.

When as an adult, he saw the weather map from that day,

he was shocked.

When I looked at the April 21, 1967 weather map,

I said in the great words of Harry Carey, holy cow.

It had all of the ingredients that are needed

for a major tornado day.

NARRATOR: Here's what alarmed forecasters on that day.

The rotation of two low pressure centers

was driving warm, moist air up from the Gulf of Mexico

with a warm front showing the leading edge of the air mass.

Next, a cold front marked where a mass of frigid air

was clashing with the Gulf air.

The massive cold front punched under the warm air,

quickly shooting it up to higher altitudes.

This fast rising warm air smashed

into the upper atmosphere, where temperatures

were super cold, minus 15 degrees Celsius at 18,000 feet.

The instability of cold air above warm created storms.

Shifting winds added rotation to the storms, which enabled them

to last for hours and gave them the capacity to form tornadoes.

These storm systems are called super cells, a term that

was coined in 1964, only three years after the outbreak.

In 1967, the National Severe Storms Forecast Center

in Kansas City had responsibility

for monitoring the nation's weather for tornadoes.

At 1:00 PM, forecasters sent out an alert via teletype

based on the alarming weather map of the day.

It was a tornado watch.

It was issued for that afternoon,

and it included all of northern Illinois, southeast Wisconsin.

It went over into lower Michigan.

NARRATOR: Local forecasters in Chicago

kept their eyes and ears open for tornadoes.

They depended heavily on calls from ground spotters

to identify twisters.

Weather satellite technology was still in its infancy,

and radar technology was relatively primitive as well.

Its use in weather forecasting dated from 1948, when the Air

Force conducted the Thunderstorm Project to study severe storms.

Even two decades later, the radar gear then available

showed only the vague outlines of the coming storms.

Back in the old days, we call it,

wasn't much in the way of radar to really see through a storm.

More or less, these echoes appear like blobs,

and it was very difficult to detect these tornadoes.

NARRATOR: At 3:40 PM, weather spotters on the ground

sighted the first in the day's family outbreak.

But it was too late to save the people in the twister's path.

The tornado struck with a vengeance in Belvidere,

Illinois, 73 miles northwest of downtown Chicago,

with damaging winds speeds up to 260 miles per hour.

It leveled houses and tore structures

from their foundations.

Hardest hit was Belvidere High School, where students

were boarding buses to go home.

13 children died here, and 11 other people

were killed as the twister remained on the ground

for half an hour.

Debris was everywhere, including a marriage certificate lofted

97 miles away to Milwaukee.

Tornadoes have been known to hurl paper items as far as 305

miles.

The Belvidere twister scoured a 25-mile path all the way

to Woodstock, Illinois.

At 5:00 PM, a second tornado ran 9 miles from Fox River Grove

to Lake Zurich.

24 minutes later, the day's worst twister

struck 4 miles west of Oak Lawn, beginning its incredible race

across Chicago's southern suburbs.

People living in Chicago should take tornadoes

seriously, because it can happen, and I'm living proof.

NARRATOR: Skip Sullivan is a coach at Oak Lawn High School.

On the day of the tornado, he was a student there.

He was at school watching a track meet at 5:30 when he went

inside to get away from approaching rain clouds.

The golf team came running in screaming, get back,

there's a tornado.

There's a tornado.

The lights went off, and all-- all I can recall doing

is I turned around, I started to run,

and I immediately hit the floor.

Within seconds, it was all over.

NARRATOR: On April 21, 1967, a killer tornado touched down

just 15 miles from Chicago's downtown loop

in the suburb of Oak Lawn.

It was the deadliest twister in Chicago history.

SKIP SULLIVAN: The lights went off,

and all-- all I can recall doing is I turned around, I started

to run and I immediately hit the floor.

Within seconds, it was all over.

The whole front end of the school was ripped off.

The pool had collapsed.

And it was just like they dropped a bomb here.

NARRATOR: On the wall above the wrecked swimming

pool was a clock frozen at the time the tornado hit, 5:31 PM,

rush hour.

Tornadoes don't strike at convenient times.

They strike when they're gonna strike.

Could be middle of rush hour where they're in their cars,

and they heard the warning that it's coming,

but where am I gonna go?

NARRATOR: The tornado did the greatest damage

just next to the high school at one of Oak Lawn's busiest

intersections, Southwest Highway and 95th Street.

40 cars stopped at traffic lights, their drivers helpless.

17 people were killed right here.

Only one photo of the actual tornado

itself is known to exist.

It clearly shows the parent storm's

characteristic super cell wall cloud

caused by lowered pressure in the area surrounding

the tornado.

Oak Lawn residents also took hundreds of other photos,

recording the massive damage left behind.

The scenes they preserve are bizarre.

Among the most memorable, a local transit

station where rows of buses became an instant junkyard.

These were old, very heavy buses.

And to see them crumpled up like a beer can and tossed around,

I mean, that's just amazing to me.

We try to rationally explain something

that appears irrational.

And usually, we are pretty good at it,

but there are some things that defy explanation.

One of the photographs in Oak Lawn

was of a picture or photo album that was embedded in a tree.

That tells you that when you have an object that's

fairly small moving at a high velocity,

it can go through things like wood.

There is a dimer that is completely destroyed,

except the front door and the clear story window above it

are all intact.

The glass is intact.

Now, that's amazing to me.

NARRATOR: Even more amazing is the speed of it all.

The twister tore through Oak Lawn in only five minutes,

with a damage path maxing out at 600 feet wide.

Its path of destruction tore across the southwest suburbs

and ran all the way through south Chicago

to the shores of Lake Michigan.

But it could have been much worse.

Ahead was suburban Chicago's entire south side,

defenseless against a mega disaster.

Reports of tornado destruction and survival in suburban areas

like Oak Lawn can be intense, but so can the stories

of survivors of twisters in more rural parts

of the central plains.

[music playing]

Tushka, Oklahoma.

Until 1907, this part of the American heartland

was controlled by the Choctaw Indians,

but it's always been at the mercy of mother nature.

This area has more tornadoes than any other place

on the planet.

And the reason is that it's right at the intersection

between big cold air masses in the north

and warm, moist air masses that come up

from the Gulf of Mexico.

When these air masses intersect, they spawn giant thunderstorms,

and these huge thunderstorms are the perfect breeding grounds

for tornadoes.

[music playing]

NARRATOR: Outside of Tushka, amateur storm chasers

watch a monster taking shape.

April, 2011 will go down in history

as one of the most destructive and deadly seasons

for tornadoes.

Between April 14 and the 16th, there was a strong area

of low pressure that went through the central plains

and then went into the south, and over a three-day period,

there were over 300 tornadoes.

This was an enormous tornado outbreak.

This tornado was confirmed as an EF3 tornado.

It was 165 mile per hour winds.

This was a very violent tornado.

It stayed on the ground for a 15-mile long path.

NARRATOR: It's now the storm doing the chasing.

NARRATOR: They're not the only motorists

trying to escape the twister's wrath.

So were Jason and Desiree Miller and their two kids

who have fled their home upon hearing tornado sirens.

We decided to seek shelter at the Tushka schools,

because that was the only one we knew of at the time.

NARRATOR: The family speeds into the parking lot,

thinking they'll find safety inside the school.

But there is one major problem.

The time we did get to the door, it was locked.

There was already people leaning on the doors,

because if they were to open those doors and let us in,

it would have been a vacuum effect.

It would have sucked everybody else out.

NARRATOR: Now, the family is stuck

outside as the giant twister suddenly bears down on them.

I ran over to the fence as it was next to a brick wall,

and it was the only thing I could find to hold onto.

I held on to the fence and I was yelling at her to come over,

and she started coming toward me, so I reached, grabbed her,

and we both huddled and sandwiched our kids between us.

NARRATOR: The family is locked in a brutal tug of war

with mother nature.

They fight to maintain their grip, knowing

that one slip could be deadly.

I had my hands on both the kids.

He's screaming, look down, look down, don't look up.

He's watching the school building being ripped apart.

NARRATOR: In the midst of the cyclonic fury,

the winds bring another surprise attack,

using a 2-ton lethal weapon.

Normally, in a tornado, we would

expect to see a vehicle rocking back and forth as it's buffeted

by the winds.

And what I think is going on there

is the tornado provides a bit of uplift, perhaps an air cushion

under the vehicle that allows the horizontal forces

of a tornado to move it gently sideways.

NARRATOR: One more move from the SUV

could crush the family in an instant.

That is, if they survived the brutal onslaught.

When you have wind speeds of over 165 miles per hour,

you have flying debris, bricks, glass, nails.

It can put out your sight.

It can easily kill you.

NARRATOR: Against all odds, the Millers

manage to cling to the rail, fighting to keep from getting

blown sky high.

Nine minutes we squatted there,

being hit with everything you can possibly imagine.

We didn't think we were coming home.

There was no way.

We thought it was the end.

NARRATOR: Finally, after what seems like an eternity,

the ferocious gale dissipates.

All of a sudden, it just stopped,

like it had never happened.

All the winds died, all the debris stopped,

everything stopped moving, and it was calm.

NARRATOR: Aside from minor scrapes and bruises,

the Millers have somehow lived through this horrific

nightmare.

I can't believe that we're walking away from this.

I can't believe we're all still here.

The chances of that are astronomical.

NARRATOR: As the storm moves away from Tushka,

residents are stunned by the destruction the twister leaves

in its wake.

MAN: Oh, no, look at that semi.

Oh, no.

[dramatic music]

If you thought that tornadoes only hit rural areas,

it's time for a fact check.

MAN: That's a house. MAN: Oh, my god!

MAN: Oh, no!

NARRATOR: Any place is vulnerable to tornadoes,

including cities, especially those in America's midsection,

where twisters occur more often than any place on Earth.

If you wait long enough probably

every major city in the central part of the country

is going to have a tornado hit the downtown.

NARRATOR: Consider St. Louis, Dallas, Oklahoma City.

None of them is safe.

The biggest target in the region is Chicago, the nation's

third largest city, where a devastating tornado struck

in 1967, proving it could happen again.

On that day, April 21, bizarre weather conditions

produced a massive family outbreak,

sending 52 tornadoes across Illinois and four other states.

The most severe twister of the day

sped through the Chicago suburb of Oak Lawn.

Most of Chicago's three and 1/2 million residents

were caught by surprise.

We never talked about there's tornado warnings or tornado

watches.

So we never had that in our thoughts

that we better watch where we're at.

NARRATOR: After the twister tore its deadly path through Oak

Lawn, it raced across Chicago's southern suburbs

at breakneck speed.

[dramatic music]

In the space of six minutes, it continued through the Chicago

neighborhoods of Hometown and Evergreen Park.

It uprooted trees, and toppled headstones in a cemetery,

damaged a steel plant, destroyed chimneys, and blew out windows

all along its path.

The tornado crossed the Dan Ryan Expressway, clipping

a semi-trailer, and went on through South Chicago

before leaving the city at the shores of Lake Michigan.

It went out across the lake as a waterspout, the term

given to any tornado over water.

With no observers to track it, we'll

never know how long it lasted.

Here is another myth, that lakes are cold water

and, therefore, tornadoes don't like cold water,

and they won't form over them or go over them.

That's nonsense.

The tornado is a byproduct of a very warm thunderstorm.

It's not going to care about a lake.

[dramatic music]

NARRATOR: The Oak Lawn Tornado scoured a 16.2-mile path,

killing 33 people, and injuring another thousand.

$50 million worth of property was destroyed--

$391 million in today's dollars.

[indistinct shouting]

A tornado's intensity is now measured

by looking at its damage and rating on the F scale,

from F0 to F5.

But the F scale did not exist in 1967.

[dramatic music]

It was not developed until 1971 by University of Chicago

professor Ted Fujita.

So engineers estimate the Oak Lawn Tornado's intensity

from damage photos.

This powerful tornado was certainly at the upper level

of the F Scale.

Some say it was an F4, others an F5.

But an expert eye can tell the difference.

In terms of housing, here's how the F scale works.

F0 is loss of some shingles and some things like antennas,

chimneys.

With F1, you're going to be losing part of the roof.

We're talking about some decking.

With F2, you lose the entire roof.

With F3, you're losing the roof and exterior walls.

With F4, only the center walls are remaining standing.

And at an F5, it's completely gone.

NARRATOR: At 65-miles an hour, the F4 tornado's ground speed

was more than twice that of the average twister,

and just seven miles per hour below the record.

[dramatic music]

The fastest on record was 1925's Tri-State Tornado

at 72-miles per hour.

Its path was 219 miles, lasted three and 1/2 hours,

and killed 695 people--

the deadliest tornado in history.

The Tri-State Tornado was part of a small family outbreak

of six different tornadoes.

The Oak Lawn twisters outbreak was much larger,

with 52 twisters--

a frightening number.

History, however, has shown us things can be even more

extreme.

Family outbreaks occur over wide areas,

sometimes covering a dozen or more states on the same day.

Some family outbreaks result from multiple tornadoes

generated by a single supercell thunderstorm

as it travels across the terrain.

Others come from widespread weather conditions that

simultaneously produce many supercells,

all capable of sending down tornadoes.

Any more than 20 tornadoes is considered a large outbreak.

MAN: Holy-- my god!

MAN: That is incredible.

NARRATOR: The largest of all time

is known as the Super Outbreak of April 3, 1974--

148 tornadoes swarming across 13 states in 18 hours.

Among the twisters in this devastating event,

six were F5s and 24 were F4s, record numbers

for a single outbreak.

Most occurred in Indiana, Ohio, Kentucky, and Tennessee.

But tornadoes were cited as far north as New York state.

Worst hit in the super outbreak was the city

of Xenia in southwest Ohio.

An F5 tornado killed 32 people, injured more than a thousand,

and leveled a quarter of the city.

When it was all over, the 148 tornadoes

had left behind trails of destruction

nearly 2,600 miles long, killing 315 people,

and causing $600 million in damage--

the equivalent today of more than $3 and 1/2 billion.

