Revealing mistake: While driving the red truck through the rolling house, Dorothy is mounted on the back of the truck. There are some very sensitive and fragile instruments located on the top sides of Dorothy that stick up above the cab of the truck. These would certainly have been torn off while crashing through the walls of the house, turning Dorothy into a useless pile of junk.
Revealing mistake: When Bill and Jo are driving towards the first tornado together (arguing), it's clear there's no windshield in the red truck. There's no rear view mirror and it's perfectly clear. During the next few scenes, a rear view mirror appears and there is mud on the windshield around the wiper tracks.Ben's Mom
Revealing mistake: In the opening scene, where Jo is very young and her dad and mom are carrying her and running from the house to enter the storm shelter, the tornado is just 60 seconds or so from destroying their house and sucking Jo's dad away. If you look at the trees behind them as they are running, you can see the trees are barely moving from any wind at all. If a real tornado was that close, the trees would be half bent over from the 60-100+ mph wind.