When Chuck Doswell saw the storm that cut a path of destruction across the US state of Oklahoma on Monday, he knew in an instant that this storm was "off the scale".

For 30 minutes, Mr Doswell, a research meteorologist with the National Severe Storms Laboratory, rode along "with the monster".

He is a storm chaser, a person who either for research or personal curiosity trails these deadly storms.

The beast

Mr Doswell has never seen anything like Monday's storm

In his 27 years of chasing storms, he estimates that he has seen 150 to 200 tornadoes, and he said that the twister he saw on Monday "was the most awesome ... tornado that I've seen."

Tornadoes usually dissipate in 10 to 15 minutes. "This one just kept going and going," he said.

He followed the storm for 30 miles from its inception near the town of Chickasha to south of Oklahoma City, where it caused so much destruction.

When he first saw the storm, he immediately recognised it as a classic supercell, a massive thunderstorm.

The heart of the storm

Shortly after Mr Doswell arrived intercepted the storm on Monday, a large cone-shaped tornado dropped from the sky. It quickly dissipated.

"But I thought, 'this storm is not done,'" Mr Doswell said.

He followed the storm for 30 miles looking "right up into the heart of it", and he said it was clear that the storm would produce another tornado.

In that minute, a huge funnel touched down, and instead of dissipating, it grew.

'Something awful was about to happen'

Debris from destroyed homes flecked his windscreen

For miles, he followed the huge storm in the sparsely populated rural areas southwest of Oklahoma City, and he said, "I thought, I'm sure glad this beast is out in the middle of nowehere."

But then he noticed ragged bits of pink fibreglass insulation mixed with the rain pelting his windscreen. He thought: We may be in open country, but somebody got hammered.

The rain was full of debris - leaves, branches, shredded bits of paper, and mud. "Then I began to realise. We're getting close to Oklahoma City," Mr Doswell said.

He began to see power flashes as the storm hit power lines and transformers. "I realised something awful was about to happen."

The base of the tornado contained dark streaks meaning that it was hitting houses in the suburbs.

Downed power lines ended his chase

The tornado continued on to the east, but Mr Doswell's chase was over. The road was blocked with downed power poles and lines.

Mr Doswell takes three weeks vacation a year just to chase these awesome storms. In those three weeks, he counts himself "lucky" if he spends one hour chasing a tornado. On Monday, he saw two tornadoes in 30 minutes.

Unimaginable destruction

"If you haven't experienced a tornado, you can't possibly imagine what a storm like this can do," he said.

A tornado can sweep a well constructed home from its foundation and scatter the debris for miles. It can pick up train carriages.

The damage is beyond imagination

The freakish, horrific destruction left in the wake of these storms defies belief. "It's reflected in the kind of numb shock people have at what the storm did," Mr Doswell said.

Considering the destructive power of these storms, he said it is miraculous that so many people survive. Most people in the central Great Plains, which is also known as Tornado Alley, are reasonably well prepared.

He worries about tornadoes that strike people who do not live in Tornado Alley, who might not be as well prepared.

"A similar tornado outside of Tornado Alley could produce hundreds of casualties, easily," he said.