Afilm featuring the "biggest tornado in history", one with wind speeds of more than 320 kilometre per hour, can seem like a far-fetched idea, but one that's perfect for movie mayhem. The thought of a gargantuan, more than 3km-long vortex of violent winds rotating in a corkscrew whirl, coming out of nowhere and whipping up everything in its wake - people, houses, 18-tonne trucks - can be pretty terrifying, after all.
Yet such a scenario isn't purely fictional. Indeed, soon after shooting finished on Into the Storm, a real-life tornado that was even larger than the massive EF5 tornado (the highest point on the Enhanced Fujita Scale used to rate tornadoes in the US and Canada) in the movie hit Oklahoma.
"The first person I gave [the script] to read about these different tornadoes and fire tornadoes, and said, 'This is so stupid, you are literally an idiot'," Into the Storm screenwriter John Swetnam recalls. "But the next time I sent it out, I included pictures from YouTube of these real things, and then it was, like, 'Oh … okay!'"
The new disaster thriller has inevitably been compared to Twister, the 1996 film starring Bill Paxton and Helen Hunt that famously features a cow sent flying by the strong winds. Twenty-five years on, Swetnam - Into the Storm is his first big studio film - wanted to make a disaster drama that encompassed modern-day elements such as "found footage", in an age where everything can be recorded on a phone.
The movie also fits into the growing genre of "cli-fi" films revolving around natural disasters and climatic perversions, and the people they affect.
"Everything happened really fast," says Swetnam, who wrote the first draft of the script in four days. "I knew exactly what the film was supposed to be. The challenge comes afterwards, when you have a movie that's actually going to be made, constantly working with the director, studio people, producers, giving everyone what they want but also doing your own thing."
With cinematographer-turned-director Steven Quale at the helm, the film stars The Hobbit's Richard Armitage (as Gary, a widower with two teenage sons), comedian-actor Matt Walsh (as Pete, an obsessive storm chaser), and Sarah Wayne Callies (as meteorologist Allison, who works with Pete). Their characters go on the run from furious twisters unleashed by a massive storm that is ravaging the fictional town of Silverton.
The cast members became unintended weather experts while researching their parts.
For example, Walsh looked at amateur videos online and used the unbridled enthusiasm for storm chasing depicted on YouTube to fuel his portrayal of Pete. "He's a guy who's going to lose all his money if he doesn't catch this storm," Walsh says of his film alter-ego. "He's spent his life building the perfect vehicle, one that can sit in the eye of a tornado and not be harmed. He wanted to feel the full force of Mother Nature, all at once."
For her part, Wayne Callies talks of having cold-called a professor of climatology and telling her "I need to turn into you in two weeks". Charged with portraying Pete's competent and confident colleague, "I had to very quickly learn about heat and humidity. That was the fun part of what we do. With every new job, you are immersed in a world you didn't know anything about before," she says.
Swetnam spent some of his childhood in Tennessee, where tornado warnings were a matter of course. Everyone had storm shelters. Everyone knew disaster could strike anytime. So when he was approached by producer Todd Garner to work on a tornado film, the scriptwriter immediately tapped into that sensibility.
"I knew the structure and visual style and characters that I wanted," he says. "Then we sent it to the meteorologists and all the other smart people. I just laid the fun groundwork, and then Steve [Quale] took it to this awesome level."
Like Swetnam, Quale grew up in a part of the US where tornadoes were a fact of life. "We used to go into the storm shelter in the basement and watch TV and wait it out. But as a kid, I always had that uneasy feeling of not knowing if the storm was going to come and destroy the buildings around us," the native of Madison, Wisconsin, says.
After he moved to Los Angeles, which lives with the spectre of earthquakes like much of the central US does with tornadoes, Quale further witnessed "how communities come together in these adverse situations of tragedy, and there's a bonding that happens. It was an experience I tried to put into the film as well."
However, when filming Into the Storm in Pontiac, Michigan, Quale found that weather conditions there simply didn't fit the picture. "Here we were making a movie about overcast cloud conditions as they form, and we were shooting in sunny Pontiac in the summer," the director says.
The filmmaker, who previously worked as Avatar's visual effects supervisor, employed a combination of digital effects and live-action shots to create the realism seen on screen. For example, much of what goes on when debris is flying, when there is driving rain and wind in the background, and when Armitage's character is almost flattened by a falling truck is "real": they are not digitally rendered. However, Quale did augment the shot footage with digital effects - adding larger debris that would be too dangerous to throw at the actors, and having vehicles fly in the background.
To add to the authenticity of the visuals, each cast member shot footage from his or her own vantage point that was used in the film. The end result is that the action scenes look strikingly realistic, putting audiences right in the action.
Quale believes the disaster film genre still has a lot of life left in it. "People are fascinated with the things that terrify them the most. It's just something about human nature. 'What would it be like if I was right inside the eye of a storm?' When you see a movie like this, you can do so in the safe confines of a theatre, knowing you will be okay. You can grab the hand of your date and live through it."
Into the Storm opens on Thursday