[wind roaring]

Due to limitations, such as lack of damage indicators,

in February of 2007, the Fujita scale

was revised to the Enhanced Fujita Scale.

Developed by a forum of nationally-renowned

meteorologists and engineers, the EF Scale

gives a more accurate definition of tornadoes

by aligning wind speeds more closely with storm damage.

It incorporates 28 damage indicators, such as building

type, structures, and trees.

The National Weather Service is the only federal agency

with the authority to provide official tornado EF Scale

ratings.

[wind roaring]

The science of tcalled fiendish.

And to understand these terrifying storms,

we not only have to observe them in the field,

we have to go into the lab and actually create them.

Here at Iowa State University, the man-made tornado

may give us new insights into one of nature's most

violent phenomena.

[dramatic music]

A team of scientists has developed an amazing instrument

that puts the city of Chicago to the tornado

test inside the laboratory.

Partha Sarkar heads the experiment.

Well, we have seen the tornado moving through downtown Chicago

in around Sears Tower.

And we are seeing the vortex, actually, as it is circulating,

and a lot of debris field flying around--

what will typically happen in a real tornado.

All right. Because--

NARRATOR: Sarkar and his colleagues

are utilizing the nation's largest tornado simulator.

Built in 2004, the machine is 18-feet across, 11-feet high,

and is suspended from a five ton crane.

[whoosh]

Dry ice at minus 109 degrees is used to make the swirling

vortex visible.

I think of tornadoes as the final frontier, in some ways,

with regard to meteorology because we still don't know

exactly what creates a tornado at the ground.

NARRATOR: This extraordinary machine

may help solve the mystery.

The way it produces tornadoes in the lab

is the same way some scientists believe it happens in nature.

[dramatic music]

Here's how it works.

A central fan creates an updraft.

At the top, the air flows through a set of veins, which

give it some rotation, as it then circulates to form

a donut-shaped downdraft.

At the bottom, a swirling vortex forms, the laboratory tornado.

Real tornadoes, some say, are formed by similar downdrafts.

Maybe only 10% or 20% of spinning storms

actually produce a tornado at the ground.

And we don't fully understand why that is.

NARRATOR: In supercell thunderstorms,

these bursts of air crashing to the surface

are called "rear flanking downdrafts."

They aren't always donut-shaped.

But when they are, as in the simulator,

the storm will produce a tornado.

I think the fact that this simulator is able to create

a tornado so easily based on this theory

suggests that it's very likely that many of our tornadoes

do come about from this process.

NARRATOR: The simulator enables researchers to study how

tornadoes form without exposing them to the risk of gathering

data during actual storms.

But the primary mission of the simulator

is to discover what tornado winds do when they strike

buildings--

the kinds of buildings that crowd the cityscape of Chicago.

By building a simulator like this,

we can reproduce the effects of a tornado hitting downtown

Chicago every hour if we want.

NARRATOR: Sensors in the model's structures

read the wind forces acting on them.

The data is crucial information for engineers

who work on skyscrapers.

When you're designing a tall building,

you need to account for how much force the wind is going

to exert on your building.

You have to know what that is so that you can design

the building to be strong enough.

So what we have built here is a simulator

that gives us a tornado that can interact with a building.

And we can see how much force the tornado is going

to exert on it.

NARRATOR: The machine is the only simulator that actually

moves its tornado across the terrain,

as twisters do in nature.

MAN: Back up!

Back up!

NARRATOR: Although many small buildings have been tested

until now, this is the first day of simulation with a scale

model Chicago.

It's the largest test so far.

Ready to go?

NARRATOR: The scientists have taken great pains

to make sure their scaled down twister is an accurate

representation of the real thing.

The way that we test whether or not

we have a good simulation is we've been comparing

our results with radar data, the people that take

radar data of real tornadoes.

And the comparisons are very, very good.

And what we then do is we scale our building models

to an appropriate size relative to that tornado.

NARRATOR: The Chicago simulation shows

a major tornado nearly 1,200 yards wide

hitting the city center--

big buildings versus a big tornado.

When we think of a big building,

it's big compared to us.

But compared to storms that could be 30,000 or 40,000-feet

tall, it really is not that big.

And so the tornado is going to come through the city

whether the buildings are there or not.

NARRATOR: The simulator dramatically proves why cities

are not immune to tornadoes.

The man-made twister is totally undisturbed

as it slices past the massive skyscrapers.

In real life, the terrible winds would smash the buildings

to pieces.

Out in the city itself, hundreds of skyscrapers

crowd the streets around the loop.

Despite the potential for destruction,

engineers say tornadoes are not even a factor in the designs

for Chicago's high-rises.

Engineering is all about probabilities.

And the probability of a tornado hitting a particular spot

is so small that we really don't consider it explicitly

in the design.

NARRATOR: Skyscrapers are designed for high winds

though, the 90-mile per hour gusts that occur on average

once every 50 years.

[wind roaring]

But 90-miles per hour pales in comparison

to the 250-mile per hour winds of a tornado.

Most tall buildings get their strength from steel frames.

76,000 tons of steel were used in the 1,450-foot former Sears

Tower, Chicago's tallest building.

And hundreds of other structures employ the same material.

Steel is really the mode of choice for me

in terms of a structure that can withstand those high forces.

It can take a tremendous amount of impact, a tremendous amount

of wind.

So I'm not concerned about how steel will react in a tornado.

I know that it's going to stay there.

NARRATOR: Today, many modern high-rises

are constructed with steel-reinforced concrete

rather than all-steel frames.

Concrete skyscrapers are embedded with super strength

rebar, making the overall building as strong

as steel in resisting wind.

But, whether steel or concrete, structural strength

may not be enough when tornadoes strike skyscrapers.

[wind roaring]

[dramatic music]

NARRATOR: In 2000, an F2 tornado went right through downtown

Fort Worth, Texas.

MAN: Downtown Fort Worth right there.

And then the tornado is just to my south there.

NARRATOR: Hardest hit was the 37-story Bank One Tower.

It's $40 million in damage was more than it was worth,

and it remained vacant for two years.

You wouldn't actually see a skyscraper collapse in most

cases from a tornado strike.

But the damage that would be done would be nearly total.

It would be very similar to what would happen if the structure

had actually collapsed.

People who think a city might somehow stop a tornado

only have to look at what happened in Nashville

or what happened in Fort Worth, and see that the tornado didn't

really seem to care a whole lot that it was having to trudge

through all these big buildings.

NARRATOR: Nashville and Fort Worth

are just two examples of city tornadoes on the record books.

Downtowns were also struck in Miami and Houston.

Even a place far outside Tornado Alley, like Salt Lake City,

is not immune.

There, on August 11, 1999, a surprise tornado

went right through downtown.

From the air, it looks as though someone whose plowed

a furrow directly on a line of almost surgical proportion.

The randomness of it is startling.

NARRATOR: The Salt Lake City twister proves that tornadoes

can strike anywhere.

This one happened in a state that experiences only two

tornadoes a year.

[whoosh]

The 150-mile per hour twister damaged large buildings,

such as the arena where the Utah Jazz play.

But it was devastating for weaker structures,

like this tent, housing a trade show.

