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Enhanced Fujita scale
Enhanced Fujita scale
Enhanced Fujita scale
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Enhanced Fujita Scale
EFU Unknown No surveyable damage
EF0 65–85 mph Light damage
EF1 86–110 mph Moderate damage
EF2 111–135 mph Considerable damage
EF3 136–165 mph Severe damage
EF4 166–200 mph Devastating damage
EF5 >200 mph Incredible damage
The National Weather Service's arrow showing the EF scale. This includes a description word for each level of the scale.

The Enhanced Fujita scale (abbreviated EF-Scale) is a scale that rates tornado intensity based on the severity of the damage a tornado causes. It is used in the United States and France, among other countries.[1] The EF scale is also unofficially used in other countries, including China and Brazil.[2][3] The rating of a tornado is determined by conducting a tornado damage survey.

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.[4]

As with the Fujita scale, the Enhanced Fujita scale is a damage scale and only an estimate for actual wind speeds. While the wind speeds associated with the damage listed did not and have not undergone empirical analysis (such as detailed physical or any numerical modeling) due to expensive costs, the wind speeds were obtained through a process called expert elicitation, which was 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.[5]

History

[edit]

The Enhanced Fujita scale replaced the decommissioned Fujita scale that was introduced in 1971 by Ted Fujita.[6] 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.[note 1][7][8][9][10][11] 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.[12] In Brazil, the EF Scale is used by the Reporting Platform and Voluntary Network of Severe Storm Observers (PREVOTS) since June 2018.[3] 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.[13] The scale is also used unofficially in other countries, such as China.[14]

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.[15]

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 wind speeds in tornadoes. Some of these newer methods include mobile doppler radar and forensic engineering.

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]

Parameters

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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.[5]

Scale Wind speed estimate[17] Frequency[18] 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.[4] 		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 may be uprooted if they have shallow roots.[19] 		EF0 damage example--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.
EF1 86–110 138–177 32.98% Moderate damage.
Damage to mobile homes and other temporary structures becomes significant, and cars and other vehicles may be pushed off the road or flipped. Permanent structures can suffer major damage to their roofs. 		EF1 damage example--There is 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. 		EF2 damage example--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. 		EF3 damage example--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.
EF5 201+ 323+ 0.05% Incredible damage.
Well-built and well-anchored homes are swept cleanly off their foundations and obliterated. 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, dispersed mix of small, granular particles. 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 suffer severe structural deformation. The official description of this damage highlights the extreme nature of the destruction, noting that "incredible phenomena can and will occur". 		EF5 damage example--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. 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".

Damage indicators and degrees of damage

[edit]

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.[20] 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[21]
2 One- or two-family residences (FR12) 10[22]
3 Manufactured home – single wide (MHSW) 9[23]
4 Manufactured home – double wide (MHDW) 12[24]
5 Apartments, condos, townhouses [three stories or less] (ACT) 6[25]
6 Motel (M) 10[26]
7 Masonry apartment or motel building (MAM) 7[27]
8 Small retail building [fast-food restaurants] (SRB) 8[28]
9 Small professional building [doctor's office, branch banks] (SPB) 9[29]
10 Strip mall (SM) 9[30]
11 Large shopping mall (LSM) 9[31]
12 Large, isolated retail building [Wal-Mart, Home Depot] (LIRB) 7[32]
13 Automobile showroom (ASR) 8[33]
14 Automobile service building (ASB) 8[34]
15 Elementary school [single-story; interior or exterior hallways] (ES) 10[35]
16 Junior or senior high school (JHSH) 11[36]
17 Low-rise building [1–4 stories] (LRB) 7[37]
18 Mid-rise building [5–20 stories] (MRB) 10[38]
19 High-rise building [more than 20 stories] (HRB) 10[39]
20 Institutional building [hospital, government or university building] (IB) 11[40]
21 Metal building system (MBS) 8[41]
22 Service station canopy (SSC) 6[42]
23 Warehouse building [tilt-up walls or heavy-timber construction] (WHB) 7[43]
24 Electrical transmission lines (ETL) 6[44]
25 Free-standing towers (FST) 3[45]
26 Free-standing light poles, luminary poles, flag poles (FSP) 3[46]
27 Trees: hardwood (TH) 5[47]
28 Trees: softwood (TS) 5[48]

Differences from the Fujita scale

[edit]

The Enhanced Fujita 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.[49] The old scale lists an F5 tornado as wind speeds of 261–318 mph (420–512 km/h), while the new scale lists an EF5 as a tornado with winds above 200 mph (322 km/h), 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, were re-categorized during and after the transition to the EF Scale.

