TV weatherman Bill Harding is trying to get his tornado-hunter wife, Jo, to sign divorce papers so he can marry his girlfriend Melissa. But Mother Nature, in the form of a series of intense storms sweeping across Oklahoma, has other plans. Soon the three have joined the team of stormchasers as they attempt to insert a revolutionary measuring device into the very heart of several extremely violent tornados.
The year is 1969. In Oklahoma County, thunderstorms roll across an open plain, and in a remote farmhouse young Jo and her family are about to go to sleep, but her father is watching a tornado warning on TV. The TV warns that the imminent tornado may be an F5, the strongest known. Not long after the family reaches the storm cellar the huge twister hits, passing right over top of them & killing her father. 27 years later, Jo is now a storm scientist, trying to develop a tornado warning system with her soon-to-be-ex, Bill Harding. Multiple attempts fail for one reason or another, and their team sees a tremendous amount of damage & death. Then, one time, they find themselves In the damage path of a huge F5 tornado. Can they succeed in launching their test equipment, then escape the deadly storm in time?
When Bill goes to have Jo sign the divorce papers so he can marry his new girl, Melissa, Jo finds a collection of record breaking tornados and Bill follows along, soon his duties shift from divorcing Jo to helping her with record breaking technology to create a better warning system.
Bill and Jo Harding, advanced storm chasers on the brink of divorce, must join together to create an advanced weather alert system by putting themselves in the cross-hairs of extremely violent tornadoes.
- In June 1969, a young family takes shelter from an impending tornado. The father, in an attempt to save his family, tries to hold the storm cellar door down, but gets sucked into the tornado and killed. Watching in horror are the man's wife and his daughter Jo, who, despite the horror of the storm and losing her father, is entranced by the funnel.
The film cuts to the present day and meteorologists at the National Severe Storms Laboratory (NSSL) are discussing a building storm system over Oklahoma which could produce a record outbreak of tornadoes.
Meanwhile, retired storm chaser Bill Harding (Bill Paxton) and his fiancée Dr. Melissa Reeves (Jami Gertz) are heading out to meet Bills former storm-chasing team to get the final divorce papers from Bills soon to be ex-wife, Dr. Jo Harding (Helen Hunt) who, since the day her father died, has sworn to hunt down as many tornadoes as possible, not wanting the same fate to happen to someone else. Besides Jo, the team consists of the eccentric Dusty Davis (Philip Seymour Hoffman), Robert Rabbit Nurick (Alan Ruck) navigator, Laurence (Jeremy Davies) photographer, Joey (Joey Slotnick), Alan Sanders (Sean Whalen) Rabbits driver, Tim "Beltzer" Lewis (Todd Field), Haynes (Wendle Jospeher) who rides with Beltzer, and Jason "Preacher" Rowe (Scott Thomson).
Jo, who is still in love with Bill, tries to stall because she does not want the marriage to end. Jo then tells Bill she wanted him out on the field because his idea for a tornado-analyzing device called 'Dorothy' has been built. They will put it in the path of a tornado to measure it from inside. Four of the so-called "Dorothy" weather machines have been built. Haynes tells them of storm activity, and they head out. Bills rival team shows up, led by Dr. Jonas Miller (Cary Elwes) with his assistant Eddie (Zach Grenier).
According to Bill, Jonas is in the storm-chasing business "for the money, not the science." Bill sees Jonas giving an interview to some local reporters and finds out that Jonas has stolen his idea for the Dorothy weather machine, building his own version called D.O.T. 3, or Digital Orphagraphic Telemeter. Bill accuses him of stealing his idea, but Jonas says it was an "unrealized idea." Bill decides to stay with the team for one day in an attempt to beat Jonas.
Bill's team heads out and Bill and Jo have a frank discussion of their marriage. Beltzer notices a small tornado, an F1, touching down in a nearby field and alerts the team. Jo and Bill drive into a ditch to get in front of it, but cannot get out of the ditch as the tornado closes in. They crash into a small wooden bridge and take cover under it. Jo wants to see the tornado up close, but Bill stops her just as the tornado lifts Jo's truck off the ground. Jo's truck falls in front of Melissa, who is driving Bill's truck. She drives around it, narrowly missing a collision.
Bill comforts her as Jo inspects the damage and takes some of the sensors from the destroyed Dorothy 1 machine. Jonas' team shows up but is too late to see the storm and keeps driving. Jo, with no truck of her own, manages to convince Bill to use his new truck to haul the Dorothy machines.
Bill's team heads out again as Bill, Jo, and Melissa ride in his truck. Another tornado, a slightly larger F2, has touched down, and both Bill's team and Jonas's team are heading to intercept it. Bill believes the tornado will shift its track, and his team heads off on a back road. Bill soon drives onto a bridge and they are caught in some waterspouts, which spin the truck. The team arrives just after the incident and while Jo celebrates with the team, Melissa breaks down, questioning Bill's old lifestyle.
The team goes to visit Jo's aunt, Meg Greene (Lois Smith), in the nearby town of Wakita, Oklahoma to rest and eat. Meg tells Jo privately that Jo's marriage with Bill ended because, "He didn't keep his part of the bargain."
