As towns across the central belt of the US known as tornado alley brace for high winds, Huw Cordey heads to Oklahoma to meet those who live to follow the "twisters" others dread.
Top storm chaser Roger Hill is giving a morning briefing to his 13 clients - a group of mostly middle-aged men.
The talk is much more serious than usual.
"We won't be going off-road today," he says, "because if we get stuck we could die. And when I say get back in the car, you get back in or we'll leave you behind.
"By the end of today," he continues, "people will have died and lives will have changed forever."
It all sounds a bit melodramatic but then Roger knows a few things about violent tornadic supercells, as he likes to call these weather systems.
His tornado count currently stands at 467 - and the fact that he is still alive to tell the tales is more than a little comforting to his clients.
Roger was just nine when he saw his first tornado, though his tally could have ended here.
One came through his hometown and carried away the family house - leaving an exhilarated Roger huddled in the cellar with his parents.
The right call?
Chasing days start slowly.
Roger has never seen a tornado before 1 o'clock, so mornings are all about getting into position.
Sitting in the passenger seat of his vehicle, Roger flicks continuously between computer weather models, which are being constantly updated via satellite.
Tornadoes can have a devastating impact on anything in their path
There are often several options on where to go, so making the right call is everything - especially today when big things are expected.
The forecast is so good that every storm chaser in the country seems to have descended on Oklahoma.
They all have laptops set up in their vehicles but I have a feeling that some storm chasers are keeping a closer eye on Roger - and what he is doing - than the weather models.
After an hour or two of driving, we stop for lunch at a fast food restaurant.
It is a familiar routine. The brand of hamburger is the only thing that changes.
The diet of a storm chaser is terrible.
While Roger ponders our next move, we sit waiting in the restaurant car park - another familiar routine.
They tell me tornado a hit their car side on
Suddenly, Roger shouts for everybody to get into the vans. The chase is on.
Thirty minutes later we are standing by the vehicles watching a supercell - the cyclonic storms that form tornadoes - sweep across the landscape.
We do not wait for long.
There is no sign of a tornado yet but the storm is moving at speed and Roger does not want to lose it.
"Back in," he shouts.
I am following behind in a pick-up truck, but Roger is not hanging around and at a junction I lose him.
So I fall in behind some other storm chasers.
There are low clouds twisting ominously above our heads. They look as if they might form a tornado at any minute but it is clear we have just missed one.
Half a dozen telegraph poles have been laid flat and at the side of the road we pass an SUV with all its windows blown out.
The occupants look dazed but otherwise OK.
Storm chasers monitor weather systems on laptops in their cars
Later, at my motel, I meet a group of storm chasers and they tell me a tornado hit their car side-on.
They are not exaggerating - another chaser shows me a video he took of the moment of impact.
There is still no sign of Roger but following other storm chasers I find myself on a highway driving through the core of a supercell.
The rain is coming down so hard I can barely see the front of the car.
The conditions are terrifying and in any other circumstance I would have pulled over but I do not want to get left behind.
Life and death
I am also worried about hail.
In storm chaser parlance, supercell hail is always the size of baseballs, or at the very least golf balls.
Either way the windscreen would end up on my lap.
I phone Roger on the mobile to find out what I should be doing.
His first response is not very comforting. "Where are you?" he shouts, "it's a matter of life and death."
Later I find out he could see a tornado forming on his computer models and thought it was heading straight for where he figured I was: a case of the storm chaser being chased by the storm.
Several hours later - and having failed to catch up with Roger - I arrive back in the motel.
On the local news channel, I see footage of the day's violent storms.
Fourteen tornadoes have been confirmed.
There is an aerial shot of a huge tornado with a cloud of debris at its base, then the devastating aftermath of its trail.
A trailer park, school and petrol station have been flattened. Six people have died.
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