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.
Bishop73
27th Sep 2004
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