Wild Weather

[THUNDER] NARRATOR: WEATHER... ONE OF THE MOST ASTONISHING FORCES ON EARTH, CAPABLE OF BOTH DEVASTATING POWER AND SPECTACULAR BEAUTY.

WHEREVER YOU ARE ON THE PLANET, WEATHER SHAPES YOUR WORLD.

YET FOR MOST OF US, HOW IT WORKS IS A MYSTERY... ITS SECRETS HIDDEN OUT OF VIEW.

TO REALLY UNDERSTAND HOW WEATHER WORKS, YOU NEED TO GET INSIDE IT, UNCOVERING ITS SECRETS IN A SERIES OF AMBITIOUS AND REVEALING EXPERIMENTS... THAT SHOW WEATHER AS IT'S NEVER BEEN SEEN BEFORE.

NARRATOR: ALL WEATHER, NO MATTER HOW RARE OR HOW UNUSUAL, CAN BE BROKEN DOWN INTO 3 SIMPLE INGREDIENTS: WIND... WATER... AND TEMPERATURE.

BY COMBINING THOSE 3 ELEMENTS IN DIFFERENT AMOUNTS, IT'S POSSIBLE TO CREATE ANY TYPE OF WEATHER AT ALL.

SOME OF THESE COMBINATIONS MAKE PERFECT SENSE.

MIXING RAIN AND WIND CREATES A TEMPEST.

MIXING TEMPERATURE AND RAIN MAKES ICE.

BUT THERE ARE MANY THAT ARE MORE SURPRISING.

TAKE INTENSE HEAT, ADD A STRONG WIND, AND YOU CAN HELP CREATE RAIN.

HERE'S HOW IT WORKS.

TAKE ONE DESERT, AN AREA FAR FROM WATER THAT HAS BEEN DRIED OUT BY THE HEAT OF THE SUN.

THEN ADD A POWERFUL WIND, CAPABLE OF BLOWING LOOSE SAND AND DIRT FROM THE DRY SURFACE.

THE WIND WHIPS THE DUST UP INTO THE AIR, AND EVENTUALLY IT FINDS ITS WAY INTO THE CLOUDS, WHERE WATER VAPOR CLINGS ON TO IT AND STARTS TO FORM RAINDROPS.

WATER, WIND, AND TEMPERATURE WORKING TOGETHER.

BUT IT'S NOT QUITE AS SIMPLE AS THAT.

THEY MIGHT SEEM POWERFUL, BUT THE AVERAGE DUST CLOUD ONLY TRAVELS BETWEEN 40 AND 80 KILOMETERS BEFORE IT DIES OUT.

SO HOW DOES DESERT DUST SEED RAIN THOUSANDS OF KILOMETERS AWAY FROM ANY DESERT?

THE SECRET IS HIDDEN AWAY INSIDE... AND THE ONLY WAY FOR SCIENTISTS TO SEE IT IS FOR THEM TO CREATE A DUST STORM.

BUT AS DR. CRAIG STRONG OF THE AUSTRALIAN NATIONAL UNIVERSITY EXPLAINS, THAT TAKES A VERY SPECIAL SORT OF ENVIRONMENT.

CRAIG: I'M LOOKING FOR THE LANDSCAPE THAT'S GOING TO PRODUCE DUST, AND I THINK THIS STONY PLAIN IS PROBABLY REALLY GOOD, BECAUSE YOU CAN SEE THESE ROCKS.

THEY'RE ACTING AS A TRAP FOR DUST.

SO I THINK IF WE DIG DOWN, WE'LL FIND THAT THERE'S PLENTY OF DUST.

IT'S JUST THAT MEANS IT HASN'T BLOWN AWAY YET BECAUSE THE ROCKS ARE LOCKING ALL THAT DUST IN.

AND ONCE WE GET UNDER THERE, IT'S JUST DUST GOLD.

YOU KNOW, LOOK AT THIS.

THE ROCKS ARE DOING THE JOB OF PROTECTING THE SOIL, SO I RECKON WE P--PROBABLY SHOULD PICK UP THE ROCKS AND MOVE THEM OUT OF THE WAY.

THAT'S THE FIRST STEP.

NARRATOR: BY SCRAPING AWAY THE ROCKS FROM THIS STONY PLAIN, CRAIG HOPES TO GET ALL THAT DUST OUT IN THE OPEN.

MEANWHILE, A SECOND TEAM, FROM MONASH UNIVERSITY, ARE WORKING ON STEP TWO-- ASSEMBLING AN INFLATABLE TO HELP THEM MEASURE THE DUST ONCE IT'S UP IN THE AIR.

MAN: THAT'S IT.

BEAUTIFUL.

SO THE STRING GOES UP THROUGH HERE, AROUND THERE, AND THEN THIS WILL SIT ON THE KITE--OR BALLOON, STRING, AND THEN WE CAN SAMPLE INTO THE WIND NO MATTER WHAT.

NARRATOR: THESE DUST-COLLECTING SAMPLERS ARE BEING ATTACHED AT VARIOUS HEIGHTS UNDER THE BALLOON.

THE FIRST AT 3 METERS, THE SECOND AT 8 METERS, AND THE THIRD AT 20 METERS.

AN EXTRA VANE AT THE TOP CARRIES A MINIATURE CAMERA TO KEEP A CLOSE EYE ON WHAT'S GOING ON.

SO CRAIG HAS GOT DUST, AND HE'S GOT A WAY TO TRACK WHERE THAT DUST GOES.

NOW HE JUST NEEDS TO INTRODUCE SOME WIND... AND GET THIS DUST STORM STARTED.

WHAT'S REMARKABLE IS HOW MUCH ENERGY THAT TAKES.

THE SCIENTISTS ARE HAVING TO USE CARS, FANS, SHOVELERS, AND BLOWERS TO TRY AND GET THE DUST OFF THE GROUND.

THIS WHOLE EXPERIMENT IS TINY COMPARED TO A REAL DUST STORM, BUT THE PRINCIPLES ARE JUST THE SAME.

THE VEHICLES AND THE BLOWERS DO THE JOB OF THE WIND, WHIPPING THAT DUST UP OFF THE GROUND.

THERE'S NO WAY THAT THEY CAN BLOW IT HIGHER THAN 5 OR 6 METERS.

BUT INSIDE THE DUST STORM, A HIDDEN PROCESS IS STARTING TO TAKE PLACE.

INDIVIDUAL GRAINS ARE COLLIDING AGAINST EACH OTHER... [POPPING] PROPELLING THE SMALLER PIECES HIGH INTO THE AIR.

THE DUST PARTICLES AREN'T MERELY BEING BLOWN ABOUT.

THEY'RE BOUNCING.

THE KINETIC ENERGY FROM ONE PARTICLE IS TRANSFERRED TO ANOTHER, CAUSING THE SMALLER PIECE OF DUST TO SHOOT SKYWARDS, HOPEFULLY ALL THE WAY UP TO THE HIGHEST SAMPLER ON THE BALLOON.

BUT THERE'S ONLY ONE WAY TO KNOW FOR SURE: CHECK WHAT'S IN THOSE PUMPS.

LUCKILY, DR. NIGEL TAPPER HAS A MAKESHIFT LABORATORY RIGHT ON SITE.

NIGEL: SO HERE WE HAVE THE LOWER LEVEL, MID-LEVEL, 8 METERS, UPPER LEVEL, AROUND 20 METERS.

OK.

SO WE'LL START WITH THE ONE CLOSEST TO THE SURFACE, AND, UH, WE'LL CRANK THIS OPEN, SHALL WE?

HERE WE GO.

SO WE'VE ACTUALLY GOT QUITE A BIT OF MATERIAL ON THERE.

YOU CAN SEE PLENTY OF--OF DUST IN THAT FINE MATERIAL.

BUT LET'S NOW HAVE A LOOK AT THE MID-LEVEL.

HERE WE GO.

SO WE'VE ACTUALLY GOT A BIT OF FINE MATERIAL AT 8 METERS.

SO, IT WILL BE INTERESTING TO SEE IF WE'VE ACTUALLY GOT MATERIAL AT 20 METERS, AND IF WE DO, IT'LL BE A TRIBUTE TO OUR, UH--OUR DUST-MAKING ACTIVITIES.

WELL, LOOK.

SURPRISINGLY, THERE IS A LITTLE BIT THERE.

I'M QUITE IMPRESSED WITH WHAT WE WERE ABLE TO SEE, ACTUALLY, AND, UH--AND I'M REALLY IMPRESSED THAT WE WERE ABLE TO GET THE DUST THAT FAR UP.

[POPPING] NARRATOR: SO, BOUNCING IS THE SECRET MECHANISM THAT GETS DUST HIGH UP INTO THE ATMOSPHERE.

A LARGE DUST STORM CAN MOVE 15 MILLION TONS OF SAND IN A SINGLE GO.

AND WHEN THAT DUST HAS BOUNCED HIGH ENOUGH, IT GETS CAUGHT IN GLOBAL WIND PATTERNS, WHICH MOVE IT AROUND THE PLANET.

AND THAT IS HOW IT TRAVELS SO FAR FROM WHERE IT STARTED.

EVENTUALLY, SOME OF THAT DUST FINDS ITSELF IN A RAIN CLOUD, WHERE TEMPERATURE AND WATER COMBINE TO FORM WATER VAPOR.

BUT HOW DO THOSE WATER DROPLETS COME TOGETHER?

WELL, IT'S IMPRACTICAL TO LOOK INTO A CLOUD TO FIND OUT.

BUT IT IS POSSIBLE TO 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.

A WATER DROPLET DOUBLES IN SIZE BY ATTRACTING OTHER WATER DROPLETS TO THE TINY SEED OF DUST.

THESE STICK ON IN A PROCESS SCIENTISTS CALL COALESCENCE.

IT INCREASES AGAIN AND AGAIN, UNTIL IT'S SO HEAVY...

IT FALLS AWAY.

SO DOWN THE DUST COMES, CARRIED IN ITS OWN LITTLE WATER DROP, OUT OF THE SKY AND ONTO THE GROUND.

AND THAT IS BASICALLY HOW RAIN IS FORMED.

THERE ARE ABOUT 13 TRILLION TONS OF WATER BEING MOVED AROUND IN THE ATMOSPHERE, AND EVERY DAY, TEMPERATURE AND WIND CAUSE 1/10 OF THAT TO COME CRASHING BACK DOWN TO EARTH.

[WIND HOWLING] SOMETIMES THESE STORMS ARE INCREDIBLY INTENSE.

THE QUICKEST ON RECORD DUMPED 12 CENTIMETERS OF WATER IN JUST 8 MINUTES.

THE HEAVIEST MANAGED NEARLY 4 METERS IN 72 HOURS.

TO GIVE SOME IDEA OF JUST HOW HEAVY THAT IS, THIS BUCKET IS BEING FILLED UP WITH WATER TO A DEPTH OF 4 METERS.

IT'S THEN GOING TO BE DROPPED ONTO AN AREA THE SIZE OF THIS CAR.

4 CUBIC METERS OF WATER ACTUALLY WEIGHS 4 TONS... 4 TIMES HEAVIER THAN THE CAR UNDERNEATH IT.

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 RAINDROPS FALL THE MOMENT THEY GET HEAVY ENOUGH... AND PARTLY BECAUSE THEY ARE FALLING FROM SUCH A GREAT HEIGHT.

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 ARE SO SMALL THAT THE AIR HAS LITTLE EFFECT ON THEM, AND THEY LAND AS RAIN.

IF THAT DIGGER HAD BEEN JUST A FEW METERS HIGHER... THEN THE CAR MIGHT WELL HAVE SURVIVED.

BECAUSE THEY BREAK DOWN LIKE THIS, THE AVERAGE RAINDROP ENDS UP MEASURING ABOUT TWO MILLIMETERS ACROSS.

AIR RESISTANCE AND FRICTION PREVENT THEM GETTING MUCH BIGGER THAN THAT.

SO DESPITE WATER'S HEAVY WEIGHT, ANY DAMAGE RAIN CAUSES IS NOT DOWN TO THE FORCE OF IMPACT.

BUT ADD A VARIATION IN TEMPERATURE, AND ALL THAT CAN CHANGE.

THIS PROCESS USUALLY HAPPENS IN THUNDERCLOUDS... [THUNDER] BECAUSE THEY ARE MUCH HIGHER AND THEREFORE COLDER THAN NORMAL CLOUDS.

THAT DROP IN TEMPERATURE CAUSES SOME OF THE WATER DROPLETS INSIDE THE CLOUDS TO FREEZE.

