Dear Tom,

Can you explain the “EF” designation for tornados and how it’s used to classify them based on velocity?

Doug Barnum, Homewood

Dear Doug,

The original Fujita tornado scale (F Scale) was devised by Tetsuya Fujita of the University of Chicago in 1971. The F-scale became the world standard for classifying wind speeds based on the damage caused by those winds. The scale was revised to the EF scale on Feb. 1, 2007, to more closely represent actual wind-speed damage. It is a six-point scale ranging from EF0 through EF5: EF0 tornadoes possess winds of 65-85 mph; EF1, 86-110 mph; EF2, 111-135 mph; EF3, 136-165 mph; EF4, 166-200 mph; and EF5, greater than 200 mph. Wind speeds in the original F-scale were much higher than needed to cause the respective degrees of damage described in the scale; as high as 318 mph for a top-end F5 tornado.