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.[20] 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 probably be rated EF4 or lower.[50]

Since the EF Scale 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 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.[5]

Rating classifications

[edit]
Tornado rating classifications
Organization EF0 EF1 EF2 EF3 EF4 EF5 Cit.
NWS Quad Cities, IA/IL Weak Moderate Significant Severe Extreme Catastrophic [51]
NWS Weak Strong Violent [52]
NWS Significant [52]

For purposes such as tornado climatology studies, Enhanced Fujita scale ratings may be grouped into classes.[53][54][55] The National Weather Service classifies EF0 and EF1 as weak, EF2 and EF3 as strong, as EF4 and EF5 as violent.[52] The National Weather Service also uses the EF scale to classify tornadoes with a rating of EF2 and greater as significant.[52] The National Weather Service Quad Cities, Iowa/Illinois uses a modified EF scale wording, which gives a new term for each rating on the scale, going from weak to catastrophic.[51]

See also

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Notes

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References

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Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Enhanced Fujita scale

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from Grokipedia
The Enhanced Fujita scale (EF Scale) is a standardized system for rating based on the severity of damage inflicted on 28 specific damage indicators, such as one- or two-family residences, schools, and hardwood trees, which correspond to estimated 3-second gust wind speeds. Developed as an update to the original created by Tetsuya Theodore Fujita in 1971, the EF Scale was recommended by a multidisciplinary team of engineers and s in 2006 and officially implemented by the (NWS) on February 1, 2007, to provide more precise and consistent assessments. The original Fujita scale estimated tornado wind speeds from damage but faced limitations, including reliance on fewer damage types and higher assigned wind speeds that often overestimated actual gusts. The EF Scale addresses these by incorporating eight degrees of damage per indicator and calibrating to modern engineering standards for wind resistance. This refinement allows for better correlation between observed destruction and meteorological data, aiding in improved forecasting, warning systems, and post-event analysis by the NWS and . Tornado ratings range from EF0 (weakest) to EF5 (strongest), with no upper limit on EF5 winds, emphasizing that the scale measures structural impact rather than direct wind measurements, which are rare due to the dangers of close-range .
EF Rating3-Second Gust Wind Speed (mph)Expected Damage Description
EF065–85Light damage: Peels shingles off roofs, breaks branches, uproots shallow-rooted trees, damages signboards.
EF186–110Moderate damage: Removes roofs and siding, breaks large branches, uproots most trees.
EF2111–135Considerable damage: Tears off roofs, debarks trees, turns vehicles, collapses mobile homes.
EF3136–165Severe damage: Destroys well-constructed homes, trains off tracks, .
EF4166–200Devastating damage: Levels well-built homes, tosses vehicles long distances, ground scours.
EF5>200Incredible damage: Sweeps strong-frame homes from foundations, deforms large objects like steel beams.
The scale's adoption has led to more accurate historical comparisons of tornado events, though challenges persist in surveying remote or urban areas where damage indicators vary.

