Wild Weather (2014–…): Season 1, Episode 2 - Water: The Shape Shifter - full transcript

- Weather.

One of the most astonishing
forces on Earth.

Capable of both devastating power,

and spectacular beauty.

Wherever you live on the planet,
weather shapes your world.

Yet, for most of us, how
it works is a mystery.

To really understand weather,
you have to get inside it.

So I'm going to strip
weather back to basics.

All in the name of science.

Uncovering it's secrets
in a series of brave,

ambitious



and sometimes just plain
unlikely experiments.

Well, it certainly feels
like a dust storm from here.

To show you weather like
you've never seen it before.

Water lies at the heart of our weather,

but not just as rain.

Because water can transform itself,

redefining its powers in the process,

creating the fastest, the slowest,

the softest and the
hardest weather on Earth.

Often changing from one to
another with alarming speed

and striking consequences.

In this program, I'll reveal
water in all its shapes.

I'll capture a cloud,

okay little cloud, let's see what you got,



to see how just much it weighs,

discover why hailstones are
able to do so much damage.

Look at that.

Find out what would happen if rain fell

in one big lump.

It's amazing, isn't it?

And I'll experience water in its most

ferociously powerful
form, as an avalanche.

I'm speechless, genuinely speechless.

All our everyday weather
appears to come from the clouds.

They're the best clues most of us have

as to what the weather
is likely to do next.

They dictate if it's sunny or dark,

and they're where all our watery
weather seems to come from.

But how?

What exactly is a cloud?

C'mon. You've done it.

If not, you should.

Gazing at clouds. Dreaming up shapes.

And the next time you do,
two things you should know

about clouds that might just
change the way you think.

Number one, clouds are really heavy.

Even that fluffy little cumulus

could weigh as much as two elephants.

And secondly, because of that weight,

all clouds are falling,

slowly, steadily down to Earth.

I know, both those things
sound pretty unlikely,

which is why I'm going
to put them to the test.

And I'm going to start
by trying to discover

just how much a small
cloud really does weigh.

Obviously, you can't just hang
a cloud off a spring balance

or pop it on a set of scales.

But, you could measure the moisture in it

and work it out from that.

So I thought, what it we could fly

a giant ball of cotton wool into the cloud

to gather the moisture?

As an idea it needs a
bit of finessing, yes,

so I got an engineering
mate of mine to iron out

some of the wrinkles and
he came up with this.

Okay, so it's not actually cotton wool.

It's an industrial version, ceramic wool.

And it's not one solid ball, either.

My friend reckoned that by
making the center hollow,

it would double the amount of wool

that came in to contact with the cloud.

He calls it his Sky Sponge.

And then we've got that

to put it in the cloud.

It's all fairly standard stuff.

First off, let's check out much
this sky sponge weighs dry.

That's 37 kilos, which, for a sponge

is already pretty heavy.

But we need that weight to
be able to fly it accurately.

Especially when the pilot

is someone not that used
to carrying freight.

I know, I know. It's not a good start.

But as nobody has ever done
anything like this before,

I'm as good a choice as anybody.

In the end, it was deemed
not a job for an amateur,

no matter how enthusiastic,

so I took a co-pilot, Andrew,

with me to keep an eye on things,

mostly on me.

So, helicopter, check.

Basket full of highly
absorbent ceramic wool, check.

All I need now is a nice
little cloud to dip it in to.

And that's not as easy as you might think.

Because, when you get
close to them, clouds are,

well, they're enormous.

I need to fly low enough
to dip the sky sponge

into the cloud, but high enough

to keep the chopper above it.

Which is trickier than it sounds.

Well, for me.

Great. Well, that's all 'round bad.

First time 'round, I missed
the cloud altogether.

This is a fairly unusual
exercise, cloud collecting.

Yeah. That's my excuse, anyway.

This one will do, a treat.

Okay little cloud, let's see what you got.

Close up, the cloud seems so
wispy, it's hard to imagine

we're going to soak any water up at all.

Okay, we dipped it.

Let's get this thing down
and see what we've got.

Well, it's wet. That's a start.

But how wet?

Have we managed to collect enough moisture

to make a difference on the scales?

We have. 10 whole kilograms of difference.

I know that doesn't sound like much,

but look at the size of the cloud.

Then look how much of it
the sky sponge flew through.

Just that small section had
10 kilos of water in it.

If every section that
size weighs the same,

then that little cloud
must getting on for,

well, not quite nine tons,

but a lot.