Most of the 100-plus injuries happened here.

One person was killed.

And, as in any tornado, there was the bizarre.

This power pole seems normal at first glance,

until you see it is hanging from its own wires, snapped away

from its lower half.

And imagine finding a piece of a tree jammed into your car's

engine compartment.

You can see it's gone right through it, right

into it, right through it.

The whole tree, it went right through, took the radiator,

and went right through the battery.

Well, it's undriveable now.

NARRATOR: And the history of tornadoes and cities

goes back much farther.

In 1896, St. Louis was devastated

by a monstrous mega twister, the kind of event that

ranks with the San Francisco earthquake in the annals

of disasters.

Known as the "Cyclone of 1896," it's the deadliest event

in St. Louis history.

At least 255 people were killed.

8,800 buildings were damaged.

Its economic impact equivalent to a $4 billion disaster today.

A haunting image from that time shows a common shovel jammed

six full inches into the dense trunk of a fallen tree,

a testament to the power of tornado winds.

The power of a tornado is so strong

that airports built to withstand intense wind gusts

are also vulnerable to Mother Nature's fury,

as evidenced in recent tornadoes in St. Louis.

[dramatic music]

St. Louis, Missouri, located in the outskirts of Tornado Alley,

this city sees its share of harsh weather.

But a thunderstorm on the horizon has this city on edge.

This supercell thunderstorm is capable of producing

severe winds, damaging hail, and possible tornadoes.

Tornado warning is in effect.

A tornado warning means that a tornado is either on the ground

or it's imminent.

It's very likely, the conditions are ripe.

In the early evening, residents

wonder where a tornado will strike.

The National Weather Service provided 34-minutes of warning

that tornadoes were coming.

The emergency alert people set the sirens going.

And all the TV stations dropped their regular program

and were showing the radar images of the storm coming

this way.

NARRATOR: Inside Lambert-St. Louis International Airport,

travelers are oblivious to the imminent threat.

I think most people feel safe at an airport.

And you can see these people.

They look calm, cool.

They're on their cellphones.

They're texting.

They're just sitting there.

NARRATOR: But unusual cloudbursts outside the window

give passenger John Avaro a feeling of dread.

There's rain coming down like I've never seen in my life.

And it's a wall.

It's not coming down direct.

It's-- it's going sideways.

At that point, you're starting to get antsy.

Something's up.

Something is up here.

[LIGHTNING STRIKES AND THUNDER CLAPS]

NARRATOR: Suddenly, John gets proof of just how strong

the winds are.

This plane was there.

And it was moving back and forth.

It was shifting.

All of a sudden, the plane shifted 50 feet

and it tore away, just by the sudden gust of the wind.

At that point, yeah, I was worried, big time.

If you think about an airplane, how they're designed,

they're designed to take advantage of wind.

They're looking for uplift.

Well, when a tornado comes through, Earth's most violent

windstorm, it's going to treat them like they're little toys.

[dramatic music]

NARRATOR: An EF4 tornado begins to tear a path of destruction

towards Lambert Field.

NARRATOR: Shielded by darkness and the soundproof glass

in the main terminal, George Merriam and his friend

Adam Loughton are unaware of the monster bearing down on them.

MAN: Wow, I just saw that hit.

Boredom has seriously set in.

Adam is videotaping, and I'm texting,

saying the flight is delayed.

It doesn't look like we're going to make it.

Sound is one of the warning signs

that we have of an approaching tornado.

With an airport terminal, that sound

would be greatly deadened.

[indistinct chatter]

NARRATOR: They may not be able to see or hear a tornado,

but they're beginning to feel it.

[people exclaiming in alarm]

The windows in this terminal would have been designed

for wind speeds of perhaps 100-miles an hour.

The winds associated with tornado,

we're looking at four to eight times the amount of force

on the glass.

NARRATOR: The passengers start to realize the full power

of the danger that lies just outside.

These giant windows were flexing from the change

in pressure to a point where they couldn't hold

their structure and gave way.

NARRATOR: In an instant, panic explodes

in the terminal as the twister blasts

through the tempered glass.

All of a sudden it was, "You've got to go.

Run!"

[people screaming]

I turned around to my wife, and I said, "Honey, we have to go.

Come on.

Let's go now."

MAN: Come on.

[people screaming]

NARRATOR: 165-mile an hour winds roar through the building.

It happened so fast.

This is a tornado.

This building could possibly leave its current location,

and we're all going to go with it.

NARRATOR: In every concourse, passengers and crew members

run for their lives.

This tornado hits the terminal very quickly.

[shattering]

The shattering of the windows now opens up

the inside of the terminal to tornadic winds

coming through the terminal.

One of the biggest dangers in tornadoes

is those winds picking up debris and hurling them,

like missiles.

NARRATOR: The winds hurled trash cans, signs, and vending

machines through the building.

In the main terminal, George reels from the full force

of the blast.

MAN: Holy shit.

It was chaos, and explosion, and falling debris.

All the ticket booths were gone.

All of the shops were destroyed.

Everything was in total chaos.

George, you all right?

This airport has just been blown up.

NARRATOR: The dazed and shaken passengers don't

know if the threat has passed.

MAN: I would probably get away from that plane

'cause it's venting fuel.

MAN: I don't want to be here.

It's not a smart thing to do to sit under the middle

of a big, wide-span roof with a tornado.

Once the wind breaks through the plate glass windows,

the pressure to help lift the entire roof off is great.

You want to get into those hallways.

Walls close to each other, narrow space,

that's the best protection place to be in during that tornado.

NARRATOR: Quick-thinking airport personnel moved everyone down

to the basement.

None of us had any idea how bad it was.

And then people started coming in

and they were covered in blood.

NARRATOR: As terrified travelers struggled to make sense of what

just happened, Mother Nature continues to wreak havoc

in the terminal above.

[whoosh]

[dramatic music]

When the tornado has left the scene,

emergency crews move in to assess the damage.

[dramatic music]

Though the destruction to the building is extensive,

this time, the tornado misses a chance to exact a human toll.

Several things could have been worse about this.

The EF4 has slowed down by the time it got to the airport.

It was in the EF3 category.

[whoosh, shattering]

Had that been EF4, I think we'd have seen far more damage.

This was a significant tornado.

[people screaming]

It is stunning, with all the damage that you see,

that there weren't more injuries or some deaths in this.

That's stunning.

LIGHTNING CRACKLES, THUNDER RUMBLES]

NARRATOR: One of the most powerful tornadoes in history

slammed into Oklahoma City on May 3, 1999, only one

of 70 tornadoes in a massive outbreak.

[wind roaring]

For 85 agonizing minutes, it scours a path estimated at one

mile wide and 38-miles long.

[lightning crackles]

As far as I'm concerned, the tornado event of May 3, 1999

was the most significant tornadic event

I have ever seen, and have ever witnessed,

or even seen pictures of.

[dramatic music]

NARRATOR: The storms producing the Oklahoma City Tornado

started around 4 PM.

Late afternoon is prime tornado time,

when the heat of the long day accumulates in the atmosphere.

Heat is the driving force in a thunderstorm.