As the team is watching TV, it mentions an F3 tornado is active, and the team heads out. Bill and Jo drive together in his truck, and Melissa rides with Dusty in his converted schoolbus. They almost crash into Jonas' team in an attempt to beat them. Bill's team attempts to figure out where the tornado is because according to their computers, it is heading towards them on the same road. Bill and Jo realize it is over a hill, and they go through a hailstorm to find it. Upon finding the tornado, Bill and Jo try to set up Dorothy 2, but run out of time. A power pole falls on the truck, ruining Dorothy 2. The tornado then lifts back into the clouds. Jo attempts to gather the scattered sensors, but Bill, realizing that the tornado has not dissipated but is simply back-building, pulls her into the truck as the tornado drops once more.
They drive to a safe distance, where Jo jumps out of the truck and again attempts to gather the scattered sensors. She grows angry about Bill's attempt to stop her, but Bill tells Jo she is obsessed to succeed with Dorothy to prevent what happened to her family from happening again. He also tells her he still has feelings for her. Melissa and Jo's whole team hear their conversation over the CB radio.
That evening, Bill's team heads to a drive-in theater, where Jo signs the divorce papers, while Melissa is in a motel room across the road watching a weather report of more tornadoes nearby. Dusty is watching the radar. Both Melissa's TV and the TV at the concession stand lose their reception as Dusty warns Bill that an F4 tornado is heading right for them. Everyone takes shelter in the pit of a car mechanic's garage while Jo watches it approach, spellbound, much like she had when she was a girl when her father was killed, until Bill's shouting breaks her trance and she gets the theatre employees to take cover. The tornado obliterates the theater, destroying several of the team's vehicles and Preacher is hurt when he is hit in the head by a flying hubcap.
The tornado passes, and the team emerges to inspect the damage. Dusty looks at the radar to find that the same tornado is now heading directly for Wakita. Bill tells Melissa they are leaving to check on Aunt Meg, and Melissa peacefully breaks up with him, saying that she does not want to compete with his need to chase tornadoes. She tells him she is not at all upset about breaking up, knowing that their relationship would have ended sooner or later, and assures Bill that Jo needs him more.
Upon arriving in Wakita, they find the town is destroyed, and Jo realizes there had been no warning. Bill and Jo find Megs home on the verge of collapse. Upon entering, they find Meg pinned underneath a bookshelf. Jo and Bill rescue her and her dog Mose before the house collapses. Meg manages to escape the tornado with nothing more than "a bump on the head" and a broken wrist, and is taken to a hospital. Before leaving, she tells Jo that she needs to succeed to make sure what happened to Wakita doesn't happen again. Dusty listens to the radio, hearing that meteorologists are predicting rare F5 tornadoes. Jo comes up with a way to make Dorothy work while watching some wind chimes. She has Bill's team fabricate pinwheels out of aluminum cans, and attaches them to the sensors with screws to make them fly.
A few hours later, as dawn begins to break, Bill and Jo come alongside a huge, mile-wide F5 tornado in the countryside. They put Dorothy 3 on the road in front of the tornado and then back up, but the winds push Dorothy around, and then a tree knocks Dorothy 3 over, scattering the sensors. The storm turns toward Bill and Jo, and they attempt to drive away. They become stuck when a tree wedges underneath the back end of their truck. A tanker fuel truck is pushed along the road toward their truck by the tornado, and knocks them free before exploding. Bill drives around the wreckage through the fireball, narrowly avoiding catastrophe. Bill drives ahead of the tornado, dodging as it drops farm vehicles on the road in front of him. They end up driving through a small house that is rolled by the tornado onto the road.
As Bill and Jo drive away, Jonas and Eddie ride to intercept the tornado and place their D.O.T. 3 pack. Jo and Bill, noticing that Jonas is driving too close to the tornado, warn him to change course but he ignores them. Eddie wants to heed Bill's warning, but Jonas orders him to keep driving. The tornado hurls a section of a TV tower through their windshield, impaling Eddie. Both teams watch in horror as Jonas's truck is lifted up by the tornado and thrown into the ground where it explodes, killing both Eddie and Jonas.
Bill and Jo then conclude there is one last option left. They head toward a new intercept point, turn on Dorothy 4 without releasing it from its moorings on the truckbed, and then drive the truck straight at the tornado. With the truck on cruise control they jump out, letting it drive into the center of the tornado where it successfully deploys Dorothy 4.
The team starts to celebrate as the Dorothy sensors work, analyzing the inside of the tornado, but then notice the tornado shifting. Bill and Jo notice it as well and flee to a nearby farm. They first take cover in a barn, but it is filled with sharp metal tools. It destroys the barn, and they dodge debris as they run to take cover in a small outbuilding. They find metal pipes inside this shelter and tie themselves to the pipes with leather belts. The tornado destroys the structure, and they are pulled upside down while anchored to the pipes. They manage to see the inside of the F5 tornado as it passes over them. It is filled with lighting and a smaller tornado in the core. Seconds later, the entire storm dissipates, and the family from the farm comes out of their underground storm shelter and observe their damaged farm. Bill and Jo debate who will run the lab and who will analyze the new data from Dorothy while the rest of the team arrives. The movie ends with Bill & Jo reconciling their relationship with a kiss, while the team celebrates their accomplishment.