And a good sized thunder cloud might be

10 kilometers tall and 10 kilometers wide,

which would make it's total weight

more like a million elephants.

Or if you prefer, about 60,000 jumbo jets.

So how on earth does all
that weight stay up there?

To find that out, we're going
to have to build a cloud.

of our own.

Right. What I've asked to achieve here

is an indoor cloud.

What I've got is a cattle
trough full of water

and I don't even know
what these things are.

Fortunately, what I've also got is Jim,

who is an atmospheric scientist
and can hopefully help.

I don't, what is this
and how's it gonna work?

- So this is how we're gonna
make something akin to clouds.

- Right.

- Obviously, it's not a cloud
but it's the closest we've got

to a cloud making machine.

So what we've got in here are
some ultrasonic humidifiers.

You quite often see these sort
of things at garden centers

and things like that.

They just produce very, very fine mist.

- Garden centers?
- Garden centers.

- It's sounding less high
tech now, I'll be honest.

- They're masquerading as
nice, ornamental devices,

but secretly they're cloud making devices.

- Well, there we go. Well, c.mon then.

Make it work.

- So, what we need to do is turn this on.

- Hello.
- There you go.

- Suddenly,
miniature clouds appear.

And that's just by breaking
the water molecules

down in to smaller bits.

- We're breaking the liquid water

into very, very tiny droplets of water.

- These garden pond devices

turn the water into tiny droplets.

And that is exactly how a cloud works.

Clouds float because the
water drops inside them

are so small and so light.

What's the difference in size?

How big is a droplet of this
compared to the droplet--

- So, a droplet of that is five microns,

but that means absolutely nothing to you.

- Small.

- But a rain droplet, you
can get your head around

the size of raindrops,
about two millimeters.

So the difference in size between
these and the rain droplet

is the same as if you got
a sugar cube and a caravan.

- Which is the caravan?

- The caravan is the rain droplet,

- Right.

- and the sugar cube is
these tiny little droplets.

- Well that is working.

The humidifiers have
split all our caravans up

in to billions of sugar cubes.

- Okay, lid goes on.

- Okay.

- But to really complete the effect,

we want to see if we can get
those tiny moisture droplets

to float in the air.

- We'll turn the fan on now,

and we'll see our clouds emerge.

- There it is.

Weirdly, it feels dry.

Hard to believe our sky sponge

managed to soak this stuff up.

So this isn't just something
that looks a bit like a cloud,

this is pretty close to a cloud.

- But these are just droplets of water,

very, very small droplets of water,

and that's what a cloud it.

- Jim, not being critical of your cloud,

but it looks a lot more frantic.

I think of clouds as
just solid state, really,

just drifting.

- What you're seeing
here, is what's happening

around the edge of a cloud.

It's constantly changing.

- So you get up close to a cloud
and it's really quite busy.

- Yes.

- So, whilst I'm very impressed
with your homemade cloud,

it's kind not up enough.

- Now, this might look like overkill,

but actually, our cattle
trough is surprisingly heavy.

Just like the water in a real cloud.

And I do need to get all
that water off the ground

to check that second fact.

Are all clouds really
falling back to earth?

Jim and I wait with baited breath.

We might have made the water
droplets small enough to float,

but, it's true.

Once they're up in the air,

they drift back towards the ground.

So this effect, I can see
it rolling over the top

and sort of falling.

That's accurate.

- Yes. Our cloud is dropping out.

If you look at clouds with binoculars

or something like that, you'll
see bits of streams of cloud.

- So because this is
small it all looks faster,

but if this were as big as a real cloud,

this effect, this exact effect,

is what's going on all the time.

- Yes. Just continuously, all the time.

'Round the edges of clouds,'round
the periphery of clouds,

you've got this process
going on all the time.

- So there you have it.

Clouds are heavy,

and they are all falling
slowly down to earth.

It's just that most evaporate
before they ever get there.

In fact, the typical lifespan
of a small cumulus cloud

is only 10-15 minutes.

But while they're up there,
they act as a sort of

public transport system for water,

carrying it from one place to another.

Until either the service goes off duty

or they dump all their passengers out,

as rain.

There are about 13 trillion tons of water

being moved around in the atmosphere.

And every day, about a tenth of that comes

crashing back down to earth.

Sometimes these storms
are incredibly intense.

The quickest on record dumped
12 centimeters of water

in just eight minutes.

The heaviest managed nearly
a meter and a half of rain

in under 10 hours.

