Original subtitles

Viewers like you make this program possible.

Support your local PBS station.

A freakish kind of weather event...

We should not be here.

I know. I'm shaking right now.

...is now striking again and again.

People were panicking,

running, taking cover.

Intense...

Batten down the hatches

for the potential for straight-line wind gusts

in excess of 75 miles an hour.

Highly localized.

That thing just collapsed right on those mountains

and all that air is just exploding.

And devastating.

MAN Get away from the glass!

It sucked windows out.

There was glass everywhere.

They fall from the sky without warning.

Explosions of wind and water so violent,

they can flatten homes in seconds.

They're known as rain bombs.

And they're getting stronger.

The damage each year just continues

to pile up and up and up.

Now researchers are attempting to understand

these destructive weather events.

In some cases, it can look like a bomb went off.

Trying to predict where they'll drop and when.

It's not safe to be outside-- you've got about 20 minutes

until this severe storm passes through.

"Rain Bombs."

Right now, on "NOVA."

August 2011.

The Pukkelpop Music Festival, Belgium.

Out of nowhere, the skies darken...

...as powerful winds gust at over 80 miles per hour.

MAN Please exit the tent!

Stages collapse.

Very quickly, within a couple of minutes,

it became probably the heaviest rain I'd ever seen.

Lauren Beehan was 19 when she and her friends

traveled from Ireland to Belgium for the festival.

You couldn't see anything, really.

There was wind blowing debris.

It was very much a case of feeling like we were trapped.

For it to turn from such a sunny, cloudless day

to something apocalyptic in the space of 20 minutes

is frightening.

It's like something from a disaster movie.

140 people are injured

and five festivalgoers lose their lives.

August 2024.

A super-yacht called the Bayesian

sinks off the coast of Sicily.

CCTV from the shore that night

catches the vessel's mast, lights barely visible,

in the 100-mile-per-hour wind gusts and rain.

It drags anchor, then capsizes.

Divers recover seven bodies from the wreckage.

July 2018.

In heavy rain at Durango International Airport,

Aeroméxico Connect Flight 2431 is cleared for takeoff.

Jesus !

No sabemos si fue un rayo

o un problema mecánico.

The aircraft crashes back down to Earth

before it even clears the runway.

Miraculously, there are no fatalities.

Each of these events was caused

by a mysterious weather phenomenon,

recognized only in the last 50 years.

Each began with a thunderstorm,

but what followed was much more violent and unexpected.

Highly localized, sudden, and extreme rainfall

and low-altitude, high-speed winds.

They're nicknamed rain bombs,

but scientists call them downbursts.

So, what are they?

And what causes them?

Mike Olbinski

is one of the world's foremost thunderstorm photographers.

After 15 years of chasing storms,

he's mastered the art of being

in exactly the right spot at the right time

to photograph an elusive weather phenomenon.

Rain bombs exploding from the sky.

His images can help scientists understand

how these weather systems form

and how they detonate.

We have an updraft going up right to our west,

and then this big storm is forming right behind it,

and I can see it on the horizon,

so I think we need to get a little bit more west.

Growing up in Phoenix,

we used to watch lightning storms, you know,

outside at night.

I loved them, and I've always loved them,

and I traced it back

to seeing a lightning bolt strike behind my house.

I still have this insane, vivid memory of it happening.

Mike is on the hunt for rain bombs.

These intense weather events are striking

with greater strength than ever.

To track one down, he first needs to find

a developing thunderstorm.

But what is the difference

between a rain bomb and a run-of-the-mill thunderstorm?

In a normal thunderstorm,

you get heavy rainfall, lightning, and sometimes hail.

And this can happen over hours.

A thunderstorm can drop rain at about two inches per hour.

A rain bomb can triple that rate.

And in a rain bomb,

the rain and hail aren't just falling to the ground.

They're being thrown down by hurricane-force vertical winds.

What does a rain bomb look like?

It looks a massive volume

of rain and cold air

coming from cloud base to the surface.

