Southeasterners Perceive Tornado Risk Dangerously Different Than They Should, Especially at Night

While a major winter storm last month was plastering the United States from Texas and New Mexico to New England with heavy snow and ice, volatile conditions in the Southeast (SE) spawned damaging and deadly tornadoes. One of these overnight Monday, February 16, tragically took the lives of 3 people and injured 10 in coastal North Carolina. Such nocturnal tornadoes are common in the Southeastern U.S.—a unique trait—and represent an extreme danger to sleeping residents.


Compounding this problem, new research in the AMS journal Weather, Climate, and Society suggests there may be a deadly disconnect between tornado perception and reality in the region right when residents instead need an acute assessment of their tornado potential.
The article “Do We Know Our Own Tornado Season? A Psychological Investigation of Perceived Tornado Likelihood in the Southeast United States,” by Stephen Broomell of Carnegie Mellon University, with  colleagues from Stanford and NCAR, notes the tragic results of the regional misperception:

The recurring risks posed by tornadoes in the SE United States are exemplified by the significant loss of life associated with recent tornado outbreaks in the SE, including the 2008 Super Tuesday outbreak that killed over 50 people and the devastating 27 April 2011 outbreak that killed over 300 people in a single day.

Their survey of residents in seven states, from Louisiana and Arkansas to Georgia and Kentucky, representing the Southeastern region, finds that the residents perceive their tornado likelihood differently than meteorologists and experts familiar with Southeastern tornado risk. This puts them at great risk because residents’ experiences don’t match what actually happens where they live.

Broomell and his fellow researchers contend that Southeast residents may be misusing knowledge of Great Plains tornado events, ubiquitous in tornado chasing reality shows and social media videos, when determining their own risk. A fatal flaw since tornado behavior is different between the two regions.
WCAS SE tornado season survey2For starters, unlike in infamous “Tornado Alley” states of Texas and Oklahoma north through Nebraska and Iowa into South Dakota, the Southeast lacks a single, “traditional” tornado season, with tornadoes “spread out across different seasons,” Broomell along with his coauthors report, including wintertime. The Southeast also endures more tornadoes overnight, as happened last week in North Carolina. And they spawn from multiple types of storm systems in the Southeast, more so than in the Great Plains. This makes knowledge about residents’ regional tornado likelihood especially critical in Southeastern states.

Another recent study published in the Bulletin of the American Meteorological Society, “In the Dark: Public Perceptions of and National Weather Service Forecaster Considerations for Nocturnal Tornadoes in Tennessee,” by Kelsey Ellis (University of Tennessee, Knoxville), et al., surveyed residents of Tennessee and came away with similar findings about tornado timing: about half of Tennessee’s tornadoes occur at night, and yet less than half of those surveyed thought they would be able to receive nighttime tornado warnings.

Local forecasters and broadcast meteorologists as well as emergency managers are tuned into the mismatch. In the BAMS study, NWS forecasters said they fear for the public’s safety, particularly with nighttime tornadoes, because they “know how dangerous nocturnal events are”—fatalities “are a given,” some said.

Ellis and her colleagues recommended developing a single, consistent communication they term “One Message” to focus on getting out word about the most deadly aspect of the tornado threat. Forecasters, broadcasters, and emergency managers through regular and social media would then be consistent in their messaging to residents, the researchers state, decreasing confusion. For example:

Nighttime tornadoes expected. Sleep with your phone ON tonight!

With severe weather season ready to pop as spring-like warmth quickly overwhelms winter’s icy grip in the next couple of weeks, the nation’s tornado risk will blossom across the South and Southeast. And nocturnal tornado threats will only increase, particularly in the Southeast, as February turns into March, and then April—a historically deadly month.
For residents in places more prone to nighttime tornadoes, Ellis et al. say the ways to stay safe are clear:

Have multiple ways to get tornado warnings, do not rely on outdoor sirens, sleep with your phone on and charged during severe weather, and do not stay in particularly vulnerable locations such as mobile homes or vehicles.

“Sleep with your phone on!”: Messaging for Nighttime Tornadoes

With Hurricane Delta poised to strike Louisiana today, the risk of embedded tornadoes will increase as rainbands spiral ashore, along with the primary threats of storm surge and damaging winds. Delta is forecast to plow well inland Friday night into the weekend, continuing a low risk for tornadoes, some of which could occur at night in Alabama, Mississippi and into southern Tennessee. The threat is more than a bit worrisome as new research in BAMS finds through phone surveys and followup interviews in Tennessee that people are woefully unprepared for nocturnal tornadoes.