History and Development

Origins in the Fujita Scale

The Fujita scale, also known as the F-scale, was developed by Dr. Tetsuya Theodore Fujita, a meteorologist at the University of Chicago, in 1971 as a tool for retrospectively estimating tornado intensity based on the damage inflicted on human-built structures and natural features like vegetation. This scale emerged in the aftermath of the devastating F5-rated Lubbock, Texas, tornado on May 11, 1970, which killed 26 people and caused extensive urban destruction, prompting Fujita to create a standardized method for analyzing post-tornado damage to better understand wind speeds and improve future forecasting and warnings. The original methodology involved correlating observed damage patterns with estimated three-second gust wind speeds across six categories, from F0 (gale, 40–72 mph) to F5 (incredible, 261–318 mph), using approximately 12 types of damage indicators such as well-constructed houses, softwood trees, and utility poles to gauge the minimum wind required for specific levels of destruction. Fujita's scale was first applied operationally during the analysis of the April 3–4, 1974, Super Outbreak, a historic event producing 148 tornadoes across 13 states, where it helped classify multiple F4 and F5 storms and revealed insights into multiple-vortex structures. The National Weather Service (NWS) formally adopted the F-scale in 1973 for official tornado ratings, marking a shift from prior informal assessments and enabling consistent documentation in the national tornado database. Early applications highlighted the scale's utility in bridging the gap between lower-end wind scales like the and extreme speeds approaching Mach 1, but also exposed key limitations, including frequent overestimation of wind speeds due to uncalibrated damage-wind correlations and a failure to account for variations in construction quality or materials over time. Additionally, the reliance on subjective visual surveys often led to inconsistent ratings, as assessors lacked detailed guidelines for interpreting damage under diverse conditions, such as partial failures or non-standard buildings. These shortcomings, particularly the absence of adjustments for evolving building standards since the 1970s, underscored the need for refinements, which later informed the development of the Enhanced Fujita scale.

Creation of the Enhanced Scale

The development of the Enhanced Fujita (EF) scale began in 2000 as an initiative led by the (NWS) in partnership with the National Severe Storms Laboratory (NSSL) and a panel of engineering and meteorological experts, aimed at refining tornado intensity estimates through advanced aerodynamic research to overcome inaccuracies in the original Fujita scale's wind speed correlations. Central to the effort were contributions from Texas Tech University's Wind Science and Engineering Center, where a multidisciplinary team, including wind engineers like James R. McDonald and meteorologists such as storm chaser Warren Faidley, conducted forums and expert consultations to identify shortcomings in damage assessment. The project timeline spanned engineering analyses and iterative refinements from 2000 through 2006, with a key Enhancement Forum held in March 2001 to gather input from 20 specialists on damage-wind relationships, leading to a final recommendation submitted to the NWS in June 2004. The scale was officially implemented for public use on February 1, 2007, exclusively in the United States to standardize ratings. Major enhancements focused on precision in wind estimation and damage evaluation: the EF scale adopted 3-second gust speeds—aligning with contemporary meteorological standards—in place of the original's fastest-mile winds, while expanding from the original scale's roughly 6-12 informal damage descriptions to 28 formalized damage indicators (DIs), each with up to 8 degrees of damage (DOD) levels for more granular analysis. This structure allows for estimated wind speeds ranging from 65 mph (EF0 threshold) to over 200 mph (EF5), providing a more reliable framework for rating based on observed structural and environmental destruction. The inaugural application of the EF scale occurred in early 2007, with notable early ratings including the March 1 tornado in , assessed as an EF4 based on severe damage to well-constructed buildings and schools.

Subsequent Updates and Revisions

In 2022, revisions to the Enhanced Fujita (EF) scale were incorporated based on collaborative research involving meteorologists, engineers, and the (ASCE). These updates integrated new findings on vulnerabilities, vegetation resistance to wind loading, and failure modes in metal building systems, adding detailed descriptors for the latter to address gaps in assessing industrial and agricultural structures. Notably, the revisions refined thresholds for EF4 and EF5 ratings by adjusting expected 3-second gust wind speeds at select DOD levels, such as elevating the minimum for complete debarking of hardwood trees in EF5 scenarios to over 200 mph. These enhancements, balloted through the ASCE/SEI standards process by mid-2022, represented data-driven refinements to boost rating accuracy across diverse damage scenarios without altering core wind speed ranges. As of 2025, efforts continue toward formal standardization of the EF scale through the forthcoming ASCE/SEI/ standard on estimation in tornadoes, incorporating additional methods and contextual for assessments. These evolutions address limitations in coverage of contemporary building practices, improving reliability of intensity estimates while maintaining the six-category framework. For example, the June 20, 2025, Enderlin, , tornado was rated EF5—the first such rating in the U.S. since 2013—based on extensive debarking of trees and structural devastation under the refined guidelines.