THE HEAVY ICE CRYSTALS ARE HELD ALOFT, SUPPORTED BY THE RISING AIR, COLLECTING MORE AND MORE WATER AROUND THEM... WITH EACH NEW LAYER FREEZING ON IN A SEPARATE SHELL... UNTIL EVENTUALLY THERE ARE SO MANY LAYERS THAT THE BALLS OF ICE ARE JUST TOO HEAVY TO BE SUPPORTED, AND THEY FALL TO THE GROUND AS HAIL.

SUDDENLY, IMPACT IS AN ISSUE.

HAIL CAUSES OVER A BILLION DOLLARS WORTH OF DAMAGE A YEAR IN THE UNITED STATES ALONE.

BUT IS HAIL SO DESTRUCTIVE JUST BECAUSE IT'S FROZEN OR BECAUSE OF THE UNIQUE WAY THAT IT'S FORMED?

SOLVING THAT RIDDLE REQUIRES A VERY UNUSUAL PIECE OF APPARATUS.

ITS INVENTORS, ENGINEERS JIM STRATTON AND CRAIG ZEHRUNG FROM PURDUE UNIVERSITY HAD A BET TO SEE JUST HOW FAST THEY COULD GET AN ORDINARY PING-PONG BALL TO FLY, BY FIRING HAILSTONES INSTEAD OF PING-PONG BALLS, IT MIGHT BE POSSIBLE TO TEST WHETHER THE LAYERED ICE IN HAIL IS HARDER THAN ORDINARY ICE.

BUT FIRST, JIM AND CRAIG NEED TO CREATE SOME HAILSTONES.

INSTEAD OF A SPECK OF DUST, THEY ARE USING THIS SMALL PLASTIC BEAD TO ACT AS THE SEED THAT STARTS THE HAILSTONE GROWING.

THE BEAD IS DIPPED INTO DRY ICE TO LOWER ITS TEMPERATURE DRAMATICALLY.

THEN IT'S PLUNGED INTO COLD WATER.

IMMEDIATELY, A THIN LAYER OF ICE FREEZES ONTO THE SURFACE.

THE BEAD IS REMOVED AND THE WHOLE PROCESS IS REPEATED.

IT TAKES JIM AND CRAIG 10 MINUTES OF PATIENT DIPPING, BUT FINALLY THEIR HOMEMADE HAIL IS BIG ENOUGH TO FIRE FROM THE BARREL OF THEIR MACHINE.

THEY ARE DONE.

NARRATOR: SO THEY CAN COMPARE HAIL TO ORDINARY ICE, JIM AND CRAIG HAVE ALSO FROZEN PLAIN WATER, USING A FEW OF THEIR SPARE PING-PONG BALLS AS MOLDS.

THE TWO ENGINEERS HAVE GOT LOTS OF DIFFERENT SORTS OF WOOD, AND THEY'RE GOING TO TAKE TWO SHOTS AT EACH PIECE, FIRST WITH PLAIN ICE, THEN WITH THEIR HOMEMADE HAIL.

THE FIRST TARGET IS CHIPBOARD.

3, 2, 1!

NARRATOR: THE ICE...

GOES STRAIGHT THROUGH... AS DOES THE HAIL.

SO THEY TRY A SLIGHTLY THICKER PIECE OF CHIPBOARD.

THE RESULTS ARE THE SAME.

NEXT, PLYWOOD.

THE ICE BARELY DENTS IT.

WILL HAIL BE ANY STRONGER?

3, 2, 1!

NARRATOR: WELL, THERE IS A DIFFERENCE.

THE HAIL HAS SPLINTERED THE BACK OF THE PLYWOOD.

THEY DECIDE TO TRY A SLIGHTLY THINNER PIECE.

THIS TIME, THE ICE HARDLY MAKES IT THROUGH.

THE HOLE IT MAKES IS FAR SMALLER THAN THE PROJECTILE ITSELF.

CAN HAIL SUCCEED WHERE THE ICE PELLET FAILED?

WHOO!

NICE.

IT WAS AWESOME.

NARRATOR: IT DOES.

SO ALTHOUGH THEY'RE BOTH MADE FROM FROZEN WATER, IT DOES APPEAR THAT THE LAYERS IN HAIL MAKE IT MEASURABLY STRONGER.

THAT INFORMATION COULD BE INVALUABLE IN HELPING SCIENTISTS DESIGN BETTER PROTECTION FOR AIRCRAFT AND BUILDINGS EXPOSED TO HAIL'S DESTRUCTIVE POWER.

BUT TEMPERATURE CAN CAUSE WATER TO CHANGE INTO SOMETHING EVEN MORE DANGEROUS...

NATURALLY QUICKER THAN HAIL, WITH A MIGHTIER PUNCH THAN HAIL, AND WHAT IT IS MIGHT WELL SURPRISE YOU.

IT'S SNOW.

THIS IS HOW MOST PEOPLE 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.

IT TRAVELS AT JUST 6 1/2 KILOMETERS AN HOUR-- LITTLE MORE THAN WALKING SPEED.

AND YET SNOW CAN BE THE FASTEST AND ARGUABLY MOST DANGEROUS FORM OF WATER THAT THERE IS... [RUMBLING AND CRACKING] BECAUSE WHEN IT'S MOVING IN AN AVALANCHE, SNOW CAN REACH 130 KILOMETERS AN HOUR IN 6 SECONDS FLAT, AND THEN IT JUST KEEPS ON ACCELERATING.

THE FASTEST ONE EVER RECORDED, ON MOUNT ST. HELENS IN AMERICA, CLOCKED A STAGGERING 400 KILOMETERS AN HOUR.

BUT HOW IS IT POSSIBLE THAT SNOW CAN MOVE DOWN A MOUNTAIN FASTER THAN WATER CAN?

WALTER STEINKOGLER OF THE INSTITUTE FOR SNOW AND AVALANCHE RESEARCH IS TRYING TO FIND OUT.

HE AIMS TO EXAMINE THE MOVEMENT OF AN AVALANCHE BY STARTING ONE OF HIS OWN.

WALTER HAS ALREADY FOUND A SUITABLE SLOPE, AND HE AND HIS TEAM HAVE EQUIPPED IT WITH INSTRUMENTS, SENSORS, AND SLOW-MOTION CAMERAS.

NOW HE IS JUST WAITING FOR A GAP IN THE WEATHER.

