EF-scale

EF-scale
Name	EF-scale
Caption	Enhanced Fujita scale chart
Area	International (primarily United States)
Introduced	2007
Predecessor	Fujita scale
Developer	United States National Weather Service; Ted Fujita (original Fujita)

EF-scale

The EF-scale is a standardized damage-based rating system used to estimate wind speeds and categorize the intensity of tornadoes, providing a basis for post-event analysis by agencies such as the National Weather Service and research institutions including the National Severe Storms Laboratory and the Storm Prediction Center. It replaced an earlier classification developed by Ted Fujita and colleagues, aligning damage indicators with engineering studies from universities such as Texas Tech University and Iowa State University. The scale is widely referenced in incident reports from municipal authorities in cities like Oklahoma City, Joplin, Missouri, and Tuscaloosa, Alabama and is used in climatological studies by organizations such as the National Oceanic and Atmospheric Administration.

Overview

The EF-scale categorizes tornado intensity using damage indicators derived from observed effects on buildings and infrastructure, linking those indicators to estimated three-second gust wind speeds for ratings from EF0 through EF5. Operational agencies including the National Weather Service, the Federal Emergency Management Agency, and state emergency management offices apply the scale during damage surveys following events like the 2011 Super Outbreak and the May 2013 tornado outbreak sequence. Academic analyses in journals from institutions such as Purdue University and University of Oklahoma use EF-scale data to study tornado climatology, risk assessment, and building performance.

History and development

The original Fujita scale, introduced by Ted Fujita at the University of Chicago in 1971, categorized tornadoes from F0 to F5 based on damage photos and anecdotal evidence from events such as the Tri-State Tornado and the 1974 Super Outbreak. Concerns about wind speed estimations led agencies including the National Weather Service and the Wind Science and Engineering Research Center at Texas Tech University to collaborate on revisions. The Enhanced Fujita effort incorporated structural engineering research from Iowa State University, field surveys from NWS Norman, Oklahoma offices, and input from organizations like the American Society of Civil Engineers before formal adoption by the National Weather Service in 2007.

Scale description and ratings

The EF-scale comprises six primary categories: EF0, EF1, EF2, EF3, EF4, and EF5. Each rating corresponds to a range of estimated three-second gust wind speeds and damage descriptions tied to specific damage indicators such as one- or two-family residences, manufactured homes, and high-rise buildings. The scale’s numerical thresholds were informed by engineering analyses from FEMA studies and academic work at University of Illinois Urbana–Champaign and Mississippi State University. The EF5 category denotes incredible damage and is reserved for events that cause total destruction of well-constructed structures, often referenced in reports about the Moore, Oklahoma tornado (2013), the Joplin tornado (2011), and the El Reno tornado (2013).

Methodology and damage assessment

Damage surveys conducted by National Weather Service teams, state emergency management agencies, and university researchers utilize over 25 damage indicators and degrees of damage calibrated to construction types and building practices from regions such as Midwest United States and Southeastern United States. Surveyors assess damage to targets like schools, hospitals, and commercial structures, cross-referencing findings with engineering guidance from ASCE manuals and case studies from Texas A&M University. Photogrammetry, mobile Doppler radar data from projects like VORTEX2, and forensic engineering reports supplement ground surveys. Results are compiled in situational reports used by agencies including NOAA and state departments of transportation.

Applications and limitations

Agencies such as the National Weather Service and FEMA use EF-scale ratings for emergency response planning, insurance claim assessment by companies such as State Farm and Allstate, and scholarly research in meteorology departments at Penn State University and University of Alabama. Limitations include the scale’s reliance on available damage indicators—rural events with few structures may yield lower ratings despite high winds—and regional variations in construction that affect damage outcomes, noted in studies from University of Missouri and Auburn University. The scale does not directly measure wind speed; rather, it infers wind estimates from observed damage, a constraint highlighted in analyses from National Academy of Sciences panels and hurricane-tornado comparative studies involving NOAA and NASA.

Comparison with other scales

The EF-scale evolved from the original Fujita scale; both use damage to infer wind speeds but differ in calibration and engineering support. Internationally, the EF-scale is compared to the TORRO scale used in the United Kingdom and parts of Europe and to intensity metrics applied in Canada by Environment and Climate Change Canada. Researchers at Monash University and University of Helsinki have explored correlations between EF ratings and other intensity indices used in tornado climatology and risk modeling, such as those employed in the European Severe Storms Laboratory.

Notable tornadoes rated on the EF-scale

Significant EF-scale events include the Joplin tornado (2011) (EF5), the Moore tornado (2013) (EF5), the El Reno tornado (2013) (rated EF3 by survey although studied extensively with mobile Doppler data), and multiple EF4/EF5 tornadoes associated with the 2011 Super Outbreak. Other notable ratings appear in the aftermath of the Greensburg tornado (2007), Hattiesburg tornado (2013), and the Tuscaloosa–Birmingham tornado (2011), each cited in National Weather Service storm reports and peer-reviewed literature.

Category:Weather scales