In their article,” Kelsey Ellis and colleagues found a host of poor practices by residents when it comes to tornadoes at night. The authors recommend forecasters narrow their messaging about nocturnal tornadoes in the Southeast to a single important message to limit confusion.

Almost half of Tennessee’s tornadoes occur at night, as in other Southeast states with large numbers of nocturnal tornadoes, and are two-and-a-half times as deadly as daytime tornadoes. This creates detection, warning, and public response challenges. Yet, respondents in the western part of the state overestimated tornado occurrence at night while those in the east substantially underestimated the number.

Additionally, nearly half of participants in the survey say they rely on sirens to receive tornado warnings. This is despite the fact that sirens are not designed to warn people inside nor be loud enough to wake anyone up. Instead, Wireless Emergency Alerts (WEAs) “should be a constant,” the authors say. Also, people mentioned they rely on TV and social media for receiving warnings even though generally neither will wake you up.

The authors felt it was “dangerous” that even the more tech savvy and tornado aware respondents answered they were compelled to look outside for evidence of a tornado—even in the dark. Interviewees explained they were “checking for sounds instead of visual cues.”

NWS forecasters were also surveyed about nocturnal tornadoes. The forecasters mentioned the lack of ground truth and fear for public safety among challenges to the nighttime warning service. They noted few spotter or social media reports inform them if “the storm is actually showing the signs on the grounds that radar is indicating aloft.” Forecasters said they felt “fearful, worried, or nervous for the public during nocturnal tornadoes because fatalities ‘are a given.’”

The survey responses moved Ellis et al. to recommend a single-emphasis message be presented to residents to combat the nighttime tornado problem:

One strategy that may improve public safety during a nocturnal tornado event, and which addresses the forecaster challenge of communication prior to and during an event, is to develop “One Message”—a consistent message that EMs and the media use throughout broadcasts, briefings, and social media. Examples of messages could be: “Nighttime tornadoes expected. Sleep with your phone ON tonight!” or “Tornadoes will form quickly! Make plans now where you will take shelter!” or “If you live in a manufactured home, you may not have much time to seek shelter tonight!” One Message may decrease confusion for receivers, making them more likely to make safe decisions. Messages could similarly be used to dispel misconceptions about local geography in ways relevant to the specific listening area, for example: “You are not protected by nearby hills. Seek shelter immediately!”

With Hurricane Delta’s nighttime tornado threat ramping up, the authors suggest people use multiple ways to receive warnings, keeps phones on and charged, don’t rely on tornado sirens, and if possible relocate ahead of the weather from “particularly vulnerable” situations, such as mobile homes and vehicles.

"Sleep with your phone on!": Messaging for Nighttime Tornadoes

With Hurricane Delta poised to strike Louisiana today, the risk of embedded tornadoes will increase as rainbands spiral ashore, along with the primary threats of storm surge and damaging winds. Delta is forecast to plow well inland Friday night into the weekend, continuing a low risk for tornadoes, some of which could occur at night in Alabama, Mississippi and into southern Tennessee. The threat is more than a bit worrisome as new research in BAMS finds through phone surveys and followup interviews in Tennessee that people are woefully unprepared for nocturnal tornadoes.
In their article,” Kelsey Ellis and colleagues found a host of poor practices by residents when it comes to tornadoes at night. The authors recommend forecasters narrow their messaging about nocturnal tornadoes in the Southeast to a single important message to limit confusion.
Almost half of Tennessee’s tornadoes occur at night, as in other Southeast states with large numbers of nocturnal tornadoes, and are two-and-a-half times as deadly as daytime tornadoes. This creates detection, warning, and public response challenges. Yet, respondents in the western part of the state overestimated tornado occurrence at night while those in the east substantially underestimated the number.
Additionally, nearly half of participants in the survey say they rely on sirens to receive tornado warnings. This is despite the fact that sirens are not designed to warn people inside nor be loud enough to wake anyone up. Instead, Wireless Emergency Alerts (WEAs) “should be a constant,” the authors say. Also, people mentioned they rely on TV and social media for receiving warnings even though generally neither will wake you up.
The authors felt it was “dangerous” that even the more tech savvy and tornado aware respondents answered they were compelled to look outside for evidence of a tornado—even in the dark. Interviewees explained they were “checking for sounds instead of visual cues.”
NWS forecasters were also surveyed about nocturnal tornadoes. The forecasters mentioned the lack of ground truth and fear for public safety among challenges to the nighttime warning service. They noted few spotter or social media reports inform them if “the storm is actually showing the signs on the grounds that radar is indicating aloft.” Forecasters said they felt “fearful, worried, or nervous for the public during nocturnal tornadoes because fatalities ‘are a given.’”
The survey responses moved Ellis et al. to recommend a single-emphasis message be presented to residents to combat the nighttime tornado problem:

One strategy that may improve public safety during a nocturnal tornado event, and which addresses the forecaster challenge of communication prior to and during an event, is to develop “One Message”—a consistent message that EMs and the media use throughout broadcasts, briefings, and social media. Examples of messages could be: “Nighttime tornadoes expected. Sleep with your phone ON tonight!” or “Tornadoes will form quickly! Make plans now where you will take shelter!” or “If you live in a manufactured home, you may not have much time to seek shelter tonight!” One Message may decrease confusion for receivers, making them more likely to make safe decisions. Messages could similarly be used to dispel misconceptions about local geography in ways relevant to the specific listening area, for example: “You are not protected by nearby hills. Seek shelter immediately!”

With Hurricane Delta’s nighttime tornado threat ramping up, the authors suggest people use multiple ways to receive warnings, keeps phones on and charged, don’t rely on tornado sirens, and if possible relocate ahead of the weather from “particularly vulnerable” situations, such as mobile homes and vehicles.

Website Tracks Public Understanding of Tornadoes

Imagine you live in a part of the country where few people have experienced tornadoes. It would make sense that your neighbors wouldn’t know the difference between a tornado watch or warning, or know how to seek safety.

A new, openly available online tool shows exactly that, by combining societal databases with survey results about people’s understanding of weather information. But there are some surprising wrinkles in the data. For example, the database drills down to county-level information and finds “noteworthy differences” within regions of similar tornado climatology.

How is it that Norman, Oklahoma, residents score higher in what people think they know of severe weather information than those in Fort Worth, Texas? And why is there a similar gap between what people actually do know, as tested in Peachtree City, Georgia, versus Birmingham, Alabama?

“Differences like this create important opportunities for research and learning within the weather enterprise,” say Joseph T. Ripberger and colleagues, who describe the weather demographics tool in a recently published Bulletin of the American Meteorological Society article. “The online tool—the Severe Weather and Society Dashboard (WxDash)—is meant to provide this opportunity.”

For example, in one key set of metrics, the WxDash website looks at survey data on how well people receive and pay attention to tornado warnings (reception), how well they understand that information (both “subjective” comprehension—what people think they know—and “objective” comprehension—what they actually know), and response to tornado warnings.

From the BAMS article, a figure showing knowledge and response to average person percentile (APP) estimates of tornado warning reception, subjective comprehension, objective comprehension, and response by county warning area (CWA). The inset plots indicate the frequency distribution of APP estimates across CWAs. These estimates compare the average percentile of all adults who live in a CWA to the distribution of all adults across the country. For example, an APP estimate of 62 indicates that, on average, adults in that CWA score higher than 62% of adults nationally. The range of APP scores is wide. CWAs range from 38 to 61 on the reception scale, 32 to 69 on the subjective comprehension scale, and 37 to 60 on the objective comprehension scale. Response scores vary less. Not surprisingly, all categories broadly reflect the higher frequency of tornadoes in middle and southeastern CWAs.
From the BAMS article, a figure showing knowledge and response to average person percentile (APP) estimates of tornado warning reception, subjective comprehension, objective comprehension, and response by county warning area (CWA). The inset plots indicate the frequency distribution of APP estimates across CWAs. These estimates compare the average percentile of all adults who live in a CWA to the distribution of all adults across the country. For example, an APP estimate of 62 indicates that, on average, adults in that CWA score higher than 62% of adults nationally. The range of APP scores is wide. CWAs range from 38 to 61 on the reception scale, 32 to 69 on the subjective comprehension scale, and 37 to 60 on the objective comprehension scale. Response scores vary less. Not surprisingly, all categories broadly reflect the higher frequency of tornadoes in middle and southeastern CWAs.