Methodology and Parameters

Assessing Tornado Damage

The (NWS) employs a structured process to assess damage for assigning Enhanced Fujita (EF) scale ratings, focusing on the highest observed damage to estimate maximum 3-second gust wind speeds along the 's path. This evaluation is conducted through ground and aerial surveys, typically initiated within 12 to 48 hours after the event when safety conditions permit, to capture fresh evidence before further degradation or human intervention alters the scene. These surveys prioritize the worst-case damage indicators to determine the overall rating, ensuring the EF category reflects the most intense winds encountered. Multidisciplinary teams, including meteorologists, structural engineers, and damage assessment experts, carry out these surveys to provide a comprehensive analysis of structural and environmental impacts. Leadership is typically provided by Warning Coordination Meteorologists (WCMs), who coordinate with local and consultants to ensure accurate and consistent evaluations. Ground surveys involve on-site inspections of affected areas, while —using aircraft or helicopters—helps map broader paths in expansive or inaccessible regions. The assessment begins with identifying the tornado's path length, width, and track using pre-event data, eyewitness reports, and post-event or video footage to delineate the affected area. Survey teams then select representative segments of along this path, focusing on well-constructed buildings and natural features to avoid underestimating intensity due to poor-quality structures. For each segment, teams apply damage indicators (DIs) and corresponding degrees of (DOD) to gauge expected wind speeds, adjusting ratings based on contextual factors such as variations, quality, the tornado's forward speed, presence of multiple vortices, and whether it formed from non-supercell processes. Validation incorporates high-resolution , georeferenced videos, and radar-derived motion estimates to corroborate visual findings and rule out non-tornadic causes. Since around , NWS surveys have increasingly integrated unmanned aerial systems (drones) for hard-to-reach or hazardous areas, such as dense forests or debris-strewn zones, allowing teams to capture detailed without risking personnel . Drone footage, often provided in collaboration with local , supplements ground data to refine path mapping and damage segmentation. Preliminary ratings are issued via Public Information Statements during or shortly after surveys, with final EF classifications compiled and published in monthly Storm Data reports for archival and research purposes.

Damage Indicators and Degrees of Damage

The Enhanced Fujita (EF) scale utilizes 28 Damage Indicators (DIs), which categorize various types of structures and vegetation susceptible to tornado damage, to provide a standardized framework for evaluating structural integrity. These DIs encompass 23 built elements, ranging from small barns and farm outbuildings to high-rise buildings and transmission line towers, and 5 natural features, including grass, crops, billboards, softwood trees, and hardwood trees. Each DI is associated with up to 8 Degrees of Damage (DODs), describing progressive levels from the onset of visible damage—such as loose roof shingles or broken branches—to total destruction, like complete dispersal of a structure or denudation of trees. This system allows meteorologists to match observed damage to specific DOD thresholds, facilitating consistent assessments across diverse environments. Introduced in 2007, the DI framework replaced the original Fujita scale's limited 12 indicators, offering greater precision by incorporating engineering-based descriptions tailored to construction types and materials. These DIs ensure the scale remains adaptable to evolving building practices and environmental factors. As of 2025, updates to add new DIs, such as for utility poles and low-rise commercial buildings, are under development by the ASCE/SEI/AMS but have not yet been implemented. In applying the DIs and DODs during tornado surveys, forecasters identify the dominant DI within a path segment—such as residences or trees—and assign the highest applicable DOD based on the most severe, representative observed, while considering deviations like substandard or shielding effects from nearby objects. For instance, under DI 1 (small barns or farm outbuildings), DOD 8 describes complete dispersal of the structure, with all components swept away and the foundation potentially scoured, indicating extreme winds. Similarly, for DI 23 (softwood trees), DOD 6 involves more than 75% of trees being debarked, with 75% or more of the bark removed on at least 50% of affected trees, highlighting the scale's utility in quantifying vegetative scour. This methodical selection of the uppermost DOD for the primary DI helps derive a reliable EF rating for the segment without overemphasizing isolated anomalies.

