Factual error: In the begining when Jo's dad is bringing the family downstairs and say's "TV says it's big, might be an F-5" That scene was set in 1969. In reality he would not have known anything about an F-5 or any tornado with an F rating because the Fujita scale was not developed until 1971.
Factual error: Paxton and Hunt drive their truck toward the twister in a corn field, they jump out of the truck and then start running for it. Have you ever run in a corn field? You can't run in a corn field that has stalks that high, they would cut you to shreds. They would have been bleeding on the faces and hands and arms if they were wearing short sleeve shirts. If you enter a corn field, you must move with the rows - you cannot cross rows because the stalks are just like small trees and they are maybe six inches apart.
Factual error: We all know that when any tornado is on the ground and/or near moving towards us, things get blown around, like trees, grass, and other things. There are two things that I found that didn't look right. It's in the scene when the F-5 tornado is chasing Bill and Joe to the Barn. First the grass and cornfield are moving but not the trees. And second, when the tornado blows away the brown picket fence we see most of the pickets shoot upwards, which is impossible because they are nailed to horizontal boards. It would either take a far stronger wind than they're currently in to rip the pickets straight up, or the pickets were made out of far cheaper wood than they appear to be.
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Factual error: In the last scenes when Bill and Jo are in the shed with the water pipes, the shed is torn apart by wind as well as flying debris at hundreds of miles per hour. I have watched the scene numerous times and there is not so much as a scratch on their faces. Even if they lived, they would have been battered and bloody from debris. Regardless if tornadoes do weird things, the debris ripped the shed apart, which is stronger than a human body.
Factual error: Near the beginning, when we see Bill and Jo in Jo's truck driving in an off-road ditch being "chased" by a tornado, there is a shot where we see the tornado dismantle a barn. In real life, you wouldn't be able to see it dismantle the barn board by board. The tornado would actually cover the barn, and when it leaves, you would see the barn in desolation.
Factual error: In the scene when Bill and Joe are about to deploy Dorothy 2, we see that the tornado (F-2 I believe) rips out an entire row of power poles high into the sky with the power lines still attached to the poles straight from the ground. In real life, when a tornado runs over power poles, it would only knock them down.
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Factual error: When the team is attempting to intercept the second tornado, Bill floors the gas pedal in the Dodge Ram after Jo expresses disgust at how slow he's driving. The next shot shows the dashboard, where the speedometer moves from 50-70 MPH, the engine is heard accelerating in the background, but the tachometer stays around 1500 RPM. The truck is an automatic and so it would have downshifted when Bill pressed the accelerator to the floor, and therefore revved much higher.