Hot air rises, creates motion in the air.

Motion becomes wind.

And if there's enough wind, the end result can be tornadoes.

MAN: Very large tornado.

[dramatic music]

NARRATOR: That day, Gary England,

weathercaster for Oklahoma City's channel 9,

gave his first reported 4 PM.

It's still fine.

A little windy on the north end, OK.

It was like many, many other days.

Conditions were favorable, it looked like,

during the afternoon, and evening, and night,

for tornadic activity.

But it looked like so many other days.

We've seen this situation hundreds, if not thousands,

of times in the last 30 years.

NARRATOR: Oklahoma City is in Tornado Alley, a popular term

for a band of high risk areas running from Texas to North

Dakota.

[dramatic music]

It's where conditions combine most often to produce

supercell thunderstorms.

A supercell is essentially a rotating thunderstorm.

It's rotating about a vertical axis.

It looks like a bathtub vortex, if you will.

NARRATOR: Cross currents of air start the process,

setting up a horizontal rotation in the atmosphere.

Then warm, moist air from the Gulf of Mexico

rises up, forcing the rotation into a vertical position.

Cold air from Canada clashes with the warm, which rises,

making its moisture condense into rain.

And the storm's spin intensifies the whole process.

But, amazingly, just how this rotation

turns into the violent vortex we call

the tornado remains a mystery.

There are several thousand severe, rotating thunderstorms

that occur in the United States every year.

But only about a quarter of them produce tornadoes.

And we really don't know why.

NARRATOR: That day in Oklahoma City, forecasters watched

the supercells carefully, using Doppler radar, the primary tool

for seeing inside the circling storms.

[dramatic music]

But the giant radar domes of the National Weather Service

have their limitations.

Locked in fixed positions, they usually

see storms only at a distance.

And a scan with each full rotation takes six minutes--

an eternity in the fast-moving world of tornadoes.

MAN: What is that?

Only the human eye can confirm a twister's contact

with the ground.

Tornado chasers see the first at 4:30 PM.

And for the next 11 hours, one tornado after another

strikes the landscape.

MAN: Yes, it's coming down right now.

Major tornado.

We have a large tornado on the ground.

This is tornado number six or something.

NARRATOR: As the tornadoes come down,

Professor Josh Wurman is on the road,

chasing the twister with his mobile radar truck, Doppler

on Wheels.

Unlike fixed radar towers, this Doppler

can go anywhere, anytime to confront a tornado

face-to-face.

Wurman hopes his research will result in better tornado

forecasting for the future.

We're trying to observe tornadoes from close up.

And that means we need to be exactly where the tornadoes

are.

NARRATOR: The chasers target the trailing edge of the storm.

Strong, high level winds blow the rain miles away,

to the front of the supercell.

Most of the real action is at the rear of the storm, where

the high speed updraft sucks air in.

[whoosh]

Here is where the rotation is strongest.

This is tornado country.

Another scientist on the chase is Chuck Doswell.

He's a meteorologist at the National Severe Storms

Laboratory.

CHUCK DOSWELL: I've been chasing for 30 years.

And I knew right away that it was something very dramatic.

I'm just north of Chickasha on the interstate.

What a storm!

[dramatic music]

NARRATOR: Chickasha is 40 miles southwest of Oklahoma City.

The tornado here is rated at F2.

CHUCK DOSWELL: Two miles west of-- west of Chickasha.

NARRATOR: It lasts nine minutes, unusual for a tornado.

Most of them fizzle after a minute or two.

MAN: 2343--

NARRATOR: And another more powerful tornado touches

down moments later.

MAN: OK, go.

It's not leveling.

NARRATOR: The dark massive wind immediately

dominates the landscape.

MAN: Yeah, we are.

NARRATOR: Every one of the chasers

who pursues it is astounded.

For Chuck Doswell, the danger is clear.

CHUCK DOSWELL: I'll tell you what, Oklahoma City is

about to get hammered.

[whoosh]

NARRATOR: Now, the most destructive tornado in history

is barreling down the highway.

And Oklahoma City is dead ahead.

MAN: Yeah, I hope this doesn't go to Oklahoma City.

It's going to be strong.

During the late afternoon and evening hours

on May 3, 1999, multiple thunderstorms

produced many large and damaging tornadoes in central Oklahoma.

MAN: Oh, my gosh!

WOMAN: Oh, my gosh!

[dramatic music]

MAN: Got a major tornado.

MAN: It's coming down right now.

NARRATOR: By 6:20, 11 tornadoes have already hit.

But now, a monster comes crashing down.

MAN: Huge.

[lightning crackles]

[dramatic music]

NARRATOR: It is the 100th tornado

to hit Oklahoma City in a century of record-keeping.

It's the biggest one of all.

It was an emotional roller coaster.

You know, it was obviously this thing was going to kill people.

And there was nothing we could do about it except

warn the people.

NARRATOR: Experienced chasers describe tornadoes

by their shapes--

a stovepipe tornado, stout with straight sides;

a rope tornado, slender and sinuous,

usually taking this form in its late stages.

But this tornado in Oklahoma City

is called a "wedge," wider than it is tall.

This shape, with more contact with the ground,

tends to be more destructive.

And this wedge is enormous, up to a mile wide.

MAN: That is a great big wedge.

CHUCK DOSWELL: It went into that wedge mode.

And it stayed in that mode for at least 20 to 30 minutes.

I've never seen a storm do that before.

Fantastic experience.

[dramatic music]

NARRATOR: It's now 6:23 PM.

The Doppler on Wheels trucks deployed by meteorologist Josh

Wurman scan the storm with their radar dishes.

The colorful displays paint a complex picture

of the twister's internal structure.

So you want to get to its northeast

and then try to deploy.

It's giving a northeast path.

[dramatic music]

NARRATOR: One of the Doppler's readouts

is the reflectivity display, radar beams

bounced off the storm to show its shape.

The other readout is the velocity display,

showing the speed of the winds, absolutely vital

in understanding tornadoes.

The areas of green and blue represent

winds that are coming towards the radar, which is sitting

right up here.

The areas of brown and red indicate winds going away

from the radar.

In the case of a tornado, which is a circular motion going

counterclockwise, we see very strong, intense--

these blue velocities-- going towards the radar

on the right side.

And, on the left side, we see very strong, very intense winds

going away from the radar on the left side.

NARRATOR: During the storm, Wurman's Doppler display

shows a tiny spot of color in the center,

revealing an astonishing fact.

The area of brown represents winds that are well over

200-miles an hour.

And a jet going into the tornado,

right on this area here, we see an area of red, a contiguous

area of five separate radar measurements

with winds approaching and exceeding 300-miles an hour.

So this area here represents the strongest winds

that we measured-- in fact, that anyone's ever measured.

NARRATOR: The preliminary data shows a wind speed

of 318 miles per hour, at the very top of the F5 range.

No greater wind speed has ever been recorded by anyone.

[wind roaring]

MAN: Damn, that's a monster.

NARRATOR: Some observers believe the tornado is up to a mile

wide.

But appearances can be deceiving.

This simulation from West Virginia University shows why.

