Lightning flashed all around us as we drove along the I-80 freeway for the umpteenth time that week, but this time things were different. We'd just seen a stunning tornado racing across the plains in beautiful afternoon light – but the supercell storm that produced it was now chasing us down for revenge.
As heavy hail began to batter our chase vehicle, our minute-by-minute satellite data told us exactly what we didn't want to hear. "Tornado on the ground, North Paxton," said our navigator, Gabriele. "That was reported four minutes ago, and now it will be exactly where we are, so look out the window and tell me if you see anything."
So I stared out the left side window through the flashing sky hoping, this time, I would not see a tornado. Visions of rolling cars and flying debris raced through my head as the dangers everyone had warned me about became very, very real. Our Hummer H3 was tough, but was it tough enough to beat a tornado?
The question I was asked most before setting off for Tornado Alley, in the Midwest of the United States, was: "Have you seen the movie Twister?" My answer had been simple: "No, I haven't, and I'm not going to watch it until I get home. And anyway, I've been promised this is going to be nothing like the movie."
Violent tornadoes do lay swathes of destruction across the central United States every year, tearing houses apart, throwing cars around and demolishing everything in their path – but to many, they are predictable forces of nature that have a fascinating mix of danger and beauty, which is why hundreds of people come to chase every year.
This season, which began early in April and will end next month, saw the start of Vortex2, the biggest-ever scientific research to discover how nature forms these devastating funnels of air. I joined the scientists, television crews and fanatical amateur storm-chasers on the roads to see what we could find.
The popularity of Discovery's Storm Chasers television programme has also led to a boom in tourism; now storm tourists, who pay upwards of £2,000 for a 10-day trip, can join the chase to seek and survive a tornado. I suppose it's the same instinct that drives others to follow predators in Africa, hoping for the "kill" to make the trip.
"The tour groups want to get people in really close," expert storm chaser and former tour guide Tim Marshall explained to me. "There's no science involved, it's just an 'ooh, aah' tour for people to get their picture in front of the tornado. It's a popular thing to do and it seems to be increasing."
But it is not easy to snare your first tornado. Even in Tornado Alley, which stretches from the Texas panhandle in the southern United States through Colorado, Oklahoma and Kansas to the northern regions of Wyoming, Nebraska and Iowa, there is only a narrow window of good weather for the storm chaser, and only a handful of days when the stormy skies produce the ultimate prize.
Statistically, the greatest chance of tornadoes occurring here is in late May, but they happen any time during late spring and early summer, when the subtropical jet stream, which usually hugs the Gulf Coast, shifts north over the plains states, bringing with it the weather disturbances that generate thunderstorm outbreaks.
When the jet stream steers warm, moist air north from the Gulf of Mexico into cooler, drier air flowing east from the Rockies, these air masses collide. If they hit at an appropriate angle they create a spinning storm, called a supercell, which, given high moisture levels and enough rotation, can strengthen into a tornado.
When I arrived, a weather "peak" over the US had dampened all instability for three weeks, leaving tour groups and scientists alike driving disappointedly around the plains.
Luckily, storm chasing is as much about experiencing the unique Midwest culture as it is about homing in on a brewing storm. The endless flat corn plains of Kansas, the crumbling sand hills of Nebraska and the rolling fields of Minnesota are places you might otherwise avoid, but each has its charms.
In Colby, Kansas – a small city known as "the Oasis on the Plains" – I ventured into a bar called Twister's and met Eldon, a rotund corn farmer who wore a food-stained shirt. "I saw eight tornadoes in one day in '97," he said. "I watched one pull up a tree then drop it, roots and all, back in the same hole. We don't worry about them, really, but I guess they can be dangerous when you drop your guard."
Grand Island, where a tornado ripped through downtown in 1980, has a poignant memorial to the destructive power of the twister: a hill in the town's central park is constructed from the rubble.
"It was a total mess," said one of the residents I met. "There were concrete blocks from a hotel speared through trucks and houses."
Drop into Wakita and you will find the same thing reproduced by Hollywood. The town's tiny Twister Museum is dedicated to the year when movie producers destroyed all the derelict buildings, leaving empty lots that remain to this day – alongside "twister park", which was constructed from the rubble of the make-believe tornado.
Elsewhere, signs exhort the visitor to "see the 80-foot Vincent van Gough" in Goodland or "visit the second-friendliest yarn store" in Salina, not to mention "Kansas's only five-legged live cow". So, while the chase takes time, there's plenty of entertainment on offer.
