The Enhanced Fujita scale (abbreviated as EF-Scale) rates tornado intensity based on the severity of the damage they cause. It is used in some countries, including the United States and France.[1] The EF scale is also unofficially used in other countries, including China.[2]
The scale has the same basic design as the original Fujita scale—six intensity categories from zero to five, representing increasing degrees of damage. It was revised to reflect better examinations of tornado damage surveys, in order to align wind speeds more closely with associated storm damage. Better standardizing and elucidating what was previously subjective and ambiguous, it also adds more types of structures and vegetation, expands degrees of damage, and better accounts for variables such as differences in construction quality. An "EF-Unknown" (EFU) category was later added for tornadoes that cannot be rated due to a lack of damage evidence.[3]
As with the Fujita scale, the Enhanced Fujita scale remains a damage scale and only a proxy for actual wind speeds. While the wind speeds associated with the damage listed have not undergone empirical analysis (such as detailed physical or any numerical modeling) owing to excessive cost, the wind speeds were obtained through a process of expert elicitation based on various engineering studies since the 1970s as well as from the field experience of meteorologists and engineers. Unlike the original Fujita scale and International Fujita scale, ratings on the Enhanced Fujita scale are based solely off the effects of 3-second gusts on any given damage indicator.[4]
The Enhanced Fujita scale replaced the decommissioned Fujita scale that was introduced in 1971 by Ted Fujita.[5] Operational use began in the United States on February 1, 2007, followed by Canada on April 1, 2013, who uses a modified version known as the CEF-scale.[6] [7] [8] [9] [10] It has also been in use in France since 2008, albeit modified slightly by using damage indicators that take into account French construction standards, native vegetation, and the use of metric units.[11] Similarly, the Japanese implementation of the scale is also modified along similar lines; the Japanese variant is referred to locally in Japan as the JEF or Japanese Enhanced Fujita Scale.[12] The scale is also used unofficially in other countries, such as China.[13]
The newer scale was publicly unveiled by the National Weather Service at a conference of the American Meteorological Society in Atlanta on February 2, 2006. It was developed from 2000 to 2004 by the Fujita Scale Enhancement Project of the Wind Science and Engineering Research Center at Texas Tech University, which brought together dozens of expert meteorologists and civil engineers in addition to its own resources.[14]
The scale was used for the first time in the United States a year after its public announcement when parts of central Florida were struck by multiple tornadoes, the strongest of which were rated at EF3 on the new scale.
In November 2022, a research paper was published that revealed a more standardized EF-scale was in the works. This newer scale is expected to combine and create damage indicators, and introduce new methods of estimating windspeeds. Some of these newer methods include mobile doppler radar and forensic engineering.[15]
In 2024, Anthony W. Lyza, Matthew D. Flournoy, and A. Addison Alford, researchers with the National Severe Storms Laboratory, Storm Prediction Center, CIWRO, and the University of Oklahoma's School of Meteorology, published a paper stating, ">20% of supercell tornadoes may be capable of producing EF4–EF5 damage".[16]
The seven categories for the EF scale are listed below, in order of increasing intensity. Although the wind speeds and photographic damage examples have been updated, the damage descriptions given are based on those from the Fujita scale, which are more or less still accurate. However, for the actual EF scale in practice, damage indicators (the type of structure which has been damaged) are predominantly used in determining the tornado intensity.