The center of the tornado's column of wind

is outlined by a funnel of condensed water inside it.

But when it churns up debris, it looks much larger

to an observer on the ground.

To those watching a tornado like the one in Oklahoma City,

it makes a bad situation seem that much worse.

[wind roaring, explosions]

MAN: Whoa, whoa!

Oh, big time black, Gary.

GARY ENGLAND: Oh, wow.

Is it going--

MAN: I see debris flying-- a big piece of debris flying

through the air.

NARRATOR: The tornado collides with electric lines,

creating bright power flashes.

GARY ENGLAND: Wind speeds, we don't know.

NARRATOR: At Oklahoma City's Channel 9,

the drama is played out live, as weathercaster Gary England

and his storm spotters track the big tornado.

GARY ENGLAND: It was surreal for me.

It was like it was a movie, yet we were a part of the movie.

Because we were looking at live video of this tornado.

I'm talking to our meteorologists in the field.

I'm looking at radar.

Holy cow, you're looking at this thing,

and it's getting ready to move through your city, your town,

and affect your people.

You folks in the path of this storm

have time to get below ground.

You need to be below ground with this storm.

This is a deadly tornado.

NARRATOR: There are some who refused to go below ground

and instead chase after storms, sometimes risking

their own lives for a glimpse of Mother Nature's fury.

[dramatic music]

It's a town in the American heartland, literally wiped

off the map.

NARRATOR: Today, there are only a few signs that Manchester,

South Dakota ever existed--

a small farming community with less than a dozen people

in its last days, a town with a long history, but no future.

NARRATOR: A half-dozen buildings wiped out in minutes--

NARRATOR: --by a monster tornado that stuns

even the most seasoned experts.

I see a roof get lifted off.

[wind roaring]

I hear an explosion.

And then all the walls come up.

And all this debris just starts flying everywhere.

NARRATOR: It is a rampaging force of nature

unlike any ever seen on these windswept plains.

MAN: Go, go, go, go!

NARRATOR: One of the most powerful twisters ever seen

in these parts takes dead aim at the little town of Manchester,

South Dakota.

[wind roaring]

NARRATOR: This is a category F4 tornado, packing winds up

to 250-miles an hour.

It's moving slowly, about 15-miles an hour.

But storm chasers like Jim Bishop and his crew

know to stay out of the way.

The Manchester Tornado, to me, was

so different from all other tornadoes

because it was so big.

And I got so close to it--

--and it was so destructive.

NARRATOR: Later, they are stunned as an entire house is

ripped to pieces right in front of them.

It was like watching the most amazing thing you've ever seen.

And then immediately being, like, just so worried, filled

with sadness, and these deep emotions

of just who's in that house?

NARRATOR: Chaser Tim Samaras is here

to get in the face of this horrific tornado,

placing wind and pressure gauging probes in its path.

And today, he's taking his biggest risk ever.

NARRATOR: It may be slow, but this twister has no mercy--

NARRATOR: --as another house and barn are smashed to bits,

and caught on a storm chaser's tape.

The tornado was approximately a mile

wide as it went through Manchester.

And, at that time, the wind speeds

were close to 250-miles an hour.

Local meteorologist Jay Trobek has seen a lot of tornadoes,

but none like this.

What was interesting is this tornado ramped up and ramped

down.

But it was at its most violent right over Manchester.

NARRATOR: It's a week that has seen more than 50

smaller twisters in the area.

But this massive funnel is the result of three major storm

cells combining to give birth to a monster--

an F4 tornado, growing ever larger as it

heads into Manchester.

The final moments of the two houses on tape

are only a small indication of the devastation inflicted

on the town.

In a matter of minutes, Manchester is a wasteland--

trees, telephone poles, and houses, even the solid brick

town hall ripped straight out of the ground.

Within minutes, we were getting our pictures in here.

And we can see that it was a large tornado.

There was no doubt that this was--

that's the reason why Manchester didn't exist anymore.

NARRATOR: And what of the human casualties?

Storm chaser Tim Samaras was last

seen placing a wind and pressure probe

in the path of the twister about 300-feet away.

NARRATOR: Fortunately for him and his team,

he got out without a second to spare.

It sounded like a waterfall powered by a jet engine.

It was loud.

And you could see debris flying in the air.

And I got out, dropped the probe.

Later on, when we looked at the data,

the tornado crossed the path, right where we were standing,

in 82 seconds.

NARRATOR: And somehow that steel-encased probe

survived as well.

NARRATOR: The probe is six inches high,

weighing about 40 pounds.

Its conical shape helps it to stay snug on the ground,

even in the worst winds, as embedded sensors gather data

on the storm.

TIM SAMARAS: The tip here actually creates

a turbulent wake as the wind field flows over the top.

And it actually causes the pressure to be pushed down

into the ground.

So the higher the wind speed, the more

pressure that the probe gets.

NARRATOR: And the winds of the Manchester Tornado

add up to the most powerful twister ever recorded.

We downloaded the data.

And what we saw was an incredible pressure drop

on the inside of the tornado of 100 millibars, which is a world

record pressure measurement inside of a tornado.

NARRATOR: Millibars are a measurement

of barometric pressure.

The more powerful the tornado, the lower

the pressure at the bottom of the funnel, as the vortex sucks

air upwards like a massive vacuum cleaner.

Normal pressure is about 1,040 millibars.

And when it goes down to 100, there is very little

that can stand against it.

In this tornado, it's like stepping into an elevator

and shooting up a thousand feet in 10 seconds.

We were still in the distance.

But we could tell that it was a very powerful tornado.

NARRATOR: Responding rescue worker Scott Myers

got to see the results of that data

up close in what used to be Manchester.

Buildings were gone.

There was power lines down.

It was a major disaster for that town.

NARRATOR: Amazingly, there was not a single human fatality

as a result of the tornado.

The houses seen destroyed on tape had been safely evacuated.

Most residents fled ahead of the storm.

NARRATOR: Several deadly tornadoes

touched down in central Oklahoma on May 3, 1999.

The strongest, with an F5 rating,

tracked over an hour and a half along a 38-mile path

through Chickasha, just south of Oklahoma City and surrounding

suburbs.

[horns honking]

WOMAN: Oh, my god!

Oh, my god!

Oh, my god.

NARRATOR: Meteorologist Gary England warned the public

to seek shelter.

GARY ENGLAND: You folks in the path of this storm

have time to get below ground.

You need to be below ground with this storm.

This is a deadly tornado.

NARRATOR: Rick and Teresa Isbell are among those hearing

England's warning.

The tornado is headed toward their home.

I grew up in the panhandle of Texas and here in Oklahoma.

And I've seen a lot of tornadoes.

I've been known to set in my lawn chair

in the front yard with my glass of tea and watch them go by.

They never concerned me that much.

But this one here was so getting so big

and it was not bouncing around.

It really got my attention.

MAN: Getting ready to cross the river, crossing the South

Canadian River, near Southwest 149th Street--

NARRATOR: The TV broadcast shows the twister is just four miles

away from the Isbells' home.

I knew where it was headed.

And that's when I decided to bail out of here and take off.

