Tornado Ratings

Tornadoes were originally rated on the Fujita Scale, named for its inventor, University of Chicago meteorologist T. Theodore Fujita. Fujita created the scale, based on the wind speed and type of damage caused by a tornado, in 1971. There were six levels on the original scale:

Level
Wind Speed
Possible Damage
F0 40 - 72 mph Light damage: Tears branches from trees; rips shallow-rooted trees from the ground; can damage sign-posts, traffic signals and chimneys
F1 73 - 112 mph Moderate damage: Roofing materials and vinyl siding can be displaced; mobile homes are highly vulnerable and can easily be knocked from the foundation or toppled; motorists can be sent careening off road and possibly flipped over
F2 113 - 157 mph Considerable damage: Well established trees are easily uprooted; mobile homes are dessimated; entire roofs can be ripped off houses; train cars and trucking hauls are knocked over; small objects become dangerous missiles
F3 158 - 206 mph Severe damage: Forests are destroyed as a majority of trees are ripped from the ground; entire trains are derailed and knocked over; walls and roofs are torn from houses
F4 207 - 260 mph Devastating damage: Houses and other small structures can be razed entirely; automobiles are propelled through the air.
F5 261 - 318 mph Incredible damage: Cars become projectiles as they are hurled through the air; entire houses are completely destroyed after being ripped from the foundation and sent tumbling into the distance; steel-reinforced concrete structures can be seriously damage

Source: NOAA

In February, 2007, the Fujita Scale was replaced by the Enhanced Fujita Scale. The new "EF" scale is similar to its predecessor. It classifies tornadoes into six different categories (EF0 through EF5 instead of F0 through F5). Where the EF scale differs, however, is in the number of criteria used to assess a tornado's level of damage. First, there are damage indicators -- objects that can be damaged in the tornado. These are classified from 1 (small barns) to 28 (softwood trees). Each damage indicator can also experience varying Degrees of Damage (DOD). Each DOD corresponds to estimated wind speeds.

For example, a motel has 10 degrees of damage, ranging from broken windows (3) to the collapse of most of the roof (6) to complete destruction of the buildling (10). If a motel's windows are broken, but it doesn't sustain more extensive damage, the estimated lowest possible wind speed is 74 MPH, while the estimated highest possible speed is 107 MPH. Meteorologists average of these speeds, meaning the expected wind speed is 89 MPH. An examination of the EF Scale reveals that 89 MPH falls into the EF1 category (86-110 MPH), so the tornado is classifed as an EF1. For more information about the EF scale, see the official NOAA website.

­ For more information on tornadoes and related topics, check out the links on the next page.