Across the planet,

there are 2,000 electrical storms

generating thunder and lightning

at any given moment.

Each one of them releases more energy over its lifetime

than the 15-kiloton atomic bomb dropped on Hiroshima.

Every rain bomb forms from a developing thunderstorm,

but to understand how,

we must first understand how clouds form.

When sunlight hits the Earth, the surface heats up,

and water from oceans, lakes, soils, and plants

starts to evaporate, turning into water vapor.

That water vapor and the warm air around it start to rise.

As it starts to rise,

it takes all of the water vapor near the surface of the Earth

up into the atmosphere.

As it lifts that up in the air, that parcel of air cools.

The colder the parcel,

the less able it is

to carry around that water vapor,

and so it forces it out into the formation of cloud droplets.

Clouds form where the water vapor condenses

into tiny water droplets, so small and light

that they stay aloft, instead of falling as rain.

The altitude where this happens is called the cloud base.

You see lots of little clouds developing,

and they all have the same cloud base.

So the cloud bases are actually occurring

at the same temperature, and hence the same height.

In Arizona, the summer monsoon season has arrived.

It carries moist, warm air from the Gulf of California,

the perfect fuel for thunderstorms and rain bombs.

We can feel it in the air,

that it's really humid out, there's moisture,

it's warm, so we've got the environment

for, for storms to form.

We're seeing these strong

cauliflower kind of shape to the top.

When you're seeing that,

you've got to imagine how intense that is

to go from nothing to this sharply defined cloud.

And then a couple of them get a little bigger,

and then you get something like this, where, boom, it erupts.

If the conditions are right,

these simple clouds can turn into thunderstorms.

When you have

these puffy, fluffy clouds that you see in the sky,

there are some interesting things going on inside.

Condensation is happening,

and heat is actually being released

as water vapor is changing to water.

As the water vapor cools,

it condenses into droplets

that form a cloud, warming the surrounding air.

The now-warmer air rises, creating more updraft,

lifting more air higher into the cooler atmosphere,

where even more water can condense,

which further warms the air.

If the conditions are right,

with enough moisture rising into cold air above,

this fuels a positive feedback loop

that intensifies the cloud's growth.

I see, like, a whole line of updrafts going up,

so I like that.

A lot of these tops today, they just look

really strong.

Sometimes you got the towers going up,

but they don't have the same kind of powerful look.

They're bubbly like a cauliflower,

but they're just a little less intense.

Well, a couple of these, if you look at them,

they just look like there's so many areas

where it's just knuckle-y

and explosive-looking.

Oh! I just saw two big bolts strike

way out there on the horizon-- whew!

But I think something big's going to happen here.

It's a nice, large, dark area.

This is probably going to turn into a really strong storm.

I would expect, I would hope.

I'm trying to catch some lightning right now.

I'm doing two timelapses.

Lightning is an indicator

that the updraft is tall enough to have ice and hail.

Ice and hail are key ingredients

that drive the most powerful rain bombs.

But how does something as solid as ice or hail form

and stay aloft in the atmosphere?

When water vapor condenses in clouds,

it releases an extraordinary amount of energy.

That makes our clouds very turbulent

and that lifts the air higher up in the cloud.

At some point in time,

that air will cross over what we call the freezing level

to form things like snowflakes and hailstones,

and that change in phase, of course,

releases more energy.

This energy, in the form of heat,

drives the further growth of the cloud, expanding upward

to the very top of the troposphere,

up to 12 miles above ground level.

Above the troposphere sits a warmer band of air

called the stratosphere.

This warm air acts as a lid preventing the cloud

from climbing any higher, so it spreads out flat,

forming a distinctive anvil shape.

So we've gone from the development

of a tiny little fluffy cloud

to these very tall, extensive storms

that are now carrying around

large amounts of hailstones and snowflakes.

This storm is now seriously ready to do business.

Lightning bolts are a telltale sign

that a cloud has developed into a thunderstorm.