| Scale | Frequency[17] | Potential Damage | Example of damage | |||
|---|---|---|---|---|---|---|
| mph | km/h | |||||
| EFU | N/A | N/A | 3.11% | No surveyable damage.Intensity cannot be determined due to a lack of information. This rating applies to tornadoes that traverse areas with no damage indicators, cause damage in an area that cannot be accessed by a survey, or cause damage that cannot be differentiated from that of another tornado. | N/A | |
| EF0 | 65–85 | 105–137 | 52.82% | Minor damage.Well-built structures are typically unscathed, though sometimes sustaining broken windows, with minor damage to roofs and chimneys. Billboards and large signs can be knocked down. Trees may have large branches broken off and can be uprooted if they have shallow roots.[18] | ||
| EF1 | 86–110 | 138–177 | 32.98% | Moderate damage Damage to mobile homes and other temporary structures becomes significant, and cars and other vehicles can be pushed off the road or flipped. Permanent structures can suffer major damage to their roofs. | ||
| EF2 | 111–135 | 178–217 | 8.41% | Considerable damage Well-built structures can suffer serious damage, including roof loss, and the collapse of some exterior walls may occur in poorly built structures. Mobile homes, however, are destroyed. Vehicles can be lifted off the ground, and lighter objects can become small missiles, causing damage outside of the tornado's main path. Wooded areas have a large percentage of their trees snapped or uprooted. | ||
| EF3 | 136–165 | 218–266 | 2.18% | Severe damage A few parts of affected buildings are left standing. Well-built structures lose all outer and some inner walls. Unanchored homes are swept away, and homes with poor anchoring may collapse entirely. Trains and train cars are all overturned. Small vehicles and similarly sized objects are lifted off the ground and tossed as projectiles. Wooded areas suffer an almost total loss of vegetation and some tree debarking may occur. | ||
| EF4 | 166–200 | 267–322 | 0.45% | Devastating damage Well-built homes are reduced to a short pile of medium-sized debris on the foundation. Homes with poor or no anchoring are swept completely away. Large, heavy vehicles, including airplanes, trains, and large trucks, can be pushed over, flipped repeatedly, or picked up and thrown. Large, healthy trees are entirely debarked and snapped off close to the ground or uprooted altogether and turned into flying projectiles. Passenger cars and similarly sized objects can be picked up and flung for considerable distances. (Most recent example: 2024 Greenfield tornado) | ||
| EF5 | 201+ | 323+ | 0.05% | Incredible damage Well-built and well-anchored homes are taken off their foundations and they go into the air before obliteration. The wreckage of those homes is flung for miles and those foundations are swept completely clean. Cars, buses, trains, and airplanes can be rolled repeatedly or be thrown extremely far through the air. Large, steel-reinforced structures such as schools are completely leveled. Low-lying grass and vegetation are shredded from the ground. Trees are completely debarked and snapped. Very little recognizable structural debris is generated with most materials reduced to a coarse mix of small, granular particles and dispersed. Large, multiple-ton steel frame vehicles and farm equipment are often mangled beyond recognition and tossed miles away or reduced entirely to unrecognizable parts. Tall buildings collapse or have severe structural deformations. The official description of this damage highlights the extreme nature of the destruction, noting that "incredible phenomena can and will occur". (Most recent example: 2013 Moore tornado) | ||
The EF scale currently has 28 damage indicators (DI), or types of structures and vegetation, each with a varying number of degrees of damage (DoD). Each structure has a maximum DoD value, which is given by total destruction. Lesser damage to a structure will yield lower DoD values.[19] The links in the right column of the following table describe the degrees of damage for the damage indicators listed in each row.
