Tornado Outbreak Research Articles

A Hotter Earth Means Stronger Tornadoes

Although their frequency may decrease, models suggest anthropogenic climate change will increase the intensity of tornado outbreaks.

Prediction of tornado days in the United States with deep convolutional neural networks

Tornado outbreaks in the United States have caused large numbers of human and economic losses. The analysis of gridded climate data to find spatial patterns of meteorological variables that produce tornadoes is often a time consuming and manual process requiring visual inspection. Therefore, the ability to train convolutional neural networks (CNNs) to recognize patterns in climate data that produce tornado outbreaks would be a huge benefit to climatologists. In this paper, three CNNs of increasing complexity, including LeNet-5, VGG-16, and Resnet-50 were trained to predict days with tornado outbreaks of varying size based on gridded values of convective available potential energy (CAPE), convective inhibition (CIN), storm relative helicity (HLCY), and geopotential height. All three models showed promising results in predicting large tornado outbreaks with greater than 20 tornadoes with VGG-16 using the variable CAPE having a slightly better performance, highlighting the importance of CAPE in the analysis of tornado environments.

Would “Tornado-Preventing” Walls Work?

Simulations were performed using the Weather Research and Forecasting model in order to evaluate a proposal that called for the construction of three east–west “great walls” in the American Midwest to eliminate the major threat of tornadoes in Tornado Alley. The results of three simulations using the 31 May 2013 tornado outbreak are presented—one with natural terrain, one with 300-m tall walls as proposed, and another with walls much taller than proposed (2500 m). Through comparisons of temperature, moisture, instability, and supercell and tornado composite forecasting parameters, the “tornado-preventing” walls, as proposed, are shown to have very little impact on the atmosphere. When the height of the walls is greatly increased, the location of convective storms shifts eastward, instead of being eliminated. The short-term impacts of the taller walls imply possible desertification and areas with increased probability of non-supercellular tornadoes near the edges of the walls.

Russian Tornado Outbreak of 9 June 1984

The tornado outbreak of 9 June 1984 is among the most important tornado events in Russia’s history because it was associated with substantial loss of life (400 deaths), and contained one of two F4 tornadoes on record for that country. Also, a 1-kg hailstone was observed, comparable to the heaviest on world record. The synoptic and mesoscale environments are examined and previous studies of this case are revisited to confirm or dispute findings. One of the major findings in dispute is the source of the low-level moist air mass, which is shown to be the Black Sea. Due to the paucity of previous studies, the authors also surveyed the typical sources of low-level moisture for tornado events in the western part of the former Soviet Union.
 Despite the limited information available about the tornadoes for this case (at least relative to significant tornado events in the United States), the authors present details from eyewitness accounts, previous studies, and modernized updates from the European Severe Weather Database (ESWD). Satellite data were studied in order to augment this limited information and to refine event locations and times. A map of storm tracks is presented, along with reasons why it differs in some instances from previous studies.

In Situ Observations of the 21 April 2007 Tulia, Texas Tornado

A localized tornado outbreak occurred across the Texas Panhandle during the afternoon and evening hours of 21 April 2007. One supercell thunderstorm produced an EF2 tornado in the town of Tulia, TX. A mobile mesonet vehicle was struck by the tornado while fortuitously collecting in situ data near the center of the vortex. The instrumentation sufficiently resolved the wind and pressure characteristics, at approximately 2.9 m and 2.6 m respectively above ground level, of the tornado’s micro-α scale environment. A maximum wind of 50.4 m s -1 and a pressure deficit of 194 hPa were measured, yielding the largest known pressure fall within a tornado. Analysis of the recorded data and instrumentation were conducted; results are presented and discussed.

