Why are some tornadoes rated with an F, and others with an EF?

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CEDAR RAPIDS, Iowa (KCRG-TV9) - Sharp-eyed readers of our tornado anniversary article on Wednesday may have noticed that the Oelwein, Charles City, and Washington tornadoes were rated as F5 and F3, yet the Parkersburg tornado in 2008 was rated EF5. Why the difference in the naming convention?

The Fujita Scale, which rates a tornado’s intensity based on the damage it causes, was developed by Dr. Ted Fujita of the University of Chicago, and was introduced in 1971. It went from F0 to F5, the latter being the most intense tornado causing complete destruction. Each rating level had an estimated wind speed range:

F0: 40-72 mph
F1: 73-112 mph
F2: 113-157 mph
F3: 158-206 mph
F4: 207-260 mph
F5: 261-318 mph

Since then, engineers and meteorologists have done much more research on tornadoes and the damage they cause. Better knowledge since then led to the Enhanced Fujita Scale, enacted in 2007. It accounts for more types of damage, including the type of structure and how well it was built, to give a more accurate representation of how strong a tornado really was. It turns out that the speed of wind that causes certain types of damage is lower than originally thought. The Enhanced Fujita Scale’s wind speed ranges are:

EF0: 65-85 mph
EF1: 86-110 mph
EF2: 111-135 mph
EF3: 136-165 mph
EF4: 166-200 mph
EF5: 200+ mph

This does not mean that an EF5 tornado is weaker than an F5 tornado because the estimated wind speed is less. It’s just that we have a greater understanding of what kind of wind it takes to sweep a well-built home away from its foundation, for example.

The Enhanced Fujita Scale has 28 distinct damage indicators, such as types of buildings (motel, car showroom, low-rise building, manufactured home, etc.), along with varying degrees of damage for each. That allows meteorologists to rate a tornado’s damage based on specific information.