THE sirens screeched their ear-splitting warning as a swirling tableau of blacks and greys turned the skies from day to night over rural Arkansas.
In the muggy late afternoon, a lethal belt of tornado-sparking thunderstorms was powering its destructive path towards the small towns in the rolling hills of the Ozarks.
Last week’s sirens screamed a life-or-death instruction - take refuge immediately in the nearest basement or shelter - as the first major tornado outbreak of the year raked through America’s heartlands.
Yet even as streets emptied and rain lashed down, an armour-plated vehicle that looked as though it had just emerged from a Mad Max movie rolled into town.
Behind the wheel, Sean Casey popped another wad of chewing tobacco into his mouth and scanned the storm's progress through the bullet-proof windscreen. Next to him, his navigator and meteorologist Skip Talbot pored over the yellow, green, orange and red swirls of radar on a computer lap-top screen.
A tornado had just touched down five miles to the west, flattening a church, demolishing or damaging dozens of clapperboard homes and flipping an articulated lorry. Hence why we were there.
As others flee tornados, Mr Casey and his team heads towards them. The star of the television series Storm Chasers, a hit in Britain and America, he was the first man to drive voluntarily into a tornado to capture the power and the drama at its heart on film.
The Sunday Telegraph last week joined Mr Casey and his team in his "Tornado Intercept Vehicle" (known to all as the TIV) for an adrenalin-pumped 1,800-mile, three-day and four-state chase in their hunt for one of the most dramatic but unpredictable of weather phenomena.
The television show and current IMAX documentary Tornado Alley may have made Mr Casey a celebrity in America's storm-prone states. But it is the instantly-recognisable TIV that stops admirers along the route.
The customised vehicle, invented and welded together by Mr Casey in his garage, is a seven-ton pick-up truck encased in a protective shell of 2-inch thick metal and 1.5-inch glass. It can reach speeds of 100mph and barely scrapes 11 miles to a gallon of diesel, though it has such a large tank that it can still range 750 miles between refills.
A glass turret built into the roof allows Mr Casey to film from a 360-degree rotating chair, similar to a gunner's seat in a military vehicle. Its distinctive tail contains the weather data instruments.
The unique silhouette of the Tornado Intercept Vehicle, top, as a storm system approaches Photo: JENNIFER BRINDLEY
As the storm gathered pace towards us, we took to a hilltop vantage point and the TIV prepared to "deploy" to withstand a tornado. If one approached, instead of turning tail Mr Casey would use the hydraulics to drop the vehicle into a defensive position close to the ground, lower its metal skirting side-panels to the surface and sinking four spikes into the earth. "No vehicle is completely tornado-proof but we would be in pretty good shape if we deployed," he said.
To the west, out of sight in the nearby hills, a super-cell thunderstorm was spawning a violent rotating funnel of air that was in contact with both the cloud and ground – the definition of a tornado.
Lightning strikes crackled down into the valley floor from the churning blanket of clouds as he thunder growled closer. Then a deafening clap exploded right above the TIV as a spectacular burst of lightning lit the darkening sky with a blinding flash of white.
"Don't touch the frame, don't touch anything metal," Mr Talbot instructed as we huddled inside.
Mr Casey chewed and contemplated. "Nothing to do but sit tight," he said. "Guess that was 100 feet away."
The storm passed over us without forming a new tornado. But elsewhere the same system produced the first twisters of the year across several states, killing at least three people, as a new season of "severe weather" kicked in.
As he studied the latest radar Mr Casey recalled his most terrifying encounter with nature when a tornado turned hunter, the TIV its prey.
"We had been chasing a storm for two hours one evening near Stuttgart in Arkansas, but no tornado developed, when we got a report of a tornado forming in the town itself. We drove into town but it was almost pitch black and you could barely see a thing.
"Then suddenly a tornado was right there, behind us, getting bigger and bigger. It was wider than it was tall, those are the really dangerous ones, and had winds of 240mph inside.
"We deployed the panels and sank the spikes and sat it out, but we took a real battering and there were telephone poles flying down on us.
"I could feel a really dark pressure at the back of my neck and spine. It was the sensation of death perched on my shoulder. That was a truly hair-raising experience."
The prairies that stretch south from the Canadian border, through the Great Plains to the hills and river deltas of the Deep South, are a world where nature is at its most capricious.
This swath of land between the Rockies and Appalachian Mountains is colloquially known as "tornedo alley" for good reason – nearly all the world's twisters occur here.
The funnels are often encircled by much larger shrouds of debris and dust. Most have inner wind speeds of less than 110mph, are about 250 ft across and move across the ground at up 30mph, travelling only a few miles, perhaps just hundreds of yards, before dissipating. But the bigger twisters can twist internally at more than 300mph and stretch more than two miles across.
They remain one of the greatest mysteries of meteorology, extremely difficult to predict even as other weather forecasting techniques have become more accurate.
Mr Casey's storm-chasing strategy is to identify the course of a tornado – no easy task – from radar and the contours of the land and then position the TIV in its path. The hope is effectively to tether the vehicle to the ground to withstand the pounding rain and howling winds that can swirl up to 300mph inside a twister.
But at other times, as he has raced down country roads to play catch-up or as tornados have veered away, he has driven unexpectedly into the heart of one. In a scene in Tornado Alley, the storm engulfs the TIV in a breathtaking moment Pursuing the twists and turns of the weather front last week, we had witnessed the worst as our odyssey took us through Joplin, the south-western Missouri city that was partly-obliterated two years ago when the strongest tornado in recent history descended on it - killing 158 people along its path before it finally petered out.
Mr Casey, a film-maker who picked up the storm-chasing bug 14 years ago when chronicling the obsession of another, is now shooting Wild Weather 3D, an IMAX documentary about tornados, hurricanes and monsoon lightning. He frequently travels with his wife Jennifer, a theatre studies graduate who specialised in Shakespeare but who is now just as much at home in Wichita as in Stratford.
Many other storm chasers, however, leave their spouses at home and organise their work around their obsession - like Mr Talbot, a computer software programmer who works from home in central Illinois.
"I was a storm chaser before I met my wife and she understood I would be away for large parts of the season," he said.
"I've had a lifelong fascination with storms and tornadoes, and started actively chasing them in 2003 while I was in college. It's since turned into a drug-like addiction that I devote huge amounts of time toward.
"When I was seven years old, the neighbouring town of Plainfield was destroyed by a tornado. I was living mere miles from the track at the time, and the tornado was mythical to me, striking without warning and with atomic bomb-like damage." Mr Talbot and his fellow devotees spend the chase season dissecting models and projections, eagerly awaiting over-night predictions and excitedly discussing "multiple vortexes" and "bubbling convection" on social media sites such as the Spotter Network.
Last week, The Sunday Telegraph joined their posse for a series of back-breaking dawn-to-dusk drives that started with a "30 per cent" probability of tornadoes -- as good as it gets in the storm-chasing world where most days start with great hope and expectation but end in disappointment and frustration.
The weather maps took us racing first west across Kansas to eastern Colorado, where corkscrewing thunderstorm clouds filled the skies and hail-stones the size of ping-pong balls rattled the TIV with a deafening onslaught.
But an unexpectedly violent cold front descending through from the Arctic disrupted what had been a tornado-rich projection. The less dedicated would head home. The storm chasers instead drove east for 1,000 miles to pursue their dreams.
"It's the surge of expectations that kill you," said Mr Casey. "The thrill is the roller-coaster. Never know what we're going to encounter, there is always that heightened sense of possibility. But nothing can match the excitement of capturing a tornado. The thrill is impossible to describe in words.
"It's like going to Vegas. You never know what's going to happen. Are you going to hit the jackpot or are you going to lose it all? Chasers are gamblers.
"There are long tiring drives when you wonder why you are doing this. But then it really pays off when you see something incredible and it feels like you are in the middle of weather from another planet."
Indeed, the Great Plains seem endless and monotonous to most, but for chasers this terrain makes them giddy with excitement. The landscape stretches to the horizon, no hills or furrows to confuse the eye, the cloud cover low and enticing as they converge on their target areas. The hills of Arkansas provide much greater challenges to them, as we discovered last week.
The chase is part high-tech, deploying the latest in weather radar applications, part word of mouth, relying on tips and reports over ham radio. A tornado warning elicits yells and shouts of anticipation as wheels squeal and the posse roars off in search of the latest sighting. The cracked windscreens and dented bonnets of their vehicles are badges of honour, battles scars from the hailstones of previous storms.
For Americans for whom tornados are a way of life, the chasers' devotion is as mystifying as it is impressive. "My kids and I had three minutes to get to a basement when the sirens started," said Yvonne Whiteside, whose home just outside Wichita was destroyed by a tornado in 1999.
"I am delighted that they are out their researching as the more we know, the better. But rather them than me. I've experienced a tornado up close. I never want to experience another."
By Philip Sherwell, Telegraph.co.uk