But how does moisture
actually turn in to rain?

We can't look in to a cloud
to see how raindrops form,

but we can get an idea of what's going on

by looking in a puddle.

As the raindrop hits, part of
it is attracted to the water.

What bounces back up is a smaller droplet,

about half the size.

When that droplet hits, the
same thing happens again.

Around half of it stays in the puddle.

Now, imagine that in
reverse and upside down.

The puddle is the cloud.

Our water droplet doubles in size

by attracting other water droplets.

These stick on in a process
scientists call coalescence.

It increases again and again

until it's so heavy,

it falls away.

And that is, roughly, how rain is formed.

But how heavy can rain really get?

We talk about heavy rain,

but water is heavy.

To show how heavy, we're
going to fill the bucket

of this digger up with
water to see what a big lump

of rain would actually do.

So we have four cubic meters
of water in the bucket,

which amounts to four tons at height.

Then beneath it you'll
see we've found a car,

for scientific purposes.

Let's see just how much damage
that amount of water can do.

Looks like rain.

Yeah, pretty brutal.

But I shouldn't be surprised.

Because the water actually
weighed four times more

than the car underneath it.

Every minute of every day,

nine hundred million tons
of rain land on our planet.

Luckily, this could never
happen with real rain.

Not even in a tropical storm,
where sometimes it feels

that the heavens have literally opened.

Partly because, as we saw earlier,

raindrops form the moment
they get heavy enough.

And partly because of what
happens to rain as it falls.

To show you what I mean, I'm hard at work

building a sand castle.

And professor Jane Rickson
from Cranfield University

is filling a plastic bucket from a pond.

There were always kids like you
on the beach, weren't there?

Okay, so what's all this about.

Well, pour water on a sandcastle

and you completely flatten it.

No surprises there.

But rain doesn't fall from waist height

It falls from clouds that
are at least 300 meters

above the ground.

And that makes all the difference.

Let me show you by building
another sandcastle.

I'm throwing the water off something

just a little bit higher.

Now, obviously,

this isn't as high as real cloud.

They start at around 300 meters.

This tower is 30, but it's tall
enough for what we wanna do.

- Okay, Richard, let it go.

- Idiot.

- Yeah. Wrong side.

How was I to know?

Let's try it again.

- Okay, Richard. Let it fall.

- And so, another bucket
full leaves the tower

but what arrives below is rain.

And there it is, still standing.

So, why? Why is it if I throw
the water from up there,

you'd think it would smash
it to bits even more,

but it's still standing.

What's the difference?

- Well, what happens as you
were throwing that water down,

air resistance, the turbulence in the air,

is overcoming the surface
tension of that lump of water,

breaking it into smaller drops.

Do you want to go and
see that, to do it again?

- Yes. I'll get the water.

As the water falls, it
meets air resistance.

And the larger the lump of water,

the more resistance it experiences.

That friction breaks the
water up into smaller pieces,

sometimes inflating the
drops like parachutes

before blowing them apart.

The further they fall, the
smaller those drops become,

until finally, they're so small

that the air has little
effect on them and they land

as rain.

So that's why the water landed in drops

and didn't smash it, rather
than a big bucket-shaped lump.

- That's right.

And in fact, you can
actually see the point

at which that lump starts to break up

into those smaller drops.

- Well, you can if I
climb the tower again.

It actually happens surprisingly quickly.

Within 10 meters, there's
enough air blowing

on our bucket full of water
to break it down into drops.

If our digger had been
just a few meters higher,

then the car might well have survived.

So even if it was possible for
water to fall out of the sky

in one big lump, by the
time it got to the ground.

it would still be rain.

Because they break down like this,

the average raindrop ends up
about two millimeters across.

But there is a way the water
can fall out of the air

in bigger, more dangerous pieces.

By shape shifting in to ice.

Now, most of us think that when we see ice

falling out of the sky, it's hail.

So what if I told you
this wasn't hail at all.

Sure, it looks like hail,
but it can't be hail.

You can't get hail in winter.

It only happens in summer.

I know, you think you've
seen hail in winter,

but trust me, you haven't.

What you've seen is this.

Ice pellet.

Ice pellets are formed when a snowflake

partially melts on the way down,

losing all its pretty
branches and then refreezes,

forming a small ball
before it hits the ground.

Just to make things even more confusing,

in North America, they call this sleet,

which over here means a sort
of slushy mix of rain and snow.

Either way, this is not hail.

Hail is something entirely different.