WALTER: SO THE DEAL IS AT THE MOMENT THAT THE HELICOPTER WOULD BE READY TO START AT THE BA--HELI BASE, READY TO GO, BUT NOW WE ARE WAITING, AS YOU CAN SEE, THAT THE WEATHER CLEARS A BIT MORE.

THERE IS SOME BLUE SKY OVER THERE, BUT IT'S COMING AND GOING, MOVING IN, MOVING OUT, SO WE'RE JUST WAITING FOR THE WEATHER, UH, TO BRING THE HELICOPTER IN.

YES.

NARRATOR: EVEN THOUGH WALTER IS CREATING A WEATHER EVENT, THE REAL WEATHER STILL HAS TO BE RIGHT.

30 MINUTES LATER, HE GETS HIS WINDOW.

HE NEEDS THE HELICOPTER TO FLY THESE FENCES UP ONTO THE SLOPE.

BY PLACING THEM AN EXACT DISTANCE APART, THE TEAM SHOULD BE ABLE TO TIME HOW LONG IT TAKES THE AVALANCHE TO TRAVEL BETWEEN THEM.

THAT WAY, THEY CAN WORK OUT ITS SPEED.

WALTER HAS ALREADY PREDICTED WHERE HE EXPECTS THE AVALANCHE TO FALL, SO THE FIRST FENCE IS POSITIONED RIGHT IN ITS PATH.

THE SECOND IS POSITIONED EXACTLY 100 METERS BEHIND HIM.

MORE THAN THIS, AND THE AVALANCHE MIGHT MISS IT.

ANY NEARER AND THE DISTANCE WILL BE TOO SHORT TO TIME.

WITH THE FENCES IN PLACE, WALTER AND HIS TEAM WAIT FOR THE AVALANCHE TO BE TRIGGERED.

[EXPLOSION] [EXPLOSION] [EXPLOSION] [EXPLOSION] [EXPLOSION] [EXPLOSION] TO THE NAKED EYE, THE RESULTING AVALANCHE IS INCREDIBLY FAST.

THE FENCES ARE DESTROYED WITHIN AN INSTANT OF EACH OTHER.

AND THE WHOLE THING IS OVER IN SECONDS.

LUCKILY, THE SLOW-MOTION CAMERAS HAVE CAPTURED EVERYTHING, ENABLING WALTER AND HIS TEAM TO ANALYZE THE ENTIRE EVENT, STARTING WITH THE MOMENT THE DYNAMITE IS DROPPED FROM THE HELICOPTER, CAUSING THIS EXPLOSION... AT THE TOP OF THE MOUNTAIN THAT RELEASES THE SLAB OF SNOW.

IMMEDIATELY, THE CENTRAL CORE IS SURROUNDED BY A POWDER CLOUD MADE UP OF 1% SNOW AND 99% AIR.

THIS IS A DRY POWDER AVALANCHE, THE FASTEST AND MOST DANGEROUS AVALANCHE OF THEM ALL.

THE AVALANCHE ACCELERATES DOWN THE STEEP INCLINE UNTIL IT REACHES THE FIRST FENCE.

THOUGH NOT EXACTLY AT THE ANGLE WALTER EXPECTED, THE LEADING EDGE HITS THE FIRST ONE... NOW.

AND THAT PARTICULAR PART OF THE SNOW FRONT REACHES THE SECOND FENCE... NOW...

MERE MOMENTS AFTER THE FIRST FENCE IS DESTROYED.

NO WONDER IT SEEMED SO QUICK.

IN FACT, THE DATA SHOWS THAT THIS AVALANCHE ONLY REACHED A VELOCITY OF 40 KILOMETERS AN HOUR, JUST 1/10 OF THE SPEED OF THE FASTEST ONE EVER MEASURED.

BUT 40 KILOMETERS AN HOUR IS STILL FASTER THAN THAT SLAB OF SNOW COULD HAVE ACHIEVED IF IT HAD JUST BEEN DROPPED FROM A GREAT HEIGHT.

SO HOW IS THAT POSSIBLE?

WELL, LIKE ALL WEATHER PHENOMENA, THERE IS MORE GOING ON INSIDE IT THAN MEETS THE EYE.

WALTER AND HIS TEAM TAKE TO THE SLOPES TO INVESTIGATE THE AFTERMATH OF THE AVALANCHE MORE THOROUGHLY.

AND HE EXPLAINS WHAT HAPPENS TO THE SNOW UNDERNEATH THE POWDER CLOUD AS THE AVALANCHE STARTS TO MOVE.

WALTER: FIRST, UM, THE SNOW COVER THAT RELEASES AND GETS ERODED, IT WILL BREAK INTO PIECES AND IT GETS ROUNDED A BIT, AND IT ALSO GETS COMPRESSED, SO IT CAN FORM SNOWBALLS.

NARRATOR: THESE SNOWBALLS MIGHT BE THE SECRET TO HOW AN AVALANCHE CAN MOVE SO FAST.

WALTER: THERE ARE STUDIES THAT SAY THAT REALLY IT'S THE RATIO BETWEEN THE BIGGER GRAINS-- OR THE BIGGER BALLS-- TO THE SMALLER BALLS THAT CAN SIG--SIGNIFICANTLY INFLUENCE THE SPEED AND THE MOTION OF THE AVALANCHE.

NARRATOR: 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, 4 TIMES FASTER THAN THE FASTEST FLASH FLOOD EVER MEASURED.

BUT, AS WE HAVE SEEN, WEATHER IS NOT ABOUT WATER ALONE.

ONE OF THE OTHER 3 KEY COMPONENTS CAN MOVE EVEN FASTER.

IT'S A POWERFUL FORCE THAT'S COMPLETELY INVISIBLE.

THAT FORCE IS WIND.

IN MANY WAYS, WIND IS THE MOST DRAMATIC OF ALL THE 3 MAIN INGREDIENTS BECAUSE IT DRIVES MOST OF THE PLANET'S EXTREME WEATHER: DUST DEVILS, WATER SPOUTS, TORNADOES.

ALL ARE SPINNING WINDS OF THE MOST INTENSE KIND.

EVEN HURRICANES AND CYCLONES ARE LARGE-SCALE WINDS WITH THAT SAME SPIRAL SHAPE.

TO SEE HOW THOSE SPIRALS COME ABOUT MEANS EXAMINING PERHAPS THE MOST UNUSUAL SPINNING WIND OF THEM ALL.

IT'S CALLED A FIRE WHIRL, AND BECAUSE IT'S MADE ENTIRELY OF FLAMES, IT SHOULD BE EASIER TO WATCH THE TWISTING STRUCTURE AT WORK.

AUSTRALIA HAS MORE KNOWN FIRE WHIRLS THAN ANYWHERE ON THE PLANET, BUT IT'S VERY RARE TO ACTUALLY SEE ONE.

WHICH IS WHY THE BEST WAY TO EXAMINE A FIRE WHIRL... IS TO BUILD ONE.

DR. KAZUNORI KUWANA AND ENGINEER KOZO SEKIMOTO ARE GOING TO DO EXACTLY THAT.

THEY HAVE SPENT THE LAST 10 YEARS LOOKING AT HOW AND WHY FIRE WHIRLS SPIN.

BUT THEY'VE NEVER MANAGED TO CAPTURE THE MOMENT WHEN THAT CYCLICAL MOTION IS TRIGGERED.

THEY'RE HOPING TODAY WILL CHANGE ALL THAT.

WHAT THEY DO KNOW IS THAT THE FIRE NEEDS TO BE AN ASYMMETRIC SHAPE, WHICH IS WHY THEY'RE LAYING THESE BAKING PANS OUT IN THE PATTERN OF A GIANT LETTER "L." NEXT, THEY TAKE A HIGHLY FLAMMABLE LIQUID CALLED HEPTANE AND FILL THE PANS WITH IT.

HEPTANE BURNS FIERCELY AND SHOULD CREATE ENOUGH HEAT FOR A FIRE WHIRL TO START SUCKING IN OXYGEN, AND THAT IS CRUCIAL.

THE PRINCIPLE CAN BE DEMONSTRATED BY LIGHTING A COOKER.

[DIAL CLICKING] HOT AIR RISES FROM THE FLAMES, MAKING THE AIR ABOVE THEM LESS DENSE.

AND BECAUSE IT'S LESS DENSE, IT MAKES THE AIR PRESSURE THERE LOWER.

BUT THE COLD AIR AROUND THE COOKER IS STILL AT NORMAL PRESSURE, SO IT RUSHES IN TO FILL THE GAP, TURNING THESE CHILDREN'S WINDMILLS.

USING THE SMOKE FROM THIS MATCH, WE CAN SEE THAT MOVEMENT OF AIR.

THE FLAMES ARE SUCKING THE OXYGEN IN.

THE COLDER, HIGH-PRESSURE AIR IS RUSHING IN TO FILL THE GAP LEFT BY THE WARMER, LOW-PRESSURE AIR.

AND IT'S THE AIR RUSHING IN OPPOSING DIRECTIONS THAT TRIGGER THE FIRE WHIRL.

THAT'S WHAT KAZU AND KOZO'S "L" SHAPE IS ALL ABOUT.

BUT IS IT ACTUALLY GOING TO WORK?

AT FIRST, THE EXPERIMENT DOESN'T LOOK TOO PROMISING.

BUT AS COLD AIR RUSHES IN, IT FEEDS THE FLAMES.

AND THEN, QUITE SUDDENLY, THEY START TO SPIN.

THE SPIN SEEMS TO INTENSIFY THE FIRE EVEN MORE.

THE FLAMES CONTINUE TO GROW UNTIL THEY ARE MORE THAN 10 METERS TALL... A REAL-LIFE FIRE WHIRL.

BY INTRODUCING SMOKE, KAZU AND KOZO HOPE TO MAKE THAT SPINNING WIND VISIBLE.

THE CROSSWIND IS SO STRONG, BUT ON THE FAR SIDE, IT BLOWS IN A PRETTY STRAIGHT LINE.

BUT ON THIS SIDE, THE SMOKE IS BEING PULLED IN TWO DIRECTIONS AT ONCE, TOWARDS BOTH ARMS OF THE "L." THAT CREATES THOSE LITTLE GREEN SWIRLS AND ULTIMATELY THE FIRE WHIRL ITSELF.

NATURAL "L" SHAPES OCCUR WHEN TWO SEPARATE FIRE FRONTS MEET, EACH CREATING THEIR OWN OPPOSING WINDS.

[THUNDER] AND OTHER TYPES OF SPINNING WEATHER START IN MUCH THE SAME WAY.

TWO OR MORE WINDS MEETING AT DIFFERENT ANGLES AND SPEEDS, SOME RISING WARM AIR AND COLD AIR RUSHING IN TO FILL THE GAP.

THAT FORMULA IS SO POTENT THAT IT'S CAPABLE OF CREATING THE MOST POWERFUL AND DEADLY WIND OF THEM ALL...

THE TORNADO.

TORNADOES AREN'T THE FASTEST WIND ACROSS THE GROUND.

THEIR TOP SPEED IS ONLY 110 KILOMETERS AN HOUR.

BUT THE SPEED THAT THEY CAN SPIN IS FORMIDABLE.

IT IS THIS SPIN THAT GIVES TORNADOES THEIR DEVASTATING POWER.

SO IT'S SURPRISING TO LEARN THAT DESPITE DECADES OF INTENSE STUDY, NOBODY KNOWS EXACTLY HOW FAST THEY CAN SPIN.

HERE IN BOULDER, COLORADO, THE CENTER FOR SEVERE WEATHER RESEARCH HAS LONG BEEN AT THE FOREFRONT OF TORNADO RESEARCH.

ITS PRESIDENT, JOSH WURMAN, EXPLAINS WHY SPIN SPEEDS ARE STILL SUCH A MYSTERY.

JOSH: SCIENTISTS HAVE GOTTEN VERY GOOD AT MEASURING THE WINDS ABOVE THE GROUND IN THE TORNADO, MAYBE FROM 50 METERS ABOVE THE GROUND UP TO A COUPLE KILOMETERS.

BUT THE STRONGEST WINDS IN THE TORNADO ARE BELOW THAT.

THE STRONGEST WINDS MIGHT EVEN BE BELOW 10 METERS.

USING REMOTE SENSING WITH RADARS, WE CAN GET UP CLOSE, WE CAN SCAN BACK AND FORTH, BUT, UNFORTUNATELY, OBJECTS BLOCK US.

THERE'S DEBRIS, PIECES OF HOUSES, COWS, WHATEVER, FLYING AROUND IN THE TORNADO, AND THAT'S THE ONE PLACE WHERE WE ARE THE MOST BLIND.