Multivariate Index for Ranking

In previous work, severe weather outbreaks have been classified either as major tornado outbreaks or as primarily nontornadic outbreaks, but the large majority of such events are of a mixed character. This study proposes a reproducible method for ranking all types of severe weather outbreaks from the period 1960-2006. Numerous nonmeteorological artifacts exist in the severe weather reports archived during this period, and many of the variables used to formulate the multivariate indices had to be detrended to reduce the effect of secular trends. The resulting outbreak rankings indicate that the methodology presented herein is able to distinguish the most significant severe weather outbreaks from intermediate outbreak days and days with a large amount of geographic scatter in the severe reports. The rankings of the most severe outbreaks and those outbreak days with a large degree of spatial scatter exhibit only limited variability when the selection of parameters and their weights are modified, but a relatively high degree of volatility is noted with the intermediate cases. This result suggests there is relatively little difference in the severity of these intermediate events. However, the particular modes of severe weather in these events can be quite different. A k-means cluster analysis of the outbreak days, using a four-dimensional representation of the multivariate indices developed, indicates that outbreak days can be separated into five groups: major tornado, wind-dominated, hail-dominated, multi-modal, and days with considerable spatial scatter of the severe reports.

Case Study in Forensic Meteorology: Investigating the 3 April 1956 Tornadoes in Western Lower Michigan

An investigation into a historic tornado outbreak in western Lower Michigan yielded several significant findings and provided details about path length, duration, and intensity of each tornado. These findings are presented here, along with discrepancies that were found with the National Climatic Data Center’s storm event database for the number of tornadoes and fatalities that occurred in this event. Potential strategies in forensic meteorology for future studies of historic tornado events also are presented, including suggestions for gathering and synthesizing data. Finally, strategies are discussed for using anniversary events to increase public awareness of severe weather.

On the use of areal coverage of parameters favorable for severe weather to discriminate major outbreaks

Forecaster perceptions of major convective outbreaks include the notion that these events occur within relatively large regions of meteorological conditions favorable for the development of significant severe weather, particularly tornadoes. With recent studies developing a rigorous and scientifically repeatable method of identifying these events and distinguishing them from intermediate or marginal severe weather outbreaks, the investigation of a large sample of these events now is possible. This diagnostic study aims to determine the extent to which the use of areal coverage is successful as a means of discriminating major severe weather outbreaks (primarily but not exclusively major tornado outbreaks) from the less significant outbreaks. Preliminary findings suggest that the areal coverage of severe weather parameters favorable for severe weather indeed is associated with the severity of outbreaks. However, the method produces a substantial number of less significant outbreaks that are misclassified as major severe weather outbreaks. Many of these false alarms can be identified by the presence of synoptic environments that are less favorable for the development of a large number of tornadoes. However, a substantial number of intermediate and marginal severe weather outbreaks feature synoptic patterns and mesoscale environments that are difficult to differentiate from the major events. Limitations of using areal coverage as a means of outbreak discrimination are discussed, and refinements to account for these limitations are proposed.

Identifying Risk and Resilience Factors Impacting Mental Health among Black and Latinx Adults following Nocturnal Tornadoes in the U.S. Southeast.

Prior research has found that Black and Latinx communities in the U.S. face significant disparities that impact both preparedness for severe weather events and the support received after a disaster has occurred. In the current study, we examined key risk and protective factors that impacted mental health among 221 Black and Latinx adult respondents exposed to the 2–3 March 2020 nocturnal tornado outbreak in the U.S. state of Tennessee. Key factors that adversely affected mental health among participants were encountering barriers for receiving tornado warning alerts and tornado-related exposure. Key factors that served a protective mechanism against adverse mental health included having access to physical resources, supportive relationships, and adaptive coping skills. These findings may assist National Weather Service (NWS) personnel, emergency managers, and mental health providers with the development of policies and practices to address barriers and promote protective strategies for future nocturnal tornado events.