Charles Knight has been
studying hailstones

for the last 50 years,

and in his refrigerated
laboratory in Boulder, Colorado,

he offers to show me exactly how

hailstones are different
by sawing one in half.

- It's very simple.

This is an example of, really,

what you would call a giant hailstone.

- It's enormous.

- It's enormous, yes.

- But that's obviously
not going to stop him

cutting it in half,

even though this
hailstone is 15 years old.

Wow.

You can clearly see the layers
the hailstone is made of.

- If you make a thin section,

then you can really see the layering.

- That's a slice right through.

That's absolutely beautiful.

That's really telling
its own story, isn't it?

Just like the rings of a tree,

these layers chart the story
of how this hailstone grew.

It's a story that starts with a thunderstorm.

And thunderstorms only
tend to happen in summer.

Because of the height of thunder clouds,

some of the water droplets
inside them freeze.

But the powerful updrafts
created by the warm weather

keep the droplets supported in the cloud,

where they collect more water,

with new layers freezing
on in a separate shell.

Until finally, there are so many layers

that they're too heavy to be supported

and they fall to the ground.

Certainly hail is powerful.

It causes over a billion
pounds worth of damage a year.

But is it any harder
than conventional ice?

To find out, we're gonna have
to go into uncharted territory

with an experiment that
hasn't been done before,

using that.

Yeah, I know, it looks like
a length of plastic pipe

on some tables in a field, and
to some extent, well, it is.

But you should see what it's about to do

to that table tennis bat.

Its inventors, Purdue University's

Jim Stratton and Craig Zehrung,

wanted to see just how fast they could get

an ordinary ping pong ball to fly.

And the answer, using this contraption,

turns out to be very fast indeed.

That is astonishing.

This projectile is moving
when it comes out of there.

- Yeah.

- About 919 miles an hour.

- That's brisk, isn't it.

- So you brought along your device,

which is, if you think about it,

a sort of nightmarish
automatic serving machine,

and you've agreed to help us.

- Yeah.
- Yeah.

- Okay,right. So here's the plan.

We're gonna see which is harder,

ice or hail.

But first of all, we've
gotta make some hailstones.

We've already seen how
much of a faff that is,

even for Mother Nature.

But luckily, Jim and Craig have a plan.

A plan that starts with dry ice.

It's like an 80's pop video.

A pop video starring

a bead on a bit of string.

The dry ice makes the
bead really, really cold.

Two rolls.

- Yep.
- Yep.

- Before it's dropped into cold water.

- You'll notice every
time he puts it in there,

you can hear just a little bit of a crack,

you can hear a little bit of
a fizz, and that's the water

instantaneously freezing to the outside.

- So that's one layer of
ice 'round that little --

- A very small area, yep

- A very small area.

- How long does this take?

- About 10 minutes.

- God.

- How many of these do we need.

- Quite a few.

And they need to be the
size of ping pong balls

to fire them from Jim and Craig's gun.

Can I have a go?

- Yep.
- Go.

- Right. Dip it in here,

fairly quickly into there.

That's it. Look at that.

It's already the size of a pea.

I'm just suggesting

we probably need to find a
way of mass-producing these.

I mean, this is the land of Henry Ford.

- Right.

- One is good. We can try three.

- And now you've tripled your efficiency.

- Haven't I. Haven't I.

Sometimes on TV we don't
do things in actual time.

This is one of those occasions.

- You gonna do anything?

- I'm reading this.

- There's no words, You're
just looking at the pictures.

- My turn again?

- Yes.

- Hoo, you've been busy.

- Hail's ready.

- So we have something
to compare them with.

We've also frozen some
water into ordinary ice,

using a few of Craig and
Jim's spare ping pong balls

as molds.

So we've got solid ice and we've got hail,

which is ice in layers.

Time to put them up against each other

to see if there really is a difference.

And we can't resist starting with

one of our homemade hailstones.

- I'll give you the honors.

Alls you have to do is puncture.

- Let's scoot back a little
bit so we can look at--

- Why is everyone else standing back?

- We're getting so we can see.

- Right.

What? I've not done this before, have I?

How wrong can it go?

Are we ready?

- Yep.
- We're ready.

- Punching a hole in there now.

It's quite dramatic as it turns out.

Yeah, let's have a look at the footage.

Believe it or not, we're breaking

new scientific ground here.

So to make sure we capture any differences

between the ice and the hail,

we're recording everything
at ultra high speed.