Raindrops get so big,

they're too heavy to be held by the cloud's updraft,

and so it begins to rain.

Or, if conditions are right, it can go on to develop

into a violent rain bomb.

To understand why some thunderstorms

collapse into rain bombs,

it helps to know what's going on inside that rain cloud.

One way to uncover that

is to analyze the stuff that falls out.

Particularly hailstones, icy chunks of frozen cloud.

Over the summer of 2025,

storm researchers teamed up on a project called ICECHIP

to collect hailstones

from thunderstorms striking the Great Plains.

BECKY ADAMS-SELIN: The ground teams,

the teams looking at what kind of hail fell at the surface,

is really what made this campaign unique,

because other campaigns, you know,

would go and, and look at, at storms with mobile radars,

and that's a lot of great information,

but only ours also tried to really fully characterize

what kind of hail was down at the surface.

The ICECHIP team brings the hailstones

to a cold lab in Boulder, Colorado.

Here, at below-freezing temperatures,

atmospheric scientists Anthony Bernal Ayala

and Becky Adams-Selin

process and analyze each of the thousands of samples.

Large hailstones are extremely valuable

in understanding more about the thunderstorm they came from.

Once you get the hailstone, you can actually just go ahead

and cut a thin slice out of it.

And you polish it up so it's an even thickness.

You can get a lot of information just by looking at the slice.

You can see different rings in the hail,

and much like tree rings,

those represent different conditions

under which the hail was growing in the storm.

When we look at hailstones

and we look at the cross-section,

one of the things that we look at

is whether the layer is opaque

or whether layer is clear.

When you look at that clear layer,

you're looking at where there is warmer sub-zero temperatures,

so it's a little bit warmer in the cloud,

where liquid water freezes slowly,

and because this freezes slowly,

that allowed the air bubbles to escape.

So it's gonna be clear-- there's not gonna be a lot

of air bubbles trapped in this layer.

When you look at the opaque layer,

because it's in temperatures in the cloud that are very cold,

it's gonna freeze very rapidly.

So, because it freezes very rapidly,

it actually traps a lot of air bubbles in that layer,

so that it actually looks opaque.

But why would a single hailstone

have both clear and opaque layers?

And what does that reveal about how the hailstone formed?

The hailstone had to have been moving around in the storm

to experience these different conditions

and to create the different layers.

We think that it's actually rotating somehow

around the updraft

to accumulate all those layers

that we see in the cross-section.

These layers are evidence

that the hailstones are continually rising and falling

inside a developing thundercloud.

This hailstone spent most of its time

in very cold temperatures in the cloud,

but for a very short period,

it actually went through a warmer side of the cloud.

Then it went back, a very cold temperature,

then it went back, a warmer section of the cloud,

where it probably fell and then it was collected at the surface.

To grow to two inches wide,

this hailstone most likely spent over half an hour

being lifted and dropped inside the storm.

There's updrafts, there's downdrafts.

There could be hail.

There could be circulations or rotations

inside that cloud.

These intense storms are very turbulent.

They have regions where air is rising very rapidly,

sometimes at speeds of 150 miles per hour.

This mixing of hail and ice provides the energy necessary

for the storm to produce thunder and lightning.

In mature thunderstorms,

like the one that made Anthony's hailstone,

immensely powerful updrafts

can suspend over a million tons of hail

miles above the ground.

It's actually quite incredible

that storms are able to suspend

this large mass of liquid raindrops

and other ice, like hail and snowflakes,

so high up in the atmosphere.

What happens to this core of rain, hail, and ice

determines whether the storm remains

a regular thunderstorm

or unleashes a rain bomb.

Dude, that looks freaking awesome.

That's just plummeting-- that's, like, a downburst happening.

When you see that middle rain shaft area,

where it looks like a blob,

that's usually a good telltale sign

of a downburst happening.

Oh, man.

This is stunning.

In a fully developed thunderstorm cloud,

what goes up must eventually come down.

The cloud's updraft begins to peter out

as rising air cools and sinks back toward the ground

as a downdraft.