 

WxDash combines U.S. Census data with an annual Severe Weather and Society Survey (Wx Survey) by the University of Oklahoma Center for Risk and Crisis Management. The database then “downscales” the broader scale information to the local level, in a demographic equivalent to the way large scale climate models downscale to useful information on regional scales.

The site also provides information on public trust in weather information sources, perceptions about the efficacy of protective action, vulnerability to beliefs about a variety of tornado myths, and other weather-related factors that can then be studied in light of regional and demographic factors.

Some of the key findings seen in the database:

  • Men and women demonstrate roughly comparable levels of reception, objective comprehension, and response, but men have more confidence in subjective warning comprehension than women.
  • Tornado climatology has a relatively strong effect on tornado warning reception and comprehension, but little effect on warning response.
  • The findings suggest that geography, and the community differences that overlap with geographic boundaries, likely exert more direct influence on warning reception and comprehension than on response.

Even the relatively expected relation of severe weather climatology to severe weather understanding is problematic, Ripberger and colleagues write.

Tornadoes are possible almost everywhere in the US and people who live on the coasts can move—both temporarily and permanently— throughout the country. These factors prompt some concern about the low levels of reception and comprehension in some communities, especially those in the west.

In addition to interacting with these data, you can download one of the calculated databases for community-scale information, the raw survey data, and the code necessary to reproduce the calculations.

The idea is social scientists can dig in and figure out why what we know about weather isn’t nearly as closely correlated with what we experience as we might think. The hope is an improvement in public education and risk communication strategies related to severe weather.

10-m Resolution Quarter-Trillion Gridpoint Tornadic Supercell Simulation Mesmerizes

An exceptionally high resolution simulation of a supercell thunderstorm fascinated conferees Tuesday at the AMS 100th Annual Meeting in Boston. Leigh Orf of the University of Wyoming presdented imagery and animations of the simulation that ran on the Blue Waters Supercomputer. With a 10 m grid spanning 11,200 X 11,200 X 2,000 (251 billion) grid volumes, the 270 TB subdomain contains the entire life cycle of the tornado, including 10 minutes prior to tornado formation.

Image created with VAPOR3 of a 10-m supercell simulation. (a) Volume rendered cyclonic vertical vorticiy, highlighting the 3D structure of the tornado shortly after formation.
Image created with VAPOR3 of a 10-m supercell simulation. (a) Volume rendered cyclonic vertical vorticity, highlighting the 3D structure of the tornado shortly after formation. The 2D surface field traces the maximum surface cyclonic vertical vorticity, providing a representation of the tornado’s path. The view is following the tornado’s path. (b) As in (a), but later in the simulation when the tornado exhibits a multiple vortex structure. (c) Volume rendered cloud mixing ratio, with parameters chosen to present a quasi-photorealistic view of the cloud field. The 2D surface field traces the minimum pressure found in the tornado’s path. (d)  As in (a) and (b), but a different, wider view and utilizing different opacity and color map choices. The vortex to the left, which merges with the tornado later in the simulation, is weaker than the nascent tornado as evidenced by the vortex’s more transparent and darker visual presentation and path.

 

Tornado Researchers Gather to Improve Wind Speed Estimation

The Wind Speed Estimation (WSE) standards committee–jointly supported by AMS and the American Society of Civil Engineers–is holding its 9th meeting this week in conjunction with an NSF-funded Tornado Hazard Wind Assessment and ReducTion Symposium (THWARTS) at the University of Illinois in Champaign-Urbana.
The WSE committee began in 2014 to develop standards for an improved process to estimate extreme storm winds. Currently, NWS and private post-storm damage surveys use the EF-Scale and treefall pattern analysis, real-time radar and in situ observations, remote sensing, and forensic investigations. The WSE committee includes a data archival team as well as an international working group to broaden the scope of the standard. (Click here for more information about the committee.)
WSE
This is the second joint meeting of WSE/THWARTS and will focus on sharing the latest findings on the multidisciplinary aspects of severe local storms, including the fields of meteorology, wind science and engineering, structural engineering, social science, and policy. A flyer about the symposium with basic information is available online.
Keynote speaker for THWARTS will be Erik Rasmussen. He was the field coordinator of the first of the VORTEX projects in 1994-1995 and a lead principal investigator for VORTEX2 from 2009-2010 and VORTEX-SE from 2016-2017. He currently consults with NOAA’s National Severe Storms Laboratory and the Cooperative Institute for Meteorological Satellite Studies.
The WSE meeting begins after the final session of THWARTS. The meeting is the first step toward a request for public comment on WSE, likely next year.