And sure enough, our cameras
capture every detail,

from the plastic seal popping off the tube

to our hurtling hailstone
punching through the target.

- Hoo, hoo, look at that.

- That is awesome.

- Beautiful.

- So here's the set up.

We've got lots of different sorts of wood,

and we're going to take
two shots at each piece.

First, with plain ice, then
with our homemade hail.

First up, chip board. Right.

- Three, two, one.

- Ice, straight through.

Hail, straight through.

Okay, slightly thicker
piece of chip board.

Same result.

Plywood.

The ice barely dents it.

C'mon, hail.

- Three, two, one.

- Well, there is a difference.

The hail splintered the
back of the plywood.

Let's try a slightly thinner piece.

This time, the ice
barely makes it through.

The hole it makes is far smaller

than the projectile itself.

Right, fingers crossed.

- Nice.

- That's awesome.

- Did it work? What happened?

- It did.

- It smashed, and there's your impact.

- Yeah, well that's right the way through.

That's completely different.

Same piece of wood,

same shooting speed,

different results.

In slowmo, you can clearly
see how much of the iceball

never makes it through the board.

Well, it might be crude but
that is what I hoped we'd see.

This mark here, that's
from the straight ice

barely getting through.

That is our homemade hail
with its laminated layers

around it, clearly a
more fearsome projectile.

Both balls are made of frozen water,

so you wouldn't expect any
difference in how hard they are.

But the layers in hail do
appear to make it stronger.

So summer hail does seem to be harder

than winter ice.

But water can shape shift

into something even more dangerous.

Naturally quicker than hail.

With a mightier punch than hail.

And what it is might well surprise you.

This is how most of us are
used to seeing snow move.

Delicate flakes floating
gently down to earth.

Floating so gently, that a
snowflake can take nearly an hour

before it finally reaches the ground.

Traveling at just four miles an hour,

little more than walking speed.

And yet snow can be the
fastest form of water

that there is.

Because when it's in an avalanche,

it can hit 80 miles an
hour in six seconds flat.

And then, well, it just
keeps on accelerating.

The fastest one ever recorded,

on Mount St. Helens in America,

clocked a staggering 250 miles an hour.

So how can snow move down a mountain

faster than water can.

Walter Steinkogler of
the Institute for Snow

and Avalanche Research
is trying to find out

how that incredible speed is possible

by starting an avalanche of his own.

Walter.

- Yes.

- Is this where it's gonna happen.

- Absolutely, You can
see quite nicely now.

Just the whole slope.

You see two spontaneous avalanches already

and we gonna try to release
avalanches from the very top.

- Well, don't those two avalanches mean

it's already happened, it's all over.

- No, no, no, not at all.

You see there's plenty of
snow still on the slope?

- And actually this is a
very good indicator for us

that there is the potential
to produce nice avalanche.

- And then when that's
going on, you're going to be

conducting experiments and
learning them, and this is

part of an ongoing piece
of work for you, isn't it?

- It is. It is actually
part of my PhD thesis

and this data is really
essential for my work, yes.

- Right.

There are several different
types of avalanche.

But the fastest, by far, is what's known

as a dry powder avalanche.

And that's the type we're hoping to get.

If he can trigger a dry powder avalanche,

Walter can find out more
about how they move so fast.

And we've offered to
help, by putting a barrage

of slow motion cameras on the slope.

We're not gonna mess up your PhD.

- I will tell you afterwards,
but I would appreciate

if you don't do that.

- I won't. If I do, send him the bill.

- Send to this guy?

- Yes.

- Perfect. I will.

- He's in charge. I'm not.

Let's hope it doesn't come to that.

But I would like to add an extra element

into his experiment.

So Walter, can I place these on the slope.

If they're a known distance apart,

I thought I could time
when the front, the head,

- We call it the front of the avalanche

- passes one of these, I can
time it over that distance

and I can work out how fast it's going.

- Sure, sure. That's a nice approach.

You can do that.

- Thank you very much.

Right. We'll do it.

I just need a helicopter.

Okay, well that's that sorted.

But now we need to work out
how to fly our fences into

precise positions without
triggering an avalanche ourselves.

Our safety team have been
thinking long and hard

about the best way to do it.

And what they've come up

is dangling someone on a bit of rope.

This someone, in fact, who apparently

enjoys this kind of thing.

That is the single coolest
thing I have ever witnessed.

That man is, without a doubt,

the best helicopter pilot
I've ever seen in action.

I mean, that sky sponge
was difficult enough.