Examining the Relationship between Tropopause Polar Vortices and Tornado Outbreaks

AbstractMid-latitude jet streaks are known to produce conditions broadly supportive of tornado outbreaks, including forcing for large-scale ascent, increased wind shear, and decreased static stability. Although many processes may initiate a jet streak, we focus here on the development of jet maxima by interactions between the polar jet and tropopause polar vortices (TPVs). Originating from the Arctic, TPVs are long-lived circulations on the tropopause, which can be advected into the mid-latitudes. We hypothesize that when these vortices interact with the jet, they may contribute supplemental forcing for ascent and shear to tornado outbreaks, assuming other environmental conditions supportive of tornado development exist. Using a case set of significant tornado outbreak days from three states—Oklahoma, Illinois, and Alabama—we show that a vortex-jet streak structure is present (within 1250 km) in around two-thirds of tornado outbreaks. These vortices are commonly Arctic in origin (i.e., are TPVs) and are advected through a consistent path of entry into the mid-latitudes in the week before the outbreak, moving across the Northern Pacific and into the Gulf of Alaska before turning equatorward along the North American coast. These vortices are shown to be more intense and longer-lived than average. We further demonstrate that statistically significant patterns of wind shear, quasi-geostrophic forcing for ascent, and low static stability are present over the outbreak regions on the synoptic scale. In addition, we find that TPVs associated with tornadic events occur most often in the spring and are associated with greater low-level moisture when compared to non-tornadic TPV cases.

The Evolving Weather Service: Forecasters’ Perceptions of Their Relationships with Core Partners

AbstractSince the tragic tornado outbreaks in central Alabama and Joplin, Missouri, in 2011, the National Weather Service (NWS) has increasingly emphasized the importance of supporting community partners who help to protect public safety. Through impact-based decision support services (IDSS), NWS forecasters develop relationships with their core partners to meet their partners’ decision-making needs. IDSS presents a fundamental shift in NWS forecasting through highlighting the importance of connecting with partners instead of simply providing partners with forecasts. A critical challenge to the effective implementation of IDSS is a lack of social science research evaluating the success of IDSS. This paper addresses this gap through a cross-sectional survey with 119 NWS forecasters and managers in the central and southern regions of the United States. Findings uncover how NWS forecasters and management team members evaluate the importance of IDSS. Findings also provide a new instrument for NWS field offices to assess and improve their relationships with core partners.

Environmental analysis on the first documented tornado outbreak in China

AbstractThis study presents an analysis on the storm environmental features during the first recorded tornado outbreak in the modern history of China on August 13–14, 2018. Eleven reported tornadoes were spawned within a 20‐hr period by Typhoon Yagi (1814) during its dissipating stage after its landfall. They primarily formed when Yagi was at a relatively weak intensity. Six tornadoes were generated after that Yagi had lost its intensity as a tropical depression. These tornadoes were mainly located in the northeast quadrant with respect to the typhoon center. Specifically, they were concentrated in the overlapping region of the large storm relative helicity (SRH) and large entraining convective available potential energy (E‐CAPE) that considers the effects of the environmental air entrainment. The intrusion of midlevel dry air was responsible for the spatial pattern of large‐value E‐CAPE. Special focus was further put into the dynamical diagnosis of the cause that the maxima in SRH were distributed in Yagi's northeast sector. On cylindrical coordinates, the northeast quadrant was characterized by the strongest upward increase in the radial velocity in a layer of 950–700 hPa, which resulted from the interaction between the typhoon circulation and the subtropical high and a midlevel trough. The resultant in‐up‐out radial wind profile contributed to the large helicity in the northeast quadrant. In the lowest 50 hPa layer, the helicity was mainly owed to the upward increase in the tangential velocity associated with typhoon vortex. The diagnoses of the atmospheric environment for the tornado outbreak in this case may provide additional benefit for assessing the tornado risk within landfalling tropical cyclones in China.

What Is a Tornado Outbreak?: Perspectives through Time

AbstractThe term “tornado outbreak” appeared in the meteorological literature in the 1950s and was used to highlight severe weather events with multiple tornadoes. The exact meaning of “tornado outbreak,” however, evolved over the years. Depending on the availability of scientific data, technological advancements, and the intended purpose of these definitions, authors offered a diverse set of approaches to shape the perception and applications of the term “tornado outbreak.” This paper reviews over 200 peer-reviewed publications—by decade—to outline the evolving nature of the “tornado outbreak” definition and to examine the changes in the “tornado outbreak” definition or its perception. A final discussion highlights the importance, limitations, and potential future evolution of what defines a “tornado outbreak.”