Making Sure No Tornado Damage Is Too Small

Planetary, synoptic, meso-alpha, meso-beta, local, and more—there are atmospheric scales aplenty discussed at AMS meetings. Enter microtopography, a once-rare word increasingly appearing in the mix in research (for example, here and here).
The word is also coming up as researchers are getting new tools to examine the interaction of tornadoes with their immediate surroundings. Microtopography looks like a potential factor in tornadic damage and in the tornadoes themselves, according to an AMS Annual Meeting presentation by Melissa Wagner (Arizona State Univ.) and Robert Doe (Univ. of Liverpool), who are working on this research with Aaron Johnson (National Weather Service) and Randy Cerveny (Arizona State Univ). Their findings relate tornado damage imagery to small changes in local topography thanks to the use of unmanned aerial systems (UASs).
Microtopographic interactions of tornadic winds were captured in their UAS imagery. Here’s the 5-meter resolution RapidEye satellite imaging of a 30 April 2017 Canton, Texas, tornado path (panel a) versus higher-resolution UAS imaging:
UAS damage figure 1
 
The UAS surveys show that tornadic winds interact with sunken gullies, which appear as unscarred, green breaks (circled in red) in the track of browned damaged vegetation:
UAS damage fig. 3
Erosion and scour are limited within the depressed surfaces of the gullies compared to either side. In another section of the track, track width increases with an elevation gain of approximately 74 feet, as shown in a digital elevation model and 2.5 cm resolution UAS imagery:
UAS damage 3+
The advent of unmanned aerial vehicles (UAVs) has opened new windows on tornado damage tracks. Decades ago, damage surveys took a big leap forward with airplane-based photography that provided a perspective difficult to achieve on the ground. Satellites also can provide a rapid overview but in relatively low resolution. UASs fly at 400 feet—and are still limited to line-of-sight control and the logistics of coordinating with local emergency and relief efforts, regulatory and legal limitations, not to mention still-improving battery technology.
However, UASs provide a stable, reliable aerial platform that benefits from high-resolution imaging and can discern features on the order of centimeters across. Wagner and colleagues were using three vehicles with a combined multispectral imaging capability that is especially useful in detecting changes in the health of vegetation. As a result their methods are being tested primarily in rural, often inaccessible areas of damage.
UAS technologies thus can capture evidence of multi-vortex tornadoes in undeveloped or otherwise remote, vegetated land. The image below shows a swath with enhanced surface scour over two hills (marked X). The arrow on the right identifies speckled white surface erosion, part of the main tornado wedge. Such imagery explains why, among other research purposes, Wagner and Doe are developing the use of UASs in defining tracks and refining intensity-scale estimates.
UAS damage Figure 4

A Tale of Two Studies: Varied Perspectives at the AMS Meeting

by Maggie Christopher, Valparaiso University
On Sunday students presented nearly 200 posters of their research in grad school and summer internships. With so many topics covered, the session covered a variety of perspectives—often multiple perspectives on similar questions.
For example, two students from different universities did individual studies of the socioeconomic factors in fatalities due to tornadoes. But while Shadya Sanders from Howard University compared two case studies, Omar Gates, from the University of Michigan, set one tornado case in a climatological perspective.
Sanders compared the Joplin, Missouri, and Tuscaloosa, Alabama, tornadoes in 2011. Sanders looked at the differences in death rates for race, age, gender, and housing structures in each storm. She found, for example, a high rate of death amongst women, which she said is unusual compared to other data she looked at. Women generally will take the suggested protective action when warnings are issued.
Sanders also noticed that in Tuscaloosa people aged 21-30 died at a higher rate, probably because the University of Alabama is located in the city of Tuscaloosa. By contrast, in Joplin, more retail business were located in the path of the storm, rather than houses.
Similarly, Gates studied the effect of tornado outbreaks as climate changes. He hoped to show the risk of tornadoes striking cities. He focused his research on Oklahoma, and specifically the May 3, 1999 tornado in Moore. Gates used reanalysis data with the North American Regional Reanalysis (NARR), and also utilized 2010 Census Data, which included demographic information such as gender, race, age, and housing units.
Using ARCgis, Gates put together risk assessment maps for vorticity, moist static energy, and wind shear. These maps were then put together, along with the actual storm track, to locate the highest risk of tornadoes for that day.
Even with different approaches, Shayda and Gates had similar goals for their work. Shayda held focus groups in both cities to see what kinds of warnings citizens would find most helpful. She wants to insure that warnings get out to everyone, and she hopes to continue her research throughout the rest of the United States. Similarly, Gates hopes that continuing to look at the socioeconomic effects of tornadoes will lead to watches, outlooks, and warnings that are easier for people to decipher, saving lives.
 