| DI No. | Damage indicator (DI) | Maximum degrees of damage | |
|---|---|---|---|
| 1 | Small barns or farm outbuildings (SBO) | 8[20] | |
| 2 | One- or two-family residences (FR12) | 10[21] | |
| 3 | Manufactured home – single wide (MHSW) | 9[22] | |
| 4 | Manufactured home – double wide (MHDW) | 12[23] | |
| 5 | Apartments, condos, townhouses [three stories or less] (ACT) | 6[24] | |
| 6 | Motel (M) | 10[25] | |
| 7 | Masonry apartment or motel building (MAM) | 7[26] | |
| 8 | Small retail building [fast-food restaurants] (SRB) | 8[27] | |
| 9 | Small professional building [doctor's office, branch banks] (SPB) | 9[28] | |
| 10 | Strip mall (SM) | 9[29] | |
| 11 | Large shopping mall (LSM) | 9[30] | |
| 12 | Large, isolated retail building [Wal-Mart, Home Depot] (LIRB) | 7[31] | |
| 13 | Automobile showroom (ASR) | 8[32] | |
| 14 | Automobile service building (ASB) | 8[33] | |
| 15 | Elementary school [single-story; interior or exterior hallways] (ES) | 10[34] | |
| 16 | Junior or senior high school (JHSH) | 11[35] | |
| 17 | Low-rise building [1–4 stories] (LRB) | 7[36] | |
| 18 | Mid-rise building [5–20 stories] (MRB) | 10[37] | |
| 19 | High-rise building [more than 20 stories] (HRB) | 10[38] | |
| 20 | Institutional building [hospital, government or university building] (IB) | 11[39] | |
| 21 | Metal building system (MBS) | 8[40] | |
| 22 | Service station canopy (SSC) | 6[41] | |
| 23 | Warehouse building [tilt-up walls or heavy-timber construction] (WHB) | 7[42] | |
| 24 | Electrical transmission lines (ETL) | 6[43] | |
| 25 | Free-standing towers (FST) | 3[44] | |
| 26 | Free-standing light poles, luminary poles, flag poles (FSP) | 3[45] | |
| 27 | Trees: hardwood (TH) | 5[46] | |
| 28 | Trees: softwood (TS) | 5[47] |
The new scale takes into account the quality of construction and standardizes different kinds of structures. The wind speeds on the original scale were deemed by meteorologists and engineers as being too high, and engineering studies indicated that slower winds than initially estimated cause the respective degrees of damage.[48] The old scale lists an F5 tornado as wind speeds of 261-, while the new scale lists an EF5 as a tornado with winds above 200mph, found to be sufficient to cause the damage previously ascribed to the F5 range of wind speeds. None of the tornadoes in the United States recorded before February 1, 2007, will be re-categorized.
Essentially, there is no functional difference in how tornadoes are rated. The old ratings and new ratings are smoothly connected with a linear formula. The only differences are adjusted wind speeds, measurements of which were not used in previous ratings, and refined damage descriptions; this is to standardize ratings and to make it easier to rate tornadoes which strike few structures. Twenty-eight Damage Indicators (DI), with descriptions such as "double-wide mobile home" or "strip mall", are used along with Degrees of Damage (DoD) to determine wind estimates. Different structures, depending on their building materials and ability to survive high winds, have their own DIs and DoDs. Damage descriptors and wind speeds will also be readily updated as new information is learned.[19] Some differences do exist between the two scales in the ratings assigned to damage. An EF5 rating on the new scale requires a higher standard of construction in houses than does an F5 rating on the old scale. So, the complete destruction and sweeping away of a typical American frame home, which would likely be rated F5 on the Fujita scale, would be rated EF4 or lower on the Enhanced Fujita scale.[49]
Since the new system still uses actual tornado damage and similar degrees of damage for each category to estimate the storm's wind speed, the National Weather Service states that the new scale will likely not lead to an increase in the number of tornadoes classified as EF5. Additionally, the upper bound of the wind speed range for EF5 is open—in other words, there is no maximum wind speed designated.[4]
| EF0 | EF1 | EF2 | EF3 | EF4 | EF5 | |
|---|---|---|---|---|---|---|
| Weak | Moderate | Strong | Severe | Extreme | Catastrophic | |
| Weak | Strong | Violent | ||||
| Significant | ||||||
| Intense | ||||||
For purposes such as tornado climatology studies, Enhanced Fujita scale ratings may be grouped into classes.[50] [51] [52] Classifications are also used by NOAA's Storm Prediction Center to determine whether the tornado was "significant". This same classification is also used by the National Weather Service. The National Weather Service of Quad Cities use a modified EF scale wording, which gives a new term for each rating on the scale, going from weak to catastrophic.[53]
The table shows other variations of the tornado rating classifications based on certain areas.