Wind Speed Estimation

The Enhanced Fujita scale estimates tornado intensity by correlating observed degrees of damage (DOD) across various damage indicators (DI) to ranges of 3-second gust wind speeds, measured at 10 meters (33 feet) above ground level in open terrain. For each DI/DOD combination, engineers assign a lower-bound, expected, and upper-bound wind speed range based on the structural failure thresholds required to produce that damage level; for instance, minor peeling of roof shingles on a well-constructed frame home corresponds to an expected 3-second gust of 70-80 mph, falling within the EF0 category (65-85 mph). These estimates form the core formula for rating, where the tornado's overall EF rating is determined by the highest expected wind speed from the most severe DOD observed along its path. Wind speed estimation relies on engineering models derived from wind tunnel testing, computational fluid dynamics, and structural analysis to simulate how tornado winds interact with buildings and objects, ensuring the assigned speeds reflect realistic failure modes rather than speculative values. A panel of meteorologists, engineers, and wind experts developed these models, drawing on data from controlled experiments and post-tornado forensic investigations to quantify the wind forces needed for specific damage, such as roof loss or wall collapse. The methodology aligns with ASCE 7 standards for minimum design loads on buildings, incorporating factors like exposure category and topographic effects; surveyors qualitatively adjust expected speeds for site-specific conditions, such as construction quality or shielding. This approach was refined in the 2007 implementation of the EF scale, which shifted from the original Fujita scale's fastest-one-mile winds to 3-second gusts using the Durst curve for conversion, significantly reducing overestimation of high-end winds by aligning them more closely with observed —lowering thresholds for EF3-EF5 by approximately 20-30% compared to prior estimates. Boundary adjustments define category thresholds using the lower bound of the expected wind range; an EF3 rating requires at least 136 mph, while EF5 has no upper limit and starts above 200 mph, allowing for extreme events without artificial caps. Ongoing research as of 2025, including advanced and simulator tests, is informing a forthcoming ASCE/SEI/ Wind Speed Estimation in standard to potentially refine estimates for violent , but current thresholds remain unchanged.

Rating Classifications

EF Scale Categories

The Enhanced Fujita (EF) scale classifies into six categories, from EF0 to EF5, based on estimated 3-second gust derived from observed . These categories reflect increasing levels of potential destruction, with ratings assigned to the segment of the tornado path exhibiting the most intense . The following table summarizes the official EF scale categories, their corresponding wind speed ranges, and qualitative damage intensity descriptors:
EF Rating3-Second Gust Wind Speed (mph)Damage Intensity
EF065–85Light
EF186–110Moderate
EF2111–135Considerable
EF3136–165Severe
EF4166–200Devastating
EF5>200Incredible
General damage profiles vary by category but are assessed using 28 specific damage indicators, such as well-constructed homes, mobile homes, and trees. For instance, an can peel roofs from well-constructed homes, uproot large trees, and destroy mobile homes, while an can debark trees, sweep well-constructed homes clean from their foundations, and scour pavement from roads. The overall rating for a tornado is determined by the highest degree of damage along its path, ensuring the classification captures peak intensity rather than average effects. Since the EF scale's implementation in 2007, approximately 77% of rated U.S. tornadoes have fallen into the EF0 or EF1 categories, reflecting the prevalence of weaker events. Post-2007 ratings have been applied conservatively to prevent inflation of intensities compared to the original Fujita scale, with stricter criteria contributing to fewer high-end classifications. No EF6 category has been proposed or adopted, as the EF5 threshold remains open-ended to encompass all winds exceeding 200 mph without needing further subdivision. A recent example is the June 20, 2025, tornado near Enderlin, North Dakota, rated EF5 with winds over 210 mph based on extreme ground scouring and structural devastation.