This is what happens in a standard thunderstorm.

But in a rain bomb, things are different.

Because in a rain bomb,

a sudden, extremely strong downdraft

overwhelms the updraft,

causing the cloud's core of ice and hail to collapse

all at once.

Two processes drive this sudden downdraft intensification.

The first is that, as the rain and hail start to fall downward,

they drag on the air.

So they pull the air down toward the Earth.

When massive amounts of rain and hail begin to fall,

they help generate a downward rush of air,

which can act as the rain bomb's trigger.

But that's not all that's required

to get a rain bomb started.

The second, more important process

that accelerates this developing downburst toward the ground

is evaporation.

Evaporation is a cooling process.

You experience it when you step out

of a swimming pool or your shower.

When you've got drops of water on your skin,

as these drops evaporate, your skin feels very cold.

If winds blowing into the cloud are dry,

they can rapidly evaporate raindrops,

as well as melt ice and hail.

This cools the surrounding air, making it denser and heavier.

This very cold air, very dense air, has to sink.

So it's going to rush toward the surface,

taking all of that large mass of rain and hail.

As rain and hail descend from the cloud,

if they hit more dry air,

the evaporation can accelerate further.

As the raindrops fall below cloud base

into this drier air,

they will evaporate in that location, too.

This, of course, is going to really intensifies

that cooling process.

This very cold, dense air then rushes toward the surface,

creating these phenomenal scenarios

called downbursts or rain bombs.

The downdrafts can intensify

into hurricane-force vertical winds,

driving the cloud's core of hail, rain, and cold air

downward, slamming it into the ground.

Sometimes, the downburst's rain

can completely evaporate before reaching the ground,

creating what scientists call a dry downburst.

And all of these downbursts, both wet and dry,

can strike in just a few minutes,

in a remarkably narrow column,

as small as just a couple of hundred yards across.

And as our atmosphere warms,

they're becoming more and more powerful.

It actually can be quite a frightening moment.

There's a lot going on.

There's lightning, there's hail, there's very heavy rain,

and then, of course, the strong wind.

Storm chaser Hank Schyma has been caught

under a powerful rain bomb.

There was a day

where I get slammed by a downburst.

The rain really picks up and gets really strong,

everything turns white, and then, all of a sudden,

I can see that I'm about to drive off the road.

You can feel the winds rocking your car,

and, and the winds are picking up

sand and things in the road,

and they're slamming them into your car.

It's really terrifying and scary.

Strong winds are a key element of downbursts.

They slam cold air into the ground at high speed.

And this air has to go somewhere.

They can't go into the ground, so they spread out

horizontally in all directions.

So, you see extreme surface winds.

Cold air hits the ground

and pushes out radially from the heart of the downburst.

This outflowing air--

remember, it's very cold, dense air--

we refer to as a cold pool,

because it is a cold pool of dense air.

These advancing banks of cold air can kick up dust,

creating the distinctive dust storms

often seen in the American Southwest.

Dusty cold pools are called haboobs.

And they create all sorts of severe weather,

including visibility issues,

road accidents, and breathing issues.

The dust makes the turbulent gust front

of an advancing cold pool

easy to see.

But even when no dust is present,

this billowing front of cold air is still there.

And it's these fierce straight-line winds

that inflict the most damage.

These winds are

strongest near the surface.

If you compare that to something like a hurricane,

a lot of the strength in a hurricane

exists higher up in the atmosphere.

But for downbursts, they occur very close to the surface.

Trees will just flap down to the ground,

and these wind gusts are so strong

that you cannot stand on your own feet anymore.

In some cases, it can look

like a bomb went off.

Literally, that air hits the ground at low levels

and spreads out in all directions.

Those winds are what we call straight-line winds.

They are not turning like a tornado turns.

They are following straight lines

away from where the downburst hits.

This might explain what happened

to Aeroméxico Connect Flight 2431

when it took off from Durango International Airport,

en route to Mexico City.