It's no easy business spotting a storm; the ones here develop so quickly you have to be on them before you even see signs in the clouds. To do this, spotters – be they scientists, enthusiasts or tour guides – use the very latest in technology, chasing footprints in the skies using constantly updated satellite data.
It wasn't long ago that storm chasing was done by eye and a payphone to get the latest weather information. Now, in-car laptops are fed with data from a highly precise network of radars providing colourful plots of where the precipitation and winds are building.
"You want a [travel] company that has meteorologists with a lot of chasing experience," Marshall explained. "That's something you must think of before you book a tour, because there are lots who claim to be something they are not. Check around, talk to people who have been on tours, see how they like them, or you might be disappointed."
Fortunately, I was with some of the best in the business. Each morning, we checked for a storm's most vital ingredients – high "Cape" (convective available potential energy, or food for the storm) and shear-wind rotation – to decide an initial target for early afternoon, then homed in further as the weather information developed. Only by V C doing this can you be in the perfect position when the cap, a layer of cold air holding down the rotating moist air, bursts and the storm explodes into life. From then on, it was down to the spotters to position us close – but not too close – to the swirling mass of cloud that could just drop to form a tornado.
The day of the tornado looked good from the start. Our spotters had positioned us well the night before and it was a short drive to the initial target. After a long radar watch in Kimball, Nebraska, the cap was broken and we were off, new target La Grange, Wyoming. This time there was real confidence, a buzz of excitement.
Soon there was a tornado warning on the storm cell we were following. Hearts beating, we stood under a rotating mass of cloud. In the distance, a thick, solid wall cloud lowered and twice the funnel built, only to retract just feet from the ground. On the third time, it stuck. We had our first tornado.
It was about 10 miles away and heading directly towards us. Moving at around 30mph, it would be on us in around 20 minutes – but right now it was far from a violent destructive beast; it was a thing of beauty, sitting beneath a monstrous storm, cruising gently on the rolling plains, almost unreal.
Had it been going through a town, the rubble and debris it munched up would have created a far more fearsome sight, but here, other than the odd horse or cow – all of which fortunately escaped – there was little to interrupt the pure magnificence of this stunning natural phenomenon. Until, that is, it got close to us.
The Tornado Intercept Vehicle from Discovery's show later informed us that the ferocious winds spinning around this wide, rain-wrapped cone had whipped up to 125mph.
As it passed within a mile of where we were, the tornado drew deafening inflow winds across our sturdy Hummer, rocking it from side to side as we dived in for shelter.
The twister made a graceful departure, tightening up into a tall, slender, snaking white funnel tube before gently fading away to nothing. It had been a spectacular show, timed and placed to perfection. But the departing storm had more to show us as it continued on its way.
A few hours later, we raced along the rain-drenched highway, on the run from the new tornado produced by the supercell we'd seen before. Now, our hearts were beating 10 times as fast. "Oh, this is bad, man," said Gabriele, stating the obvious, as golf ball-sized hail started to fall. "We've got to go! We've got to go!"
We flew past semi-trailer trucks that would surely be clawed into the monster behind us, and although the technology we had at our disposal ensured we had everything under control, we only escaped disaster by a matter of minutes.
It's the gigantic supercells – alien motherships hovering just yards above the ground – that are perhaps the biggest draw. We saw just one tornado on our 10-day trip, yet the experience of being beneath these rotating beasts day after day, waiting for a tornado to drop, was unforgettable.
These days, if you can see a twister, you can chase it. But when a supercell storm starts chasing you – when you know it's there but you can't see where it is – that's when you get scared. And that's what gives you storm addiction.
Most tours start from Amarillo, Dallas or Oklahoma City.
British Airways (0844 493 0787; ba.com) and American Airlines (020-7365 0777; americanairlines.co.uk) fly direct to Dallas from Heathrow. Oklahoma can be reached from a range of UK airports via Newark with Continental (0845 607 6760; continental.com/uk), or from Heathrow via Atlanta with Delta (0845 600 0950; delta.com).
To reduce the impact on the environment, you can buy an "offset" through Abta's Reduce my Footprint initiative (020-3117 0500; www.reducemyfootprint.travel).
A leading storm-chasing tour company is Cloud 9 (001 405 323 1145; cloud9tours.com), which made it to the Wyoming tornado. Two-week tours cost $2,800 (£1,867) per person, including accommodation but not food or flights. Tours of 18 people are run in two vans and one suburban (station wagon).
Tradd Tours (traddstorm chasingtours.com) is also recommended, with two big vans. Two-week tours cost $3,199 (£2,133) per person, including accommodation but not food or flights.