Examples of Rated Tornadoes

The in , which occurred on , stands as a benchmark for EF5-equivalent damage under the original , later aligned with Enhanced Fujita criteria. Mobile measurements captured wind speeds of approximately 301 mph (484 km/h) near the tornado's core, the highest reliably recorded for any tornado. Ground surveys revealed extreme structural devastation, including well-constructed homes reduced to bare slabs with foundations swept clean (Degree of Damage 8 for single-family residences) and numerous hardwood trees debarked and denuded, indicators that would correspond to EF5 winds exceeding 200 mph under current methodology. This event killed 36 people and caused over $1 billion in damage, underscoring the scale's application in retroactively assessing violent . The 2011 Joplin, Missouri, tornado on May 22 exemplifies EF5 rating through meticulous post-event surveys emphasizing vegetation and building failures. assessments identified a 6-mile path of EF5 damage where asphalt shingles were stripped from roofs, vehicles were thrown significant distances, and large trees were completely debarked with only stubs remaining, corresponding to Degree of Damage thresholds for softwood and hardwood trees at EF5 levels. Well-engineered structures, such as portions of Saint John's Hospital, experienced total obliteration with foundations displaced, while over 550 homes were completely destroyed, justifying estimated winds over 200 mph. This tornado resulted in 158 fatalities and $2.8 billion in damages, highlighting how damage indicators like debarked trees and swept foundations drive high-end ratings. In contrast, the 2013 El Reno, Oklahoma, tornado on May 31 illustrates how radar data informs but does not override ground-based EF ratings. Despite mobile detecting winds up to 296 mph (476 km/h) and a path width exceeding 2.6 miles—the widest on record—the official rating was EF3 based on surveyed damage to 135 outbuildings and sparse structures, where most failures aligned with winds of 136–165 mph, such as roofs removed and walls collapsed but foundations intact. Limited high-end indicators, like minor tree debarking in isolated spots, prevented an upgrade, emphasizing the Enhanced Fujita scale's reliance on verifiable damage over alone. The event killed eight, including storm chasers, and damaged rural areas without widespread EF4/EF5 structural obliteration. The 2025 Enderlin, North Dakota, tornado on June 20 marked the end of a 12-year "EF5 drought," upgraded to EF5 on October 6, 2025, after detailed reanalysis—the first such rating since 2013 and the 60th overall since 1950. Surveys revealed peak winds exceeding 210 mph (338 km/h), supported by forensic engineering on a derailed where 33 fully loaded grain hopper cars were tipped over and an empty tanker car lofted 475 feet (145 m), a damage indicator exceeding EF5 thresholds. At Farmstead #2 along Highway 46, a well-built home suffered complete destruction with its foundation swept clean (Degree of Damage 8), debris scattered downwind, and surrounding hardwood trees debarked with root balls displaced, confirming violent winds. Additional indicators included "sandpapering" on tree trunks near the Maple River and multiple farm vehicles mangled or airborne, contributing to three fatalities and widespread rural devastation including destroyed farms and infrastructure. This upgrade addressed the , attributed to stricter post-2007 survey protocols requiring more rigorous documentation of extreme damage indicators, which had reduced EF5 confirmations despite potential occurrences.

Comparisons and Applications

Differences from the Original Fujita Scale

The Enhanced Fujita (EF) scale, implemented by the National Weather Service on February 1, 2007, introduced several methodological refinements compared to the original Fujita (F) scale developed in 1971. A primary difference lies in the estimation of wind speeds: the original F scale was based on the fastest one-mile wind speed, while the EF scale uses 3-second gust speeds, resulting in overall wind speed estimates that are approximately 23% lower for equivalent damage levels. This adjustment better aligns the scale with modern engineering standards and anemometer measurements, reducing overestimation of tornado intensities. The EF scale expands the framework for damage assessment by incorporating 28 specific damage indicators (DIs), such as one- or two-family residences, small professional buildings, and utility poles, compared to the original F scale's roughly 12 less formalized indicators focused on general structure types like frame houses and barns. Additionally, each DI in the EF scale includes up to 8 degrees of damage (DOD) levels, providing finer than the original's 3 DOD levels per category, which allowed for more precise correlation between observed destruction and inferred wind speeds. These enhancements enable surveyors to account for variations in quality, age, and materials, leading to more accurate and consistent ratings. The shift to the EF scale has notably impacted historical and ongoing tornado ratings, with many events previously classified as F3 being downgraded to EF2 due to the stricter criteria and reduced wind speed thresholds. For instance, the 1999 Bridge Creek–Moore tornado, originally rated F5 with an estimated 301 mph wind, was re-evaluated under EF criteria as EF5 but with a lower expected wind speed range exceeding 200 mph, reflecting the scale's conservative approach to damage-wind correlations. During the transition period, comparisons between F and EF ratings were made for some tornadoes, revealing a trend toward fewer high-end classifications overall. This conservatism contributed to a prolonged "EF5 drought" from the 2013 Moore tornado until the June 20, 2025, Enderlin, North Dakota, tornado was upgraded to EF5 on October 6, 2025, marking the first such rating in over 12 years.
CategoryOriginal F Scale (Fastest-Mile Winds, mph)EF Scale (3-Second Gusts, mph)
F0/EF040–7265–85
F1/EF173–11286–110
F2/EF2113–157111–135
F3/EF3158–206136–165
F4/EF4207–260166–200
F5/EF5Over 260Over 200
These revised wind speed ranges exemplify how the EF scale prioritizes damage-based precision over the original's broader approximations, ultimately improving the reliability of assessments.