The rain, while heavy, was not extreme.

There were storms in the area,

but the tower had cleared them for takeoff

and had told them that they actually have headwinds,

which would provide them lift for takeoff.

Without realizing it, Flight 2431 flew through a downburst.

In just seconds, the plane experienced

a near 180-degree shift in wind direction.

The plane was about 30 feet off the ground,

a very susceptible time on any takeoff,

and this tailwind, it swung from being an uplift

to a sinking motion.

Without the lift generated by a headwind,

the plane plummeted and crashed into the runway.

Luckily, everyone managed to escape

before the plane was fully engulfed in flames.

This wasn't the first passenger jet

to crash in similar conditions.

June 1975.

Eastern Airlines Flight 66 crashed on approach to JFK.

August 1985.

Delta Flight 191 crashed on approach to Dallas Fort Worth.

July 1994.

U.S. Air Flight 1016 crashed on approach

to Charlotte Douglas International Airport.

Those tragic accidents in the '70s and '80s

led to a lot of very significant research in downbursts,

how they operate, and then subsequently,

the technology that we need to warn pilots.

A lot of the airports in the U.S.

are fitted with these weather radars,

but there are many of the airports around the world

do not have this technology.

Aeroméxico flight would not have taken off

had they been aware of the fact

that they were just about to hit a downburst.

When investigators study the loss

of the supposedly unsinkable Bayesian yacht,

which went down on August 19, 2024,

they discover that before it capsized and sank,

it had dragged its anchor around 400 yards

in a dead straight line.

The Bayesian was anchored

off the north coast of Sicily.

It was in a bay, it was next to another yacht.

This CCTV footage from a camera onshore

about 600 feet away

reveals the boat in the distance.

What ended up happening was,

as these really strong straight-lined winds

hit these yachts,

they dragged anchor in straight lines.

That indicates it was a straight-lined wind,

as opposed to the kind of rotational wind

you would get from a tornado.

And it was a very large yacht with a very tall mast

and it would appear

that the downburst and associated cold pool

was actually able to roll it over

beyond its point of stability.

The yacht succumbed to the same type

of extreme low-altitude, straight-line winds

that led to the crash of Flight 2431.

At the Pukkelpop Festival in 2011,

the hail and howling winds struck an area

less than a hundred yards across.

This was a very narrow downburst.

This is what made it so unusual.

You would normally expect such power

from systems that are larger,

where they can transport

more rain and more hail and more wind to the surface

than in a 100-meter-wide downburst.

So, a really remarkable event.

These real-life tragedies reveal

the destructive potential of powerful rain bombs:

intense, highly localized, and short-lived.

But a storm that hits Houston in May 2024

has all the hallmarks of a downburst,

except that it is much bigger.

It travels around a thousand miles

and it lasts much longer than a single downburst--

more than 12 hours.

A line of severe thunderstorms

is racing into our Greater Houston area.

You should batten down the hatches

for the potential for straight-line wind gusts

at about 70, 80, to 90 miles an hour.

National Weather Service forecaster Amaryllis Cotto

is on call at the Houston/Galveston office

27 miles southeast of Downtown Houston

when the storm hits.

The storm developed very fast

in areas of West-Northwest Texas at around 9:00 a.m.,

and so we could see how fast it was moving.

It was already affecting the Houston metro area

by around 5:00 to 6:00 p.m.

It's not safe to be outside.

You've got about 20 minutes to get hunkered down

on the first-floor interior room of your home, away from windows.

That's the safest place to be

until this severe storm passes through.

It was devastating Houston.

We had a lot of tree damage.

We had millions of people without power.

Hank and Natchaya Schyma

are five miles north of downtown when the storm hits.

He starts recording the storm from his car.

Suddenly, it goes from daylight to darkness, and chaos hits.

Here it comes.

Holy (bleep)! Holy (bleep)!

Yup, hang on, I've got it.

Um, we should not be here.

I'm shaking right now!