National Weather Service Severe Weather Warnings as Threats-in-Motion

AbstractThreats-in-Motion (TIM) is a warning generation approach that would enable the NWS to advance severe thunderstorm and tornado warnings from the current static polygon system to continuously updating polygons that move forward with a storm. This concept is proposed as a first stage for implementation of the Forecasting a Continuum of Environmental Threats (FACETs) paradigm, which eventually aims to deliver rapidly updating probabilistic hazard information alongside NWS warnings, watches, and other products. With TIM, a warning polygon is attached to the threat and moves forward along with it. This provides more uniform, or equitable, lead time for all locations downstream of the event. When forecaster workload is high, storms remain continually tracked and warned. TIM mitigates gaps in warning coverage and improves the handling of storm motion changes. In addition, warnings are automatically cleared from locations where the threat has passed. This all results in greater average lead times and lower average departure times than current NWS warnings, with little to no impact to average false alarm time. This is particularly noteworthy for storms expected to live longer than the average warning duration (30 or 45 min) such as long-tracked supercells that are more prevalent during significant tornado outbreaks.

Direct Injuries and Fatalities of Texas Tornado Outbreaks from 1973 to 2007

Since 1950, tornadoes have accounted for nearly one third of disaster-related fatalities in the United States, the third highest after floods and lightning. The largest share of fatalities occurred in the state of Texas, which also accounts for about 7 percent of the overall property damage from tornadoes. An increasing proportion of tornadoes occur during tornado outbreaks, which were responsible for almost 80 percent of tornado-related fatalities in the United States between 1972 and 2010. Although the relationships between tornado severity, economic damage, and injuries and fatalities are generally well understood, few studies examine how injuries and fatalities are affected by a single tornado versus those that are part of a tornado outbreak. This work analyzes a data set of Texas tornadoes that occurred between January 1973 and January 2007, through nonparametric statistical and spatial analyses, examining the associations between tornado severity, number, and geography of occurrence as related to direct injuries and fatalities in severe weather events. Results indicate that tornado severity exacerbates causalities, but outbreaks do have some effect as well. These findings have potential implications for improving forecasting, warning, and preparedness for tornado outbreaks, which could be critical to reducing deaths and injuries from future tornadoes.

U.S. Weather Highlights 2020: The Most Extreme Year on Record?

All the weather cliches applied this year. Yes, this really was “one for the record books” and a “year of weather extremes.” Notable events included winter storms, historical tornado outbreaks, Wes...

The Chilean Tornado Outbreak of May 2019: Synoptic, Mesoscale, and Historical Contexts

AbstractIn late May 2019, at least seven tornadoes were reported within a 24-h period in southern Chile (western South America, 36°–38°S), including EF1 and EF2 events causing substantial damage to infrastructure, dozens of injuries, and one fatality. Despite anecdotal evidence and chronicles of similar historical events, the threat from tornadoes in Chile was regarded with skepticism until the 2019 outbreak. Herein, we describe the synoptic-scale features instrumental in the development of these tornadic storms, including an extended southwest–northeast trough along the South Pacific, with a large postfrontal instability area. Tornadic storms appear to be embedded in a modestly unstable environment (positive convective available potential energy but less than 1,000 J kg−1) and strong low- and midlevel wind shear, with high near-surface storm-relative helicity values (close to −200 m2 s−2), clearly differing from the Great Plains tornadoes in North America (with highly unstable environments) but resembling cold-season tornadoes previously observed in the midlatitudes of North America, Australia, and Europe. Reanalyzing rainfall and lightning data from the last 10 years, we found that tornadic storms in our region occur associated with locally extreme values of both CAPE and low-level wind shear, where a combination of the two in a low-level vorticity generation parameter appears as a simple first-order discriminant between tornadic and nontornadic environments. Future research should thoroughly examine historical events worldwide to assemble a database of high-shear, low-CAPE midlatitude storms and help improve our understanding of these storms’ underlying physics.

Use of Power Transform Mixing Ratios as Hydrometeor Control Variables for Direct Assimilation of Radar Reflectivity in GSI En3DVar and Tests with Five Convective Storm Cases

AbstractWhen directly assimilating radar data within a variational framework using hydrometeor mixing ratios (q) as control variables (CVq), the gradient of the cost function becomes extremely large when background mixing ratio is close to zero. This significantly slows down minimization convergence and makes the assimilation of radial velocity and other observations ineffective because of the dominance of the reflectivity observation term in the cost function gradient. Using logarithmic hydrometeor mixing ratios as control variables (CV logq) can alleviate the problem but the high nonlinearity of logarithmic transformation can introduce spurious analysis increments into mixing ratios. In this study, power transform of hydrometeors is proposed to form new control variables (CVpq) where the nonlinearity of transformation can be adjusted by a tuning exponent or power parameter p. The performance of assimilating radar data using CVpq is compared with those using CVq and CV logq for the analyses and forecasts of five convective storm cases from the spring of 2017. Results show that CVpq with p = 0.4 (CVpq0.4) gives the best reflectivity forecasts in terms of root-mean-square error and equitable threat score. Furthermore, CVpq0.4 has faster convergence of cost function minimization than CVq and produces less spurious analysis increment than CV logq. Compared to CVq and CV logq, CVpq0.4 has better skills of 0–3-h composite reflectivity forecasts, and the updraft helicity tracks for the 16 May 2017 Texas and Oklahoma tornado outbreak case are more consistent with observations when using CVpq0.4.

Смерчи в российских регионах

New data are presented on tornadoes over land in Russia for the period of 1900–2018 based on various sources. In total, information on 1763 tornadoes was collected, including 993 tornadoes from eyewitness reports on tornado passage and/or associated impacts and 770 tornadoes from satellite data on tornado-induced windthrows. Both single tornadoes and tornado outbreaks, the cases of formation of several tornadoes within one meso- or synoptic-scale system, were reported. On average for 2009– 2018, more than 100 tornadoes are observed in Russia per year, including 15 significant tornadoes (with a wind speed >50 m/s) and one intense tornado (with a wind speed >70 m/s). In some years, these rates can be significantly higher and reach 342, 52, and three tornadoes per year, respectively. Tornadoes are observed on about 41 days per year, up to 68 days per annum in some years. The frequency of occurrence of tornadoes of different categories and the probability of their passage over a point on the ground were estimated. These estimates can be further used to assess a risk of tornado-hazardous situations. The general underestimation of the number of tornadic events in routine meteorological observations and existent statistics is discussed.

An Idealized Physical Model for the Severe Convective Storm Environmental Sounding

AbstractThis work develops a theoretical model for steady thermodynamic and kinematic profiles for severe convective storm environments, building off the two-layer static energy framework developed in work by Agard and Emanuel. The model is phrased in terms of static energy, and it allows for independent variation of the boundary layer and free troposphere separated by a capping inversion. An algorithm is presented to apply the model to generate a sounding for numerical simulations of severe convective storms, and the model is compared and contrasted with that of Weisman and Klemp. The model is then fit to a case-study sounding associated with the 3 May 1999 tornado outbreak, and its potential utility is demonstrated via idealized numerical simulation experiments. A long-lived supercell is successfully simulated with the historical sounding but not the analogous theoretical sounding. Two types of example experiments are then performed that do simulate a long-lived supercell: 1) a semitheoretical experiment in which a portion of the theoretical sounding is modified to match the real sounding (low-level moisture); 2) a fully theoretical experiment in which a model physical parameter is modified (free-tropospheric relative humidity). Overall, the construction of this minimal model is flexible and amenable to additional modifications as needed. The model offers a novel framework that may be useful for testing how severe convective storms depend on the vertical structure of the hydrostatic environment, as well as for linking variability in these environments to the physical processes that produce them within the climate system.