Just to be flying that
close to mountains and sheer

rock faces in this gusty,
windy, changeable weather.

Just that, let alone with
another bloke dangling

from a piece of rope below you,

and then below that a huge,
well basically, wooden sail.

I'm speechless, genuinely speechless.

Walter has told us where he
expects the avalanche to fall,

so we position the first
fence slap bang in its path.

But the conditions up
here are very changeable,

as we discover when we try
to fly the second fence in.

Suddenly the winds quicken

and start to gust alarmingly.

At any moment, the whole fence could be

dashed into the side of the mountain,

taking that bloke with it,

not to mention the helicopter.

And the fence needs to
be exactly 100 meters

from the first one.

Never have the words "Rather him that me,"

been more directly applicable.

All I have to do now

is wait for them to trigger the avalanche.

That was the explosives.

Okay, we're off.

Fence one. Fence...

Well, my boards have gone.

I missed it.

But I suppose it does prove, in a way,

just how fast an avalanche can be.

And luckily for me,
our slow motion cameras

captured everything.

So let's take a look at
that avalanche again.

This is the moment the dynamite is

dropped from the helicopter,

causing this explosion

at the top of the mountain.

Immediately it's surrounded
by a powder cloud,

made up of one percent

and 99 percent air.

This is a dry powder avalanche.

The avalanche accelerates
down the steep incline

until it reaches our first fence,

but not exactly at the angle we expected.

The leading edge passes the first one now.

And that particular bit of
snow reaches the second fence,

now.

Almost exactly the same time
the first fence is destroyed.

No wonder I had trouble timing it.

Our avalanche was
actually only traveling at

25 miles an hour,

just a tenth of the speed of
the fastest one ever measured,

but still faster

than if we'd just pushed
that snow over a cliff.

I want to know how that's possible.

Let's imagine, so there's
a chunk of snow at the top,

and then it starts to move.

What's happening to that snow

from the moment it starts to move down?

- Well first, it will break
into pieces and it gets

rounded a bit, and it
also gets compressed.

- And these are the pieces
which you can see up there.

They look like snowballs.

- Technically, most of
them are snowballs, yes.

- These snowballs are the
secret of what's going on

underneath that powder cloud.

Walter offers to show me how.

Okay, Walter, this is
like an avalanche how?

- Well, you imagine an avalanche
that's moving down a slope,

it's gonna pick up snow,
like you are doing now,

and it's gonna put it in
motion as in our tumbler here.

It seems you're losing your motivation.

Come on, keep on going.
One more, you can do it.

You can do it. Come on, Richard.

Perfect. I think we are good there.

And you can see already, it's compacting,

that it's breaking apart again,

that it's compacting
again, and at some point

you will end up with ball-shaped features.

- It is magically making--
- Snowballs.

- a cement mixer full of snowballs, yeah.

- It makes snowballs.

Of course, in an avalanche
this is happening much faster

and it's much more violent
process going on there.

- This is a slowed down version
of exactly the same process,

and you can see that sort
of grinding, rolling motion

you can imagine happening.

- Perfect. That's exactly the case.

Yeah, yeah, true.

- So understanding this will
allow you understand more about

how fast it might go, where it
might go, how it will behave.

- Absolutely.

I would say they are quite done.

- Can I turn it off?

- Yeah, turn it off, please.

- So in here, snowballs.

- Perfect snowballs, right, aren't they?

- I mean that's seriously packed.

- It's quite hard, right.

It would be not that nice
to throw it on a person,

I guess, this one.

- Put something on wheels,
and it can accelerate

quicker than if you simply drop it.

And these snowballs may be the wheels

of a dry powder avalanche.

Snow is the softest, lightest way

that water can fall to earth,

but an avalanche can move

faster than any other type of water.

Four times faster than the
fastest flash flood ever measured

and it seems snowballs
might well be the secret.

Of all the water on our blue planet,

only a tiny fraction is
actually in the atmosphere.

Yet water's incredible
powers of transformation

mean that that's enough to
bring us all our clouds,

rain, hail and snow.

And with it, all the
everyday weather on Earth.

In the final episode, I
investigate the one thing

that drives all our weather.

Temperature.

I discover how you can
be struck by lightning,

but you can also be hit by thunder.

Ho.

I witness the mystery of an ice storm.

This is strangely addictive.

And I start my very own dust storm,

hope I don't trigger an
international incident,

to find out how it's
possible for sound to travel

half way 'round the globe.

Seriously, it's gone.