It's hard to imagine a summer blockbuster with even less in the way of plot than JURASSIC PARK, but here it is. Bill (Bill Paxton) has abandoned the wild life of chasing tornadoes for a sedate berth as a weatherman and imminent marriage to therapist Melissa (Jami Gertz); he just needs wife Jo (Helen Hunt) to sign the divorce papers. Meanwhile, spunky Jo and her group of scrappy, pure-hearted tornado chasers are trying to beat the big, bad corporate-financed tornado chasers -- you can tell them by their glossy black vans -- to an important discovery about the structure of killer twisters. That's it. But no matter: We're here for the tornado effects, and they're stupendous, even if the lion's roar incorporated into the sound mix errs a tad on the side of overstatement (the twister is a monster -- we get it). Extreme-weather buffs, thrill-ride junkies and anyone else in search of mindless entertainment need look no further.