Factual error: When they are at Aunt Meg's the first time, they get word that a tornado has been spotted and somehow they already know its rating. Tornadoes get their ratings from the amount of damage they do. This is determined after the tornado is gone.
Other mistake: When the twister hits the drive in theater, the sirens are wailing, but nobody reacts. Only when Jo screams at the waitresses they start panicking and run. The movie is set in Oklahoma, smack in the middle of tornado alley. The people there know what the sirens mean, they sure don't need no out-of-town big-shots to tell them to get under cover.
Suggested correction: Sirens go off so many times that true Okies tend to ignore them. We might get nervous if the cable goes out.
Do true Okies also run screaming the second an out-of-town big-shot yells at them? Sorry but that argument just doesn't compute. People ignoring fair warning simply isn't a thing in the movie. The main plotline is people not getting warnings soon enough.
It's also possible that they did hear the siren, but unlike the people at the drive-in who could actually see the tornado tearing the screen apart, the people at the snack bar might not have been able to see it (especially with an awning over the windows). They were probably at most confused as to what was happening and it wasn't until Jo actually said to get underground that they realised it was real and was actually happening.
Really?! As I already wrote, the people in tornado alley know very well what the sirens mean. And they don't look confused or bewildered either.
Other mistake: When the Tree gets blown under the red truck and they get stuck on it. Why don't they ever put the truck in 4WD? You can see the front differential and 4x4 markings so the truck definately HAS 4WD. That particular year of truck doesn't even require you to get out and lock the hubs.
Suggested correction: Character mistake more than anything. In a panic situation you don't tend to think of the obvious solution. The other issue to is that even if the truck was in 4wd that it might not have been enough. Keep in mind that the rear tires did burnout on a few attempts so the issue wasn't that the wheels weren't stable on the ground but that the tree trunk might have been too big to get the wheels over it by driving across (especially from the angle they were at).
Stupidity: In the opening, it's surprising that Jo and her family have to actually go outside and run even a short distance to get to their cellar. Farm houses, especially in tornado prone areas like rural Oklahoma, would typically be built overtop of the cellar, which would be accessible from inside the house. Furthermore, Jo's cellar door seems to be secured with what seems to be little more than a latch much like those used for restroom stalls! Not very practical for a door intended to protect the interior from outdoor elements.
Suggested correction: Their storm cellar is made of an old septic tank, which is very common to do. It's half buried into the ground so it provides maximum protection, unlike under the house because an F5 tornado would simply rip the entire house away, removing all the protection the cellar would have had. Also the door has several latches, not just one.
A cellar under the house would likewise be buried into the ground, often more than halfway, so it would offer just as much protection, if not more. Looking at the scene again, the door has two latches, both the same size and woefully insufficient.
Continuity mistake: After the first tornado when Jo's truck is destroyed, you see Bill's truck with a shell on it. When their group is leaving the scene, the shell is gone and one of the Dorothys is in the bed. Where did the shell go?
Suggested correction: ANSWER; As some time elapses between the tornado aftermath and leaving the scene, there are plenty of reasons why the shell moved.
Plot hole: During the scene when Jo introduced the first Dorothy to Bill for the first time, you can see the blurry figure of Dusty and Dr Melissa holding hands in the background, which is super weird given she was annoyed by his presence at that point.
Suggested correction: Dusty is leading her to Dorothy, to let her see what they are working on. Obviously she doesn't mind being led there by him. He is eccentric and direct and she isn't used to that, but that doesn't mean she thinks he's annoying. Not even a character mistake.
Suggested correction: The scale back then was based on the size of the tornado, it's only more recently it is based on damage. So during the time of the movie, the scale was being used correctly for size not damage.
The Fujita scale was introduced in 1971 and was in use during the 90's when this film came out. The Fujita scale measured the damage caused by a tornado to man-made structures after ground or aerial surveys, it was not a measurement of tornado size (an F5 tornado is a tornado that's rated on the Fujita scale). It is true the Fujita scale was replaced by the enhanced Fujita scale in 2007, but that was only to align the ratings to the damage better, it did not change rating tornadoes from size to destructive powers.
Bishop73