HANK SCHYMA You can't see a block in front of you

just because of the whitewash of wind and rain,

and trees are swaying,

and downtown Houston is raining glass,

as windows are, are failing all up in the skyscrapers.

MAN Move away from the glass!

The winds associated with this system

were hurricane-force winds in the lower levels.

It sucked windows out-- there was glass everywhere.

And in addition to the sucking motion,

inside the buildings,

the pressure is now higher than outside.

So you get this explosive force

that forces windows and glass out of the buildings.

It's the signature of a rain bomb.

Super-strong ground-level winds shattering

any weak windows along their path.

Telltale signs of straight-line wind damage

are seen all over the city.

They pull down power lines across Houston

and plunge one million people into darkness.

But the Houston storm isn't the size of the storms

that hit Pukkelpop or sank the Bayesian.

It's over 50 miles across

and leaves a path of devastation

across the 10,000-square-mile Houston metro area.

Rain bombs just don't grow this big on their own.

They need to gang together to become this large.

But how?

22 miles northeast of Fort Collins, Colorado.

Atmospheric scientist Sue van den Heever's 20-strong team

is out in the field.

I think the forecasters are keen

to have some surface measurements,

Okay. They are trying to assess the moisture.

Her team deploys drones engineered to withstand

extreme weather.

They measure the outflow winds

when the cold air in a downburst crashes to Earth

and races across the landscape, forming the cold pool.

We've launched what we call the flying curtain.

And we're flying a wall of six drones.

We have a lower level of drones

and an upper level of drones.

We have a lot of instruments

that can measure the temperature,

the moisture of the atmosphere.

We've got anemometers on there that can measure the winds.

And this allows us to make measurements of the variability

of the atmosphere,

and as the cold pool advances on us

and blows through us,

we are able to make

that measurement in time, as well.

So there's a lot

that we are characterizing about these cold pools.

Sue and her team

are tracking a storm a safe distance away,

beyond the horizon.

Radar shows that it has produced a downburst of intense rainfall.

The air that slammed into the ground

is now spreading out across the plains in a cold pool,

coming toward them.

Their radar tracks the dust kicked up

by the advancing bank of fast-moving cold air.

So we're expecting

that cold pool to come through

within the next few minutes,

so we're waiting to try

to collect the data.

The team will release weather balloons up into the cold pool,

to measure temperature, pressure,

humidity, and moisture.

This cooling of the air you can feel,

and the wind you're feeling,

that's this boundary that's actually starting to hit us.

So we're going to release that balloon.

Everybody ready?

Three, two, one.

Oh, and there's some thunder.

Please release.

30 minutes after the rain bomb dropped,

that bank of cold air,

here graphically rendered to be visible,

has covered the 17 miles from the epicenter of the storm

and breaks over the flying curtain of drones.

On the ground, the team analyzes the data.

So right here, we're, we're looking at data

from the balloon that we just launched.

What we're looking at is pressure, moisture,

temperature, and relative humidity.

And this is telling us

the depth of the cold pool

that just came through.

So right now, based on the temperature data,

we're seeing a decrease in temperature

that is going about 500 meters high.

The team has learned the cold pool

reaches 500 meters, or about 1,600 feet high,

but that's not all.

These balloon observations allow the team to measure

what's happening to the air above the advancing cold pool.

What they've found is that the cold pool

acts as a wedge, pushing up an updraft of warm air.

When we have a storm

forming a really strong downburst

and its associated cold pool,

that lifts the surrounding air

up and over the edge of the cold pool

and forms a new updraft.

That updraft can go on to build another really strong storm.

That storm can then, of course, make its own downburst,

its own new cold pool,

which can then form another updraft,

and so we get into this cyclical process of updraft formation.

Background winds can stretch downburst cold pools

from circular outflows into fan-shaped fronts.

If atmospheric conditions are primed

for multiple thunderstorms,

the cold pools can merge into one broad line

of advancing cold air.

The advancing boundary lifts warm air ahead of it.

