Dusty: "The Suck Zone." It's the point basically when the twister... Sucks you up. That's not the technical term for it, obviously.
During the big falling debris scene, Paxton and Helen Hunt are in the red truck. The truck hits a tractor. The impact damages the windshield, and it is clearly broken, but a second later the windshield is perfect and untouched.
According to the Special Effects documentary, the sound of the tornado was produced by recording a camel's moan and digitally slowing it down.