Twister opens with a flashback from 1969, in which the young heroine Jo Harding's father yells that the TV weathercaster is tracking an F5 tornado. Actually, it wasn't until 1971 that the University of Chicago's Ted Fujita crafted his now-legendary Fujita tornado intensity scale. It uses observed damage patterns to rank tornadoes and estimate their wind speeds. The system links wind speeds and building damage, but there are many operational problems in actually trying to do so. Variations in construction also bring more headaches for the F-rater, according to Grazulis.
Every home is nailed together differently, anchored differently, built of different materials . . .
One damage surveyor may notice different elements of a complex damage scene than another surveyor, and thus assign a higher or lower rating accordingly. Grazulis found some striking discrepancies between the two data sets. In most cases, Grazulis opted for the lower rating, since damage claims are more often exaggerated than underplayed. The infamous flying cow in Twister just wouldn't do as an F-rating guide, says Grazulis. Since no research has been done on animals as missiles, all official ratings based on animal movements are pure guesswork.