NARRATOR: Their only hope is to reach

the home of Rick's aunt, who has a storm

shelter in her backyard.

He was driving like a maniac.

And I told him, I said, "If you don't slow down,

you're going to kill us before the tornado does."

NARRATOR: Nearby other residents,

also ready to seek shelter, have their video cameras rolling

as the tornado approaches.

MAN: Yeah, it's headed right at me.

I got it in my camera view.

It's headed right in front of me.

And I'm fixing to go for cover.

NARRATOR: With only a few minutes to spare,

the Isbells make it to Rick's aunt's house and their waiting

storm cellar, just as the tornado passes nearby.

What we didn't know it was our area had been hit.

[dramatic music]

NARRATOR: The twister slashes first

through the Isbells' neighborhood

in southwest Oklahoma City, and then through neighboring Moore,

where some of the worst damage occurs.

MAN: It's coming through the city of Moore right now.

NARRATOR: Hundreds of homes are flattened.

West Moore High School takes a major hit.

And a two-story metal church building

is completely destroyed.

The largest projectile is a steel tank,

tossed nine 900-feet.

And a bathtub, with a woman hiding inside,

is thrown 300-feet.

Incredibly, she rides the distance and survives.

In another 15 minutes, the tornado

roars north through Tinker Air Force Base, where it starts

to lose steam.

MAN: It might have died.

MAN: Yeah, I don't see it.

I think it might be gone.

NARRATOR: The horror ends at 7:48 PM,

as the tornado dissipates in Del City, just five miles

from downtown Oklahoma City.

An average tornado's two-minute lifetime leaves a damage path

two miles long, 50 yards wide.

But this one had remained on the ground for 85 minutes,

scoring the earth with an ugly scar 38-miles long, and up

to a mile wide.

It was actually stripping the grass down

to the bare red Oklahoma dirt.

And the scour mark that it left looked

like there were 10,000 herd of buffalo marching on through.

It literally scoured the landscape.

NARRATOR: When the counting is done, 43 people are dead,

795 are injured--

remarkably low numbers, given the magnitude of the tornado

outbreak.

And the reason that tornado didn't

kill a large number of people, I believe, is good warnings.

NARRATOR: But while people can take shelter, a city cannot.

May 3, 1999 leaves Oklahoma City with 2,314 homes destroyed;

7,478 damaged.

And the cost?

$1.2 billion.

It was just kind of a shock.

It was just pure devastation, like somebody just dropped

a bomb on our neighborhood.

Just leveled the whole neighborhood.

NARRATOR: The 318-mile per hour winds

are a world record, the most intense tornado ever measured.

It mauls the earth for nearly 40 miles.

The devastation is unbelievable.

I didn't recognize my house when I was brought

into the neighborhood.

There were no points of reference.

It was just one big mass of debris.

[dramatic music]

NARRATOR: The terrible storm leaves 43 people dead.

And it becomes known as history's

first billion-dollar tornado.

CHUCK DOSWELL: The fact that this

was such a devastating tornado is the result

of it being a violent tornado going

through a metropolitan area.

But Oklahoma City is not a major metropolitan area.

It's a good-sized city.

But there are many other cities across the US

that are much larger.

And to have a violent tornado go through one of them

in the future offers the potential

for even greater devastation.

NARRATOR: May of 1999 wasn't the only time a killer tornado hit

Oklahoma City.

After two days of severe thunderstorms,

on the evening of May 20, 2013, a powerful tornado

tore through Oklahoma City and its surrounding cities

and towns.

It was given a maximum rating of EF5.

It claimed 24 lives, injured hundreds of people,

and caused $2 billion in damage.

This event was the most deadly and devastating tornado

in the United States that year.

Tornado Alley is home to a number of large cities--

from St. Louis to Omaha, to Kansas City,

Dallas, Oklahoma City, and Chicago.

The next tornado could strike any of them.

MAN: Brace yourself.

We're parked on the wrong side of the freakin' road.

MAN: Use your wiper blades.

WOMAN: Uh uh.

GARY ENGLAND: This is a major tornado,

significant proportions, wind speeds we don't know.

But it's going to level most houses.

[wind roaring]

Conventional housing is built to a building code.

And that building code states that you

have to build to a 90-mile per hour, three second gust.

NARRATOR: But what building code can protect us from a killer

wind three times more powerful, such as the 318-mile per hour

vortex that struck Oklahoma City?

If you're talking about a big F5 tornado that's a mile wide,

that can cover the entire metroplex,

we're going to be seeing a major, major disaster here.

NARRATOR: That's why Scott Ray and a team of computer analysts

in Dallas are trying to second-guess ruthless nature.

Ray has led a detailed computer study of the damage the 1999

Oklahoma City tornado would do if it were to strike

a major city like Dallas.

This giant metroplex is packed with targets

of destructive opportunity--

six million people, one million homes,

60,000 commercial buildings.

This computer modeling begins with the data collected

by scientists, like Tim Marshall and Chuck Doswell.

After the Oklahoma City Tornado, each took part in surveys,

carefully photographing the tornado's damage

and cataloging each building within the F0 to F5

range of the Fujita Scale.

The F numbers from the Oklahoma City damage survey

are used to create maps.

A US Air Force photo of the damage track is the template.

The F Scale damage is posted for each house surveyed.

And then it's just a matter of connecting the dots

to create a detailed map of the tornado's path of destruction.

The color coding is a cold, clinical illustration

of the massive total devastation radiating out from the center,

fading at the edges.

[wind roaring]

There is a myth that you cannot build a home to resist

a tornado.

It is not possible to build a home economically to resist

F4 and F5-intensity winds.

But only a small fraction of the path

ever experiences those winds.

NARRATOR: Most houses are hit by F3 winds or below.

Here, some houses stand up better than others.

Those left standing are the ones built using stronger joints

than their weaker neighbors.

A worker demonstrates how the sill plate

is nailed to a typical house foundation using

common narrow cut nails.

Let me show you how deep this cut nail actually

goes into the slab foundation.

If you look down here, as this head gets driven down in here,

you only get about a half an inch of penetration

into the slab.

NARRATOR: A tornado could rip out this sill

in the blink of an eye.

Look what happened here when the cut nail was actually

pulled out of the foundation.

It broke off a piece like this, just lying like that,

with a huge area here out of the slab.

Now this is what we see time and time again after tornadoes that

hit houses.

NARRATOR: The conclusion is clear--

strengthen the joints that hold houses together.

Cost effective solutions include bolts to attach the sill

to the foundation.

The roof, another weak point in many houses,

is made more wind resistant by nailing it to the frame

with hurricane clips.

These pieces of hardware could keep the roof from flying off

in tornadoes, as well as the hurricanes for which they are

named.

But even the best construction isn't enough to save a building

when a tornado strikes.

[dramatic music]

Theodore, Alabama, a small town nestled

along the Gulf of Mexico.

It's far from the Midwest's infamous Tornado Alley,

but it's still no stranger to twisters.

It's part of what would be called "Dixie Alley."

And they have an enormous amount of tornadoes

there during the year as well.

Alabama has two different tornado seasons--

one in the spring, and one in the fall.