New Standard Aims to Improve Tornado, Severe Wind Estimates

By Jim LaDue, NWS Warning Decision Training Branch
For more than four decades, the go-to for rating tornadoes has been the Fujita Scale, and in the last eight years, the Enhanced Fujita Scale, or EF Scale. Soon, scientists and NWS field teams will have a new and powerful benchmark by which to gauge the extreme winds in tornadoes and other severe wind events.
The American Society of Civil Engineers (ASCE) has approved the EF Scale Stakeholder Group’s proposal to develop a new standard for estimating wind speeds in tornadoes. This standard will allow, for the first time, a rigorous process to improve not only the EF-scale but to adopt new methods to assign wind speed ratings to tornadic and other wind events.
The intent is to standardize methods. According to the ASCE blog, “The content of the standard would include improvements to the existing damage-based EF scale to address known problems and limitations.” ASCE went on to state that the data used for estimating wind speeds would be archived.
The EF Scale Stakeholders Group, composed of meteorologists, wind and structural engineers, a plant biologist, and a hydrologist, held a series of meetings over the past year to discuss methods available to provide wind speed estimations.  The consensus among the group is that many methods exist in addition to that used in the EF Scale today.  These include mobile Doppler radar, tree-fall pattern analysis, structural forensics, and in situ measurements.  The group also discussed ways that the EF Scale could be improved through the correction of current damage indicators and by adding new ones. The outcome of these discussions is available online.
The new standard will be housed under the Structural Engineering Institute (SEI) of the ASCE.  Users of the standard include but are not limited to wind, structural, and forensic engineers, meteorologists, climatologists, forest biologists, risk analysts, emergency managers, building and infrastructure designers, and the media.
Interested parties are encouraged to apply to the committee, selecting Membership Category as either a General member with full voting privileges or as an Associate member with optional voting capabilities. Membership in ASCE is not required to serve on an ASCE Standards Committee.
The online application form to join the committee is available at http://www.asce.org/codes-standards/applicationform/.
The new committee will be chaired by Jim LaDue and cochaired by Marc Levitan of the National Institute of Standards and Technology. For more information or questions about joining the committee, please contact us at james . g . ladue @ noaa . gov and marc . levitan @ nist . gov.

Reassessing the Enhanced Fujita Tornado Scale

It’s been more than 40 years since Ted Fujita introduced his renowned Tornado Damage Scale – the Fujita Scale. And nearly a decade has passed since top tornado scientists first collaborated with structural engineers to create the Enhanced Fujita (EF) Scale for rating tornado winds more accurately based on advances in our understanding of the variety of damage they inflict. Now, an effort is underway to tweak the EF Scale further – and the National Weather Service is looking for input from AMS meeting attendees this week.
The effort stems from the observations and analysis of recent violent tornado events: the massive tornado outbreak across the South in April 2011; the violent (EF5) Joplin, Missouri tornado of May 2011; and the Newcastle-Moore, Oklahoma EF5 tornado of May 2013. Survey teams were able to use more than two dozen “damage indicators,” such as wood-frame homes, strip malls, and schools—each further categorized by multiple “degrees of damage”—to gauge tornadic winds. But questions and even discrepancies arose among the survey teams as they scoured the wreckage of entire neighborhoods.
Oral and poster presentations throughout this week at the AMS Annual Meeting in Atlanta share information about the damage surveys, findings from reports such as the National Institute of Standards and Technology (NIST) technical investigation of the Joplin tornado and FEMA’s Mitigation Assessment Team Report on the Spring 2011 tornadoes, as well as thoughts for improving the EF-scale:

All of these represent on-going thinking about the EF Scale and how to refine it.
If you’d like to get involved, NWS is hosting an open discussion of the EF Scale to acquire feedback on its strengths and deficiencies. Space is limited so sign up today.