NARRATOR: THE ALTERNATIVE APPROACH HAS BEEN TO TRY TO GET MEASURING INSTRUMENTS INSIDE A TORNADO, BUT THAT HAS PROVED EQUALLY DIFFICULT.

JOSH: THERE ARE TWO MAIN CHALLENGES WITH IN SITU MEASUREMENTS.

THE FIRST IS HOW TO GET SOMETHING INSIDE THE TORNADO.

THE TORNADO IS MOVING DOWN THE FIELDS, AND WE DON'T KNOW EXACTLY HOW IT'S GOING.

IT'S AN UNPREDICTABLE PATH.

SO GETTING SOMETHING IN FRONT IS VERY, VERY HARD.

CHALLENGE NUMBER TWO IS WHAT HAPPENS WHEN WE SUCCEED, AND THAT IS, THE TORNADO RUNS OVER THE OBJECT AND DESTROYS IT.

SO UNFORTUNATELY, THE PLACE THAT WE MOST NEED TO KNOW ABOUT IS THE PLACE THAT'S HARDEST FOR US TO SEE.

WE NEED TO UNDERSTAND WHAT'S HAPPENING IN THOSE STRONGEST LEVELS OF THE TORNADO WHICH ARE CAUSING THE DAMAGE.

IF WE CAN UNDERSTAND THAT BETTER, THEN ENGINEERS WILL BE ABLE TO BUILD BETTER BUILDINGS, WE'LL BE ABLE TO HAVE BETTER SHELTERS, AND FEWER PEOPLE WILL GET INJURED AND DIE IN TORNADOES.

NARRATOR: BUT WORK IS BEING DONE TO TRY AND MEASURE THE SPEED OF TORNADOES NEAR THE GROUND.

THIS IS THE WIND ENGINEERING, ENERGY AND ENVIRONMENT RESEARCH INSTITUTE, OR WINDEEE, FOR SHORT.

AND IT'S THE ONLY PLACE ON THE PLANET CAPABLE OF DUPLICATING THE REAL-LIFE DYNAMICS OF A TORNADO.

THE WHOLE STRUCTURE COST $23 MILLION.

ITS DIRECTOR, PROFESSOR HORIA HANGAN, EXPLAINS HOW IT WORKS.

HORIA: WE HAVE A BUNCH OF FANS ON THE PERIPHERY HERE, SO THERE ARE 6 WALLS, AND ON EVERY ONE OF THOSE WALLS, THEY--THERE ARE 8 FANS.

SO YOU BLOW AIR THROUGH THE FANS AT THE BASE, UH, AND YOU SET LOUVERS AT DIFFERENT ANGLES IN FRONT OF THE FANS, SO THAT GIVES THEM A TWIST.

THE AIR COMES IN THE CHAMBER WITH A TWIST.

AND THEN YOU HAVE THIS BELL MOUTH AT THE TOP AND ANOTHER COUPLE OF FANS, 6 LARGER FANS, WHICH ARE ABOVE THE CEILING LEVEL, AND YOU RUN THOSE IN REVERSE SO THEY CREATE A SUCTION.

SO TWIST PLUS SUCTION-- THAT'S A MANMADE TORNADO.

NARRATOR: PROFESSOR HANGAN IS GOING TO ATTEMPT TO MEASURE THE SPEED OF THAT MANMADE TORNADO RIGHT NEXT TO THE GROUND, USING TRACKING TECHNOLOGY AND A BIG BOX OF PINK FOAM SQUARES.

THESE SQUARES SHOULD BE LARGE ENOUGH FOR THE TRACKERS TO FOLLOW BUT STILL LIGHT ENOUGH FOR THE TORNADO TO DRAW THEM UP.

WE'RE GONNA START THE FANS.

NARRATOR: BUT AS YET, THIS TECHNOLOGY IS ENTIRELY UNTESTED.

WE'LL GO A LITTLE BIT UP WITH THE UPDRAFT OF 35%.

[BEEP] HORIA: WE'LL JUST GO UP TO 40.

NARRATOR: THAT'S IT.

THEY'RE UP.

THE PINK FOAM SQUARES ARE FLYING SUCCESSFULLY.

BUT CAN HORIA AND HIS TEAM MEASURE HOW FAST THEY ARE FLYING?

THEY TURN ON THE TRACKING TECHNOLOGY.

THE COMPUTER FOLLOWS INDIVIDUAL SQUARES ONE AFTER ANOTHER SO IT CAN CREATE AN AVERAGE SPEED FROM ALL THE DIFFERENT FLIGHT PATHS.

AND IT WORKS.

ACCORDING TO THE CALCULATIONS, THE TORNADO IS SPINNING AT A SHADE OVER 35 KILOMETERS AN HOUR, THE FIRST TIME ONE HAS EVER BEEN MEASURED THIS NEAR THE GROUND.

SO THE CONCEPT OF TRACKING IS A GOOD ONE, BUT A REAL TORNADO IS ABOUT A HUNDRED TIMES BIGGER AND MUCH, MUCH FASTER, MEANING IT'S STILL A PROBLEM GETTING NEAR ENOUGH TO PUT SOMETHING INSIDE ONE.

HOWEVER, A TEAM OF METEOROLOGISTS FROM OKLAHOMA THINK THEY MAY HAVE FOUND THE ANSWER... WITH THIS.

THIS BIZARRE VEHICLE IS THE DOMINATOR 3, A HAND-BUILT TORNADO-PROOF ARMORED CAR.

AND IT'S EQUIPPED WITH A ROOF CANNON THAT CAN FIRE TRACKING DEVICES STRAIGHT INTO A TORNADO.

ONCE THE PROBE IS AT PEAK HEIGHT, A PARACHUTE POPS UP, ALLOWING IT TO BE SUCKED INTO THE TORNADO.

SO, USING THE DOMINATOR, CAN THE OKLAHOMA TEAM ACTUALLY MANAGE TO MEASURE THE SPEED OF A TORNADO AT ITS BASE?

THEY INTEND TO FIND OUT.

IT TAKES THEM 6 WEEKS INTO TORNADO SEASON, BUT FINALLY METEOROLOGIST REED TIMMER AND HIS CREW ARE HOT ON THE HEELS OF A REAL-LIFE TWISTER.

THE TRICK NOW IS TO GET AS CLOSE AS THEY DARE, CLOSE ENOUGH TO FIRE A PROBE STRAIGHT INTO ITS HEART.

OH!

