Multiple Tornadoes Research Articles

A Stochastic Statistical Model for U.S. Outbreak-Level Tornado Occurrence Based on the Large-Scale Environment

Abstract Tornado outbreaks—when multiple tornadoes occur within a short period of time—are rare yet impactful events. Here we developed a two-part stochastic tornado outbreak index for the contiguous United States (CONUS). The first component produces a probability map for outbreak tornado occurrence based on spatially resolved values of convective precipitation, storm relative helicity (SRH), and convective available potential energy. The second part of the index provides a probability distribution for the total number of tornadoes given the outbreak tornado probability map. Together these two components allow stochastic simulation of location and number of tornadoes that is consistent with environmental conditions. Storm report data from the Storm Prediction Center for the 1979–2021 period are used to train the model and evaluate its performance. In the first component, the probability of an outbreak-level tornado is most sensitive to SRH changes. In the second component, the total number of CONUS tornadoes depends on the sum and gridpoint maximum of the probability map. Overall, the tornado outbreak index represents the climatology, seasonal cycle, and interannual variability of tornado outbreak activity well, particularly over regions and seasons when tornado outbreaks occur most often. We found that El Niño–Southern Oscillation (ENSO) modulates the tornado outbreak index such that La Niña is associated with enhanced U.S. tornado outbreak activity over the Ohio River Valley and Tennessee River Valley regions during January–March, similar to the behavior seen in storm report data. We also found an upward trend in U.S. tornado outbreak activity during winter and spring for the 1979–2021 period using both observations and the index. Significance Statement Tornado outbreaks are when multiple tornadoes happen in a short time span. Because of the rare, sporadic nature of tornadoes, it can be challenging to use observational tornado reports directly to assess how climate affects tornado and tornado outbreak activity. Here, we developed a statistical model that produces a U.S. map of the likelihood that an outbreak-level tornado would occur based on environmental conditions. In addition, using that likelihood map, the model predicts a range of how many tornadoes could occur in these events. We found that “storm relative helicity” (a proxy for potential rotation in a storm’s updraft) is especially important for predicting outbreak tornado likelihood, and the sum and maximum value of the likelihood map is important for predicting total numbers for an event. Overall, this model can represent the typical behavior and fluctuations in tornado outbreak activity well. Both the tornado outbreak model and observations agree that the state of sea surface temperature in the tropical Pacific (El Niño–Southern Oscillation) is linked to tornado outbreak activity over the Ohio River Valley and Tennessee River Valley in winter through early spring and that there are upward trends in tornado outbreak activity.

Analysis of a multiple non-supercell tornado event in Mexico

Multiple tornado events frequently occur in different parts of the world. A region that seems favorable for recurring multiple tornado events due to its geographical location and topography is the eastern sector of the Trans-Mexican Volcanic Belt. A notable multiple tornado event that occurred in this region is investigated. It consisted of five simultaneous tornadoes during the convergence of three air masses: a cold air mass displaced from the north with moderately high relative humidity and specific humidity, a comparatively warm air mass with moderate relative humidity from the southeast, and a hotter air mass with low relative humidity from the southwest. This situation generated a line of intense horizontal wind shear through which the five tornadoes occurred. Numerical simulations revealed three cyclonic vortices and other minor disturbances along the shear line. Vertical cross-sections show rising air in these disturbances suggesting a cyclonic character. The results indicate that the relatively warm mass from the southeast moves over the one associated with a cold front coming from the north, generating multiple cyclonic rotation zones. Experiments with Lagrangian particles revealed vertical movements in the cyclonic rotation zones implying that the maximum heights of the tornadoes varied between 1000 and 1500 m. Moisture flux convergence calculations display structures resembling Kelvin-Helmholtz instabilities. This research proposes a conceptual model where the convergence of masses induced by topography can lead to multiple tornado generation.

Analyzing Tornado Warning Performance during Individual Storm Life Cycles

Abstract The National Weather Service plays a critical role in alerting the public when dangerous weather occurs. Tornado warnings are one of the most publicly visible products the NWS issues given the large societal impacts tornadoes can have. Understanding the performance of these warnings is crucial for providing adequate warning during tornadic events and improving overall warning performance. This study aims to understand warning performance during the lifetimes of individual storms (specifically in terms of probability of detection and lead time). For example, does probability of detection vary based on if the tornado was the first produced by the storm, or the last? We use tornado outbreak data from 2008 to 2014, archived NEXRAD radar data, and the NWS verification database to associate each tornado report with a storm object. This approach allows for an analysis of warning performance based on the chronological order of tornado occurrence within each storm. Results show that the probability of detection and lead time increase with later tornadoes in the storm; the first tornadoes of each storm are less likely to be warned and on average have less lead time. Probability of detection also decreases overnight, especially for first tornadoes and storms that only produce one tornado. These results are important for understanding how tornado warning performance varies during individual storm life cycles and how upstream forecast products (e.g., Storm Prediction Center tornado watches, mesoscale discussions, etc.) may increase warning confidence for the first tornado produced by each storm. Significance Statement In this study, we focus on better understanding real-time tornado warning performance on a storm-by-storm basis. This approach allows us to examine how warning performance can change based on the order of each tornado within its parent storm. Using tornado reports, warning products, and radar data during tornado outbreaks from 2008 to 2014, we find that probability of detection and lead time increase with later tornadoes produced by the same storm. In other words, for storms that produce multiple tornadoes, the first tornado is generally the least likely to be warned in advance; when it is warned in advance, it generally contains less lead time than subsequent tornadoes. These findings provide important new analyses of tornado warning performance, particularly for the first tornado of each storm, and will help inform strategies for improving warning performance.

Infrasound and Low-Audible Acoustic Detections from a Long-Term Microphone Array Deployment in Oklahoma

A three-microphone acoustic array (OSU1), with microphones that have a flat response from 0.1 to 200 Hz, was deployed for 6 years (2016–2022) at Oklahoma State University (OSU) in Stillwater, Oklahoma, and sampled at 1000 Hz. This study presents a new dataset of acoustic measurements in a high interest region (e.g., study of tornado infrasound), provides a broad overview of acoustic detections and the means to identify them, and provides access to these recordings to the broader scientific community. A wide variety of infrasound and low-audible sources were identified and characterized via analysis of time traces, power spectral densities, spectrograms, and beamforming. Low, median, and high noise models were compared with global noise models. Detected sources investigated include natural (microbaroms, bolides, earthquakes, and tornadoes) and anthropomorphic (fireworks, airplanes, and munition detonations) phenomena. Microbarom detections showed consistency with literature (~0.2 Hz with peak amplitude in the winter) and evidence that the frequency was inversely related to the amplitude. Fireworks and airplanes served as verified local events for the evaluation of data quality and processing procedures. Infrasound from munition detonations, that occur nearly daily at a location 180 km southeast of OSU1, matched the available ground truth on days with favorable propagation to OSU1. A clear bolide detection with an estimated position of approximately 300 km from OSU1 was shown. Most detected earthquakes were seismic arrivals due to sensor vibrations; however, the largest earthquake in Oklahoma history showed an acoustic arrival. Finally, data from multiple tornadoes are discussed, including a previously unpublished quasi-linear convective system tornado.

Guiding the optical vortex along predesigned parabolic trajectories from circular symmetric Airy-like beams.

In this paper, by phase-modulating an optical wavefront on circular symmetric Airy vortex beams, we present the circular symmetric Airy-like vortex beams propagating along predesigned parabolic trajectories. Our result shows that we can realize the propagation of an optical vortex with a closed ring lobe along an accelerating parabolic trajectory within a certain propagation distance by using this kind of phase-modulated circular symmetric Airy beam. The vortex that is superimposed on the beams is able to reproduce after being blocked. Additionally, a single twisted dark channel or multiple tornado dark channels with orbital angular momentum rotating along the predesigned parabolic trajectories can also be formed when we impose the off-axis optical vortex on this kind of beam, which has potential in applications of light capturing.

Multiple tornadoes in the Italian Ionian regions: Observations, sensitivity tests and