Use in Other Countries

adopted the Enhanced Fujita (EF) scale on April 1, 2013, through Environment Canada, replacing the original with adjustments for metric measurements (kilometers per hour) and local building types such as timber-frame houses common in the region. This implementation allows for more precise damage assessments tailored to Canadian infrastructure, including rural structures and forested areas. For instance, during the September 21, 2018, outbreak in and , an EF2 struck the (Nepean) area, causing significant damage to homes and power lines with estimated winds up to 220 km/h. In , the EF scale has influenced the development of adapted versions, such as the International Fujita (IF) scale introduced by the European Severe Storms Laboratory in 2023, which provides a framework compatible with EF methodologies but accounts for European construction standards like brick and stone buildings. Countries including and the apply EF-like scales for rating, often through national weather services or research bodies, emphasizing damage to and lighter structures prevalent in the region. These adaptations facilitate consistent intensity estimates across diverse landscapes, from Scandinavian forests to Dutch polders. Adaptations of the EF scale extend to Asia and other regions, with Japan implementing the Japanese Enhanced Fujita (JEF) scale in April 2016 via the to better evaluate damage to traditional wooden and concrete structures. In Australia, the and Geoscience Australia reference the EF scale for assessing tornadoes. They incorporate local indicators, such as eucalyptus trees and rural sheds, as seen in the 2019 Bendigo EF2 event with winds exceeding 200 km/h. International versions often include additional damage indicators (DIs) for non-Western construction, such as concrete block homes in developing regions. These adaptations address cultural and material differences. By 2025, approximately 10 countries have adopted or adapted the EF scale, including post-2020 implementations in parts of . These efforts involve collaboration through organizations like the (WMO), which references the EF scale in its for global tornado intensity estimation. The EF scale's international adoption enhances global tornado research by standardizing damage-based ratings, enabling cross-border databases such as the European Severe Weather Database, which integrates IF-scale data for comparative analysis and climatological studies. This facilitates better understanding of tornado patterns beyond North America, supporting disaster preparedness in regions with varying building practices and wind metrics.

Limitations and Criticisms

See also:

Challenges in Rating

One major challenge in applying the Enhanced Fujita (EF) scale stems from subjectivity in damage assessments, which can vary significantly based on the experience of surveyors conducting the evaluations. The EF scale relies on interpretation of damage indicators (DIs) and degrees of damage (DODs), but differences in surveyor judgment, particularly regarding construction quality and material variability, often lead to inconsistencies in estimates and final ratings. For instance, adjustments for poor construction quality in residential structures can result in rating variations of up to one EF level between experienced and less experienced teams, as the scale's guidelines allow for qualitative adjustments that are not fully standardized. Notable examples include the 2013 El Reno, Oklahoma, tornado, officially rated EF3 despite mobile radar measurements indicating winds exceeding 300 mph, primarily due to the lack of substantial damage indicators in sparsely populated rural areas. Another case is the 2023 Rolling Fork, Mississippi, tornado, rated EF4 but considered an EF5 candidate by some analyses based on damage to certain structures, highlighting interpretive differences in assessing degrees of damage. Environmental factors further complicate EF scale ratings by limiting access to reliable damage indicators in certain terrains. In densely forested areas or regions with heavy urban clutter, such as debris-filled streets or obstructed views from high-rises, thorough ground surveys become difficult, often resulting in incomplete data and potential underestimation of tornado intensity. Rural landscapes, in particular, pose challenges due to sparse traditional DIs like buildings, making it harder to apply the scale's 28 categories effectively compared to urban settings with abundant structures. Additionally, weak tornadoes (EF0-EF1) are frequently underrated or even unrated because of poor documentation and minimal visible damage, exacerbating underreporting in areas without eyewitness accounts or photographic evidence. Biases in the EF scale application also arise from its over-reliance on residential and commercial structures as primary DIs, which disadvantages assessments in non-built environments. This structural focus can lead to rural-urban disparities, where tornadoes in rural areas with fewer well-constructed buildings receive lower ratings due to limited evidence of high winds, even if vegetation or agricultural damage suggests otherwise. In contrast, urban tornadoes benefit from diverse DIs like power poles and vehicles, potentially inflating ratings, while rural events suffer from a scarcity of comparable indicators, contributing to broader inaccuracies in intensity estimation. Recent challenges highlight ongoing issues with the scale's stringent criteria, exemplified by the "EF5 drought" from 2013 to 2025, during which no tornadoes were rated EF5 despite numerous violent events. This prolonged absence is largely attributed to the EF scale's stricter wind speed thresholds and adjustments for improved building codes, which require "incredible" damage to well-constructed structures for an EF5 rating, often downgrading what might have been F5 under the original scale. The 2025 Enderlin, North Dakota, tornado illustrates how integrated approaches can address these hurdles; initially rated EF3, it was upgraded to EF5 following detailed re-analysis of extreme damage indicators, supported by radar-derived wind estimates exceeding 200 mph, demonstrating the value of combining radar data with traditional surveys to refine ratings. Studies on underscore the scale's variability, revealing inconsistencies in damage assessments that can affect overall rating accuracy, particularly for borderline cases between EF levels. To mitigate subjectivity, technologies like drones and AI have emerged post-2020 as tools for , enabling high-resolution imagery of hard-to-reach areas and automated analysis of damage patterns to better align with EF scale criteria. For example, drone surveys provide hyperspatial views that enhance DI identification in cluttered or forested zones, reducing human in estimation.

Future Improvements

Ongoing research by the and the emphasizes integrating techniques to automate the identification of damage indicators (DIs) in tornado assessments, aiming to enhance the accuracy and speed of EF scale ratings. For instance, models have been developed to analyze and detect structural damage, such as fallen trees or building deformations, which can inform EF ratings by estimating s from visual cues without relying solely on manual surveys. These initiatives, including NOAA-supported projects like the Low-Level INsitu Tornado Intensity Forecast (LIFT) experiment, seek to collect ground-level data in the lowest 20 meters of tornadoes to refine correlations with damage, addressing gaps in current post-event evaluations. International collaborations are advancing toward a unified global tornado rating framework through the International Fujita (IF) Scale, developed by the European Severe Storms Laboratory (ESSL) and partners since 2023, which adapts the EF scale's principles for worldwide application. This scale incorporates a broader catalog of DIs tailored to diverse building practices and environments, facilitating consistent intensity assessments across countries and supporting cross-border research on . Complementing this, a 2025 global digitized tornado database, compiled by international researchers, standardizes occurrence records to improve long-term studies and scale validations, potentially informing future EF revisions. Long-term goals include real-time EF rating capabilities using radar data, sensors, and predictive algorithms to supplement traditional damage-based assessments, particularly as climate-driven shifts in tornado patterns may increase event intensity. Studies suggest minor adjustments to EF scale boundaries, such as the EF4/EF5 threshold, could better align historical and modern ratings amid observed "droughts" in high-end tornado classifications. These efforts prioritize enhancing public safety and scientific understanding without altering the core EF structure from EF0 to EF5.

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