This rising warm air feeds a new generation of updrafts

and helps build an even larger storm.

It's a self-sustaining cycle

of updrafts, downbursts, and cold pools

that sweeps across the landscape.

Meteorologists call this a derecho.

One thing that distinguishes derechos

from other types of wind systems

is their sheer size and how long they can last.

The longest one on record is some 1,300 miles.

Derechos can stick together

for time periods of six to 12 hours.

So these are extensive, very dangerous wind storms.

The 2024 Houston storm was a derecho--

an organized system of multiple repeating downbursts

that ripped across a thousand miles of Gulf Coast

from Central Texas to the Florida Panhandle.

Back in Arizona, Mike has a hunch

that the beginnings of a multi-storm system

are brewing west along interstate eight.

Oh, man, this storm!

Big towers in the air going up.

Man, this is... This looks frigging great!

Oh, my God, look at this demon!

Holy rain bombs!

Now, that's a downburst!

We have a monster rain bomb right here,

a downburst of, like, that we haven't seen so far.

I mean, this looks like a bomb went off.

That thing just collapsed right on those mountains,

and all that air is just exploding and hitting us.

This is awesome!

I could see the towers up there.

They were probably 50,000-plus.

They were kind of twisting-- even right here, I see, like,

this updraft has got a little twist to it,

and when that happens,

it's suspending that rain,

because it's rotating, so it's suspending up there more,

so then, when it comes down, it just has so much more force.

And all that air, all the stuff we're feeling,

it's just blasting from that storm,

and it's constant, because there was probably multiple downbursts

that happened-- there was, like, an initial one.

There, there was one on the right, one on the left,

and then just, like, the main thing went down,

and now we're getting this dust that's appearing right here.

The dusty outflow winds from the rain bombs are racing west,

and Mike jumps in his vehicle

to get ahead of the growing storm

and reset in a new position.

There's-- you can kind of make it out.

So, we actually have a dust storm coming.

So just overall, it's getting better as it goes west.

Oof, lightning!

This dust in there is looking good.

This dust is just food coloring in the atmosphere.

Basically, the dust and the shelf structure

are showing us the outflow, or the cold pool,

where it's all consolidated and pushing.

But without the dust, you don't get to see

what the air's actually doing.

This is gorgeous-- the color, this is what...

This is what you live for.

But this is the result

of stronger downbursts that consolidated

and just formed intense outflow.

This is amazing!

What?!

Whoa, it's making them disappear now!

What a day! What a day!

This dust storm produced winds of over 55 miles per hour.

It was the result of multiple microbursts

organizing into a larger system, creating a macroburst.

If this dust-filled cold pool had hit Phoenix

instead of the desert,

it could have caused extensive damage.

And if it had grown further, it could have become a derecho--

exactly what hit Houston.

Downbursts and derechos are dangerous

wherever they strike,

but especially so when they hit built-up areas.

So is there any way to protect against them?

Ian Giammanco is lead meteorologist

at the Insurance Institute for Business and Home Safety,

the IBHS.

His team investigates

how a downburst's devastating combination of wind and hail

inflicts damage on property.

When wind attacks a building,

it's always looking for the weakest link in that chain.

And a lot of times, that is at the edges of roofs

or if an opening,

say, a garage door, a window, a door fails,

and that air is allowed to rush in.

They use a monster wind tunnel

to test the construction standards

of North American homes:

an extraordinary array of 105 fans.

Each fan is almost six feet in diameter

and packs 350 horsepower.

Together, they can produce winds topping 100 miles per hour,

just like the Houston derecho.

Wind is a cascade of damage.

It often starts with one little thing

that cascades to the next, to the next, to the next.

And the next thing you know,

you're looking at a catastrophic failure.

To reinforce homes against the destructive power

of downburst winds,

Ian and the team at IBHS

have developed a new building standard.

It's designed to help

minimize the amount of damage

that comes with severe wind events.

The IBHS construction methods include

a hail-resistant roof,

and also adds anchors and metal connectors

to lock the roof to the walls

and the walls to the foundations,

transferring the wind's force down into the ground.

Build a home to these standards

and put it alongside a typical home,

and the difference is clear.

As our wind speeds increase,

the front door fails.

That allows wind to rush into that structure

and start pushing out.

The fortified home, however, sitting on its right,

it's structurally sound-- it can take those forces,

whereas the conventionally built home simply couldn't.

And the next thing you know, the wall has failed...

...and it comes apart.

As our atmosphere warms,

that's simply producing more fuel for thunderstorms.

It's air that wants to go up.

Those thunderstorms can take advantage of that.

In a warming world,

you can store more water vapor in the air,

so as we have more of this fuel in the air

that can then condensate and release heat,

these thunderstorms, the derechos,

can become more intense.

As the world warms,

there will be more moisture in the atmosphere on average.

But some regions could actually dry out.

Drier air has to rise farther to cool enough to condense,

so cloud bases would be higher.

That could have big consequences.

If you had a cloud base of this high

and now you raise it to this high,

you have so much dry air

to put raindrops through, to put hailstones through,

that it gives the storm system a lot more time

to evaporate and melt.

More evaporation and melting may mean

there is less precipitation hitting the ground,

but it also means faster-falling, cold, dense air.

And so there's every reason to expect, with changing climates,

stronger downbursts.

Derechos already became more powerful

over the last 40 years

because the air is warmer over the U.S. nowadays

than it was in the '80s.

So, this is a race to get our building codes

and get our structures ready to deal

with what could be the weather of the future.

Protecting homes and businesses will reduce

the financial cost of future downbursts and derechos.

And better forecasting is also essential.

But weather forecasts face limits

because of the inherently chaotic nature

of the atmosphere.

If you start a model

with slightly different initial conditions,

the end results can be very different

based on some very simple differences

in the initial information we put into our models.

We can't actually accurately predict

the weather beyond about 14 days.

By updating the model every few minutes with live data,

the forecast can be nudged back to reality.

But data quality is crucial.

And some of the best data comes from space-based instruments.

French Guiana.

An Ariane 5 rocket delivers

a 4.2-ton next-gen weather satellite

into a geostationary orbit,

where it stays positioned above Europe and North Africa.

It's one of three satellites

that will be co-located in the same orbit

to probe the region's atmosphere.

Olivier Brize is part of the team

behind this new satellite system.

The Meteosat mission is a geostationary satellite.

You have a constant and stable view of the Earth.

The aim is to improve the short-term nowcasting

and also to provide alerts on a severe weather event

on a very short term, within one or two hours

and within a very small area:

on a valley, on a village, on a town.

These satellites will provide a 3D profile

of the atmosphere above Europe and North Africa,

including humidity,

wind speed,

and temperature.

This real-time view will enable forecasters

to spot the warning signs of an atmosphere

primed to produce downbursts:

rapidly cooling cloud tops

or banks of dry air around developing thunderstorms...

...allowing forecasters to give downburst warnings.

For us working on this project, we are convinced

that we are in a position to save lives.

So far, the U.S. has

no equivalent geostationary satellite system,

but there are plans for future deployment.

If we want to save lives around the world,

we really need global observations, and so,

the best way to do this is to build satellite platforms.

We've made progress with the forecasting

of extreme downbursts and derechos,

but there's still a lot of things

that we don't know about them.

However, our modeling systems, our observational systems,

and our field campaigns

have allowed us to really move forward

with understanding these storms and better predicting them.

Earth's atmosphere is a cauldron

mixing warm, wet air with cold air above,

a mixture that generates huge thunderstorms.

And as the Earth's atmosphere warms,

it will hold more moisture and more energy to fuel them.

As we move forward with new satellite technology,

I believe that our ability to forecast these systems

will be even more improved in the next zero to ten years.

But while we wait for forecasts to catch up,

more severe winds,

more deadly hail,

and more extreme rainfall

will mean more devastating rain bombs.