And it's all determined where the polar jet stream is.

During the springtime, the polar jet stream

starts dipping way down to the south, toward the Gulf

of Mexico, where Alabama, Mississippi, Georgia is.

And then that happens again in the fall.

MAN: We've got a funnel cloud just over Dog River.

Hasn't reached the ground yet.

NARRATOR: Trouble is brewing in the skies over Alexander

Hardware, a mom and pop store, run by Margaret Alexander

and her husband, Tony.

A wall of menacing thunderstorms has staked a claim on the area.

This system was very big.

It stretched all the way from Louisiana

up till about Tennessee.

And one of the reasons that was, was because there

was a lot of Gulf moisture at that time

and clashing right with cold polar air.

And these two air masses start rotating.

They don't like one another.

That's when you can get some powerful tornadoes.

NARRATOR: Inside the store, the Alexanders

are oblivious to the disaster bearing down on them.

They help a customer, while in back an employee

repairs a lawnmower.

Security cameras show that no one spots the danger until it's

literally on the doorstep.

But, by then, it's too late.

[wind roaring]

One of the world's deadliest forces

invades the Alexander's store, tearing the couple's business

to shreds.

[wind roaring]

Every square inch of the place is ripped apart,

including the back room, where the tornado instantly

turns tools and merchandise into lethal weapons.

[wind roaring]

This tornado is an EF1 to EF2.

The winds are strong enough to break out the doors and windows

and send all of the contents of the store flying.

That's the biggest hazard for people in this store.

EF2 winds, they range between 111 and 136-miles an hour.

These are building-damaging winds.

We're seeing roof failure there.

We're seeing doors blow open.

We're seeing the wind attacking.

These are things that can destroy enough buildings,

throw enough debris around to cause millions of dollars

worth of damage, and kill a few unlucky people.

NARRATOR: The violent vortex sends

shards of metal and debris spiraling through the store.

[wind roaring]

Part of that tornado, it looks like to me, actually

went inside of that area.

Because look at all of the rotation of the paper,

of the tools.

It's possible that a tiny portion of that tornado

ended up inside.

NARRATOR: Though the sight of a tornado

should strike terror in anybody's heart,

not everyone takes cover.

Both Margaret and the customer linger near the door,

even as the intruder zeros in on them.

We have studied tornado behavior.

When people hear about tornado warnings,

they still want to go outside and see it for themselves.

They always need extra proof.

And, generally, that proof is visual proof.

They want to see the tornado.

They hear the warnings.

But where's the tornado?

Seeing is believing.

[wind roaring]

NARRATOR: Margaret's husband warns his wife

to back off, a move that saves her life.

The counter had an area underneath there

that we took cover under.

If my husband hadn't have been there,

I would have probably been swept down that aisle.

NARRATOR: But their customer isn't so lucky.

He was at the door himself.

And so when Tony and I went for cover, he didn't have cover.

And so he got swept down the aisle with the debris.

[wind roaring]

NARRATOR: Amazingly, the man survives the onslaught

with only minor cuts and bruises.

You're inside a store, loaded with all kinds of metal,

and wood, heavy objects.

The thing you want to do is get into the center

of that building and get underneath a very, very heavy

table to try to protect yourself,

to not get plucked out by the wind, or thrown around.

Don't be looking around.

Don't be standing up, making yourself

a big target for flying debris.

Seek shelter.

[wind roaring]

NARRATOR: After wreaking incredible havoc,

the assailant moves on.

It was all over in about 45 seconds.

Then it was just like complete silence.

These things strike fast and hard, and they're gone.

[dramatic music]

NARRATOR: Though this twister was relatively small,

Alexander Hardware has been all but obliterated.

MARGARET ALEXANDER: The roof had come in pieces.

The wall, over on the other side, it completely caved in.

The Parts Room was in shambles.

But our lives were there.

And that was the main thing.

We were all safe.

It's miraculous that no deaths were reported and very

few injuries.

An EF2 can do a considerable amount of damage.

NARRATOR: The Alexanders soon rebuild.

And Margaret hopes a visitor this destructive never

darkens her doorstep again.

MARGARET ALEXANDER: There's a possibility of tornadoes,

and I take heed of it.

We had no idea it was going to be a tornado at our front door.

[wind roaring]

NARRATOR: A tornado is invisible unless it is filled

with either condensed water vapor, which makes it white,

or with debris, which turns it dark.

It's bad enough when forceful winds do their damage

to property.

But debris makes things worse.

A poorly-built house will throw off

debris that can damage a sturdier house downstream.

Water tanks, bathtubs, bricks, pipes, and lumber

are wind-driven battering rams, blowing away houses

that might otherwise survive.

Because wind-borne debris is such a major factor in damage

analysis, researchers at Texas Tech University

have developed a special instrument called the "Debris

Impact Cannon" to study it.

Clear.

Three, two, one.

[dramatic music]

I earned my degrees from Texas Tech.

And, of course, one of the things that we do

is we have this cannon, and we shoot boards through walls.

And it demonstrates quite clearly

that you need to have some pretty good protection

on your walls.

[clatter]

NARRATOR: A 15-pound two by four,

traveling 100-miles per hour, is the most common kind

of tornado debris.

And that's what the cannon is built to fire.

Well, the two by four, everybody

is pretty familiar with.

And we've seen a number of examples where two by fours

go through things.

They go through the roof deck.

They go through brick walls.

I've even seen them go through refrigerators.

So the two by four is a fairly common building material.

And we do see it flying around a lot.

NARRATOR: The Debris Impact Cannon is also used

to test building materials--

[clatter]

--especially those used in safe rooms

designed to protect people inside their houses

during tornadoes.

[clatter]

Safe rooms are generally made of reinforced masonry,

jacketed with a thick steel frame, so solid and so strong

that they are impervious to debris driven by 200

and 300-mile an hour winds.

But what if you have no safe room?

Then you need to be told where to go by weather forecasters.

20-miles per hour.

Temperatures--

NARRATOR: Using a combination of radar, satellites,

instant communications, and supercomputers,

modern forecasters continue to increase warning times.

--steady winds.

10-miles per hour--

The average lead time, over the last several years,

has now increased to 13 to 15 minutes for a tornado warning.

NARRATOR: That's just enough time to get to a safe place,

even if it's only the innermost room of your home.

As these wrecked neighborhoods show, time and again,

the inner rooms usually survive.

Tornadoes have occurred in the United States

for hundreds of years, with the first recorded sighting made

by Massachusetts Bay Colony Governor John Winthrop in 1643.

But they aren't just an American phenomenon.

Tornadoes occur in many parts of the world.

The Bangladesh Tornado of April 26, 1989

is one of the deadliest on record.

Yet the United States continues to be the country that

gets hit the hardest.

[wind roaring]

The tornado experience to me made

me realize how precious life is, how quickly your life can

change.

[wind roaring]

Don't be looking around.

Don't be standing up, making yourself

a big target for flying debris.

Seek shelter.

These things strike fast and hard, and they're gone.

[wind roaring]

You know, you never really think about tornadoes.

But it's very devastating.

And if you take them lightly, you'll regret it.