NARRATOR: BUT THAT IS NO SIMPLE TASK.

TORNADO WARNING... NARRATOR: THE PATH OF A TORNADO IS NOTORIOUSLY UNPREDICTABLE.

TWO MILES TO OUR SOUTHEAST.

GETTING REAL CLOSE.

NARRATOR: REED AND HIS TEAM ARE DETERMINED.

IT'S RIGHT HERE.

OH, WE HAVE VISUAL HERE.

NARRATOR: IF THEY CAN CRACK THE PROBLEM OF MEASURING TORNADO SPEED IN THE WILD, THEN IT COULD REVOLUTIONIZE THE WAY WE DEAL WITH THESE MASSIVE WINDS.

BUT AS THEY GET CLOSER, THE DANGERS INVOLVED BECOME ALL TOO EVIDENT.

THEY PRIME THE DOMINATOR FOR ACTION.

THERE IT IS.

ON THE GROUND.

SEE?

TORNADO ON THE GROUND.

RIGHT THERE.

STRAIGHT AHEAD.

CUT IT, CUT IT, CUT IT!

STRAIGHT AHEAD.

GO!

OH, THAT'S HUGE!

NARRATOR: IT IS HUGE-- ABOUT A HUNDRED METERS ACROSS AND AT LEAST A KILOMETER TALL.

THEY GET THE DOMINATOR AS CLOSE AS THE ROAD WILL TAKE THEM.

REED: STOP, STOP, STOP, STOP!

PERFECT!

THIS IS IT.

LET'S STOP.

LET'S STOP.

OH, MY GOD.

NARRATOR: THE TORNADO IS COMING STRAIGHT FOR THEM.

IT'S COMING RIGHT AT US!

GET READY TO SHOOT!

COMING AT US.

RIGHT HERE!

GET THIS OFF!

NARRATOR: IT'S PERFECT.

DEPLOY!

DEPLOY!

DEPLOY, KEVIN!

DEPLOY!

DROP IT DOWN!

GET IN.

NARRATOR: UNFORTUNATELY, AS THEY TRY TO MAKE THE VEHICLE SECURE, REED'S WINDOW FAILS.

PULL YOUR WINDOW UP.

TELL ME WHEN.

NARRATOR: HE HAS TO RESORT TO PULLING IT UP BY HAND.

WE'RE IN IT.

WE'RE IN IT.

WE'RE IN IT.

SHOOT!

SHOOT!

DEPLOY!

SHOT IT!

IT'S IN!

IT'S RIGHT THERE NEXT TO US!

I'VE SEEN IT GO ALL THE WAY AROUND.

IT WENT ONE FULL REVOLUTION.

NARRATOR: IT'S IN.

YOU NEED WIDER EYES, THAT'S ALL.

HA HA HA!

NARRATOR: THEY GOT THE PROBE INSIDE.

I NEEDED THAT.

YEAH!

CREW MAN: I SAW IT MAKE ONE FULL REVOLUTION.

THEN I LOST VISUAL ON IT, SO I KNOW IT AT LEAST WENT AROUND ONE TIME.

NARRATOR: BUT THAT'S ONLY HALF THE CHALLENGE.

NOW THEY NEED TO RETRIEVE THE PROBE TO FIND OUT WHAT IT RECORDED.

HOPE WE GOT SOME GOOD STUFF ON THERE, MAN.

NARRATOR: THEY WAIT FOR THE STORM TO PASS, THEN SET OFF OUT THROUGH THE TRAIL OF DEVASTATION IN SEARCH OF THE PROBE.

SO, HOW FAR AHEAD DO YOU THINK IT IS?

PROBABLY ABOUT 3 MILES, I WOULD SAY.

NARRATOR: FOR SOME REASON, THEY'RE NOT PICKING UP ITS GPS SIGNAL, SO THEY'RE REDUCED TO SEARCHING ON FOOT.

WHEN I LAUNCHED IT, I SAW IT GO OUT OVER THE ROAD THAT WAY.

IT SPUN AROUND LIKE THIS, ALL THE WAY AROUND, AND IT DESCENDED EITHER BEHIND THESE TREES OR THESE TREES RIGHT HERE, SO WE'RE WITHIN A COUPLE OF HUNDRED FEET OF IT RIGHT NOW.

OK.

SO IT'S GOT TO BE SOMEWHERE OVER THIS WAY OVER HERE.

NARRATOR: AGAINST ALL THE ODDS, THEY SPOT IT.

WHOO-HOO-HOO!

YEAH, BABY!

WHOO-HOO!

YEAH!

NARRATOR: REED AND HIS TEAM HAVE ACCOMPLISHED SOMETHING THAT NO ONE HAS EVER DONE BEFORE... HIGH FIVE!

NARRATOR: THEY'VE MANAGED TO GET A FLYING PROBE INTO THE BASE OF A TORNADO.

WE DID IT!

HA HA HA!

WHOO!

TODAY IS THE FIRST TIME WE'VE RECOVERED ONE THAT WE KNOW WAS INSIDE A TORNADO, SO THIS IS A HUGE SUCCESS FOR OUR SCIENCE MISSION, AND I'D SAY THIS IS DEFINITELY A STEPPINGSTONE FOR THINGS TO COME IN THE FUTURE.

NARRATOR: IT'S A PROUD MOMENT... [INDISTINCT CHATTER] BUT THIS IS REAL LIFE.

THE PROBE WAS DAMAGED IN ITS TRIP AROUND THE TWISTER.

AS YET, THEY HAVEN'T MANAGED TO RETRIEVE ANY OF ITS DATA.

SO THEY'RE PLANNING ON DOING IT ALL OVER AGAIN.

MOST OF US WILL NEVER HAVE TO LIVE THROUGH A TORNADO.

BUT THERE IS ONE TYPE OF EXTREME WEATHER WE'VE ALL EXPERIENCED, AND IT'S A FITTING CONCLUSION, BECAUSE IT REQUIRES ALL 3 OF THE KEY INGREDIENTS THAT WE'VE LOOKED AT IN THIS PROGRAM: TEMPERATURE... WATER... AND WIND.

WHEN HEAT MAKES THE GROUND INTENSELY WARM AND THE AIR IS HEAVY WITH WATER VAPOR, AND STRONG WINDS MOLD THE CLOUDS, YOU CREATE... [THUNDER] A THUNDERSTORM.

MOST OF US ARE FAMILIAR WITH THUNDER AND LIGHTNING.

WE KNOW LIGHTNING IS A POWERFUL BOLT OF ELECTRICITY, AND THUNDER IS THE NOISE THAT ACCOMPANIES IT.

[THUNDER] BUT IN ITS OWN WAY, THUNDER IS EVERY BIT AS DESTRUCTIVE AS LIGHTNING.

THIS IS ONE OF THE FEW PLACES IN THE WORLD CAPABLE OF CREATING FULL-BLOWN THUNDER.

THEY DO IT BY FIRING 200,000 AMPS OF ELECTRICAL CURRENT DOWN THIS NARROW COPPER WIRE-- EXACTLY THE SAME AMOUNT OF CURRENT THAT'S IN A REAL LIGHTNING BOLT.

CHIEF SCIENTIST DAN MORGAN EXPLAINS HOW THEY GO ABOUT IT.

DAN: WELL, THIS IS CONTROLLING OUR LIGHTNING GENERATOR, SO IT CAN PRODUCE A SIMULATED, UH, BOLT OF LIGHTNING AND THE CORRESPONDING THUNDER.

SO FIRST OF ALL WE RAISE THE EARTHS, WHICH, UH, EARTH, THE WHOLE SYSTEM.

SO WE CAN NOW RAISE THE DUMPS, AND NOW WE'RE IN A POSITION TO CHARGE.

WE'RE NEARLY THERE.

WE'RE STORING ENERGY IN THE CLUSTERS FOR A DURATION OF A MINUTE OR SO AND THEN RELEASING ALL THAT ENERGY VERY QUICKLY.

[THUD] NARRATOR: THAT SHORT, SHARP "BANG"... [BANG] WAS ACTUAL THUNDER, EVEN THOUGH IT'S NOT THE SOUND WE'RE USED TO HEARING.

BECAUSE A BOLT OF LIGHTNING IS AROUND A KILOMETER LONG, SOME OF THAT SOUND GETS TO US QUICKER THAN OTHER BITS, SO WHAT WE NORMALLY HEAR IS MULTIPLE ECHOES OF THAT INITIAL SHORT "BANG."

BUT THUNDER IS NOT JUST ABOUT SOUND, AS DAN IS ABOUT TO DEMONSTRATE, USING SLOW-MOTION CAMERAS AND A LINE OF LIT CANDLES.

[BEEPING] [EXPLOSION] IN THE AFTERMATH OF THE DISCHARGE, THE CANDLES ARE ALL BLOWN OUT.

[EXPLOSION] AND IF YOU WATCH CAREFULLY... YOU CAN SEE THAT THEY ARE BLOWN OUT ONE BY ONE.

SO WHAT IS GOING ON?

WELL, IT'S ALL TO DO WITH TEMPERATURE.

DAN: WE GET OUR LIGHTNING ARC, AND WE HAVE A HUGE, UH, TEMPERATURE INCREASE.

THAT HEATS THE AIR UP SURROUNDING THE ARC, AND THAT MOVES FASTER THAN THE SPEED OF SOUND, WHICH CAUSES A SHOCK WAVE, WHICH, UH, WE HEAR AS THUNDER.

AND, UH, THAT'S WHAT WE'VE JUST PRODUCED THERE.

[THUNDER] NARRATOR: BECAUSE LIGHTNING IS SO FEROCIOUSLY HOT, IT EXPLODES THE AIR AROUND IT... [THUNDER] CAUSING IT TO RUSH OUTWARDS.

WHAT WE SEE WITH THE CANDLES IS THAT AIR MOVING AWAY FROM THE LIGHTNING BOLT IN A SHOCK WAVE.

THE SCIENTISTS HERE AT COBHAM ARE INTERESTED IN THE EFFECTS OF THIS SHOCK WAVE.

THEY'RE TRYING TO MEASURE JUST HOW POWERFUL IT CAN BE.

FOR INSTANCE, IS IT STRONG ENOUGH TO SHATTER GLASS?

DAN: WE CERTAINLY THINK THAT THE INNER RING OF LIGHT BULBS WILL GO.

WE'RE NOT QUITE SO SURE ABOUT THE OUTER RING.

ONE WAY TO FIND OUT.

[EXPLOSION] NARRATOR: THE BULBS HAVE BEEN DESTROYED BY THE SHEER FORCE OF THE HOT AIR EXPLODING OUTWARDS-- IN OTHER WORDS, THE THUNDER.

[EXPLOSION] [GLASS BREAKING] NOTICE IT'S NOT THE LIGHTNING DESTROYING THE LIGHT BULBS.

THE ARC NEVER EVEN TOUCHES THEM.

[GLASS BREAKING] IT'S THE SHOCK WAVE AFTER THE FLASH THAT DOES THE DAMAGE.

NOTICE ALSO THAT THE SOUND OF THUNDER HAPPENS EVEN LATER, AFTER THE FLASH... [BANG] AND AFTER THE BULBS HAVE EXPLODED.

BY USING AN EVEN MORE SPECIALIZED CAMERA, THE TEAM CAN ACTUALLY ATTEMPT TO CAPTURE THAT SHOCK WAVE ONSCREEN-- NOT THE EFFECTS BUT THE ACTUAL SHOCK WAVE ITSELF.

THAT IS THE AIR EXPLODING AWAY FROM THE HOT LIGHTNING BOLT AT OVER 1,100 KILOMETERS AN HOUR.

SO THERE'S THE SECRET.

YOU CAN ACTUALLY SEE THUNDER.

[EXPLOSION] [THUNDER] WEATHER IS ENDLESSLY FASCINATING... A STUNNING DISPLAY OF MAGIC AND SPECTACLE, PERFORMED IN FRONT OF US EVERY SINGLE DAY.

[THUNDER] EVEN WHEN CONDITIONS ARE WET AND MISERABLE, THERE ARE AMAZING EVENTS GOING ON JUST BEHIND THE SCENES.

AND THOUGH IT MAY SEEM THAT ONLY EXTREME WEATHER IS WORTHY OF OUR ATTENTION...

THE WEATHER AROUND US EVERY DAY IS EQUALLY... [EXPLOSION] FULL OF WONDER.

WILD WEATHER IN ALL ITS GLORY.

ANNOUNCER:"WILD WEATHER" IS AVAILABLE ON DVD.

TO ORDER, VISIT SHOPPBS.ORG, OR CALL 1-800-PLAY-PBS.