The Enhanced Fujita Scale or EF Scale, which became operational on February 1, 2007, is used to assign a tornado a 'rating' based on estimated wind speeds and related damage. When tornado-related damage is surveyed, it is compared to a list of Damage Indicators (DIs) and Degrees of Damage (DoD) which help estimate better the range of wind speeds the tornado likely produced. From that, a rating (from EF0 to EF5) is assigned.
The EF Scale was revised from the original Fujita Scale to reflect better examinations of tornado damage surveys so as to align wind speeds more closely with associated storm damage. The new scale has to do with how most structures are designed.
|EF Rating||3 Second Gust (mph)|
*** IMPORTANT NOTE ABOUT EF SCALE WINDS: The EF scale still is a set of wind estimates (not measurements) based on damage. Its uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to the 28 indicators listed below. These estimates vary with height and exposure. Important: The 3 second gust is not the same wind as in standard surface observations. Standard measurements are taken by weather stations in open exposures, using a directly measured, "one minute mile" speed.
The NWS is the only federal agency with authority to provide 'official' tornado EF Scale ratings. The goal is assign an EF Scale category based on the highest wind speed that occurred within the damage path. First, trained NWS personnel will identify the appropriate damage indicator (DI) [see list below] from more than one of the 28 used in rating the damage. The construction or description of a building should match the DI being considered, and the observed damage should match one of the 8 degrees of damage (DOD) used by the scale. The tornado evaluator will then make a judgment within the range of upper and lower bound wind speeds, as to whether the wind speed to cause the damage is higher or lower than the expected value for the particular DOD. This is done for several structures not just one, before a final EF rating is determined.
|1||Small barns, farm outbuildings||SBO|
|2||One- or two-family residences||FR12|
|3||Single-wide mobile home (MHSW)||MHSW|
|4||Double-wide mobile home||MHDW|
|5||Apt, condo, townhouse (3 stories or less)||ACT|
|7||Masonry apt. or motel||MAM|
|8||Small retail bldg. (fast food)||SRB|
|9||Small professional (doctor office, branch bank)||SPB|
|11||Large shopping mall||LSM|
|12||Large, isolated ("big box") retail bldg.||LIRB|
|14||Automotive service building||ASB|
|15||School - 1-story elementary (interior or exterior halls)||ES|
|16||School - jr. or sr. high school||JHSH|
|17||Low-rise (1-4 story) bldg.||LRB|
|18||Mid-rise (5-20 story) bldg.||MRB|
|19||High-rise (over 20 stories)||HRB|
|20||Institutional bldg. (hospital, govt. or university)||IB|
|21||Metal building system||MBS|
|22||Service station canopy||SSC|
|23||Warehouse (tilt-up walls or heavy timber)||WHB|
|24||Transmission line tower||TLT|
|26||Free standing pole (light, flag, luminary)||FSP|
|27||Tree - hardwood||TH|
|28||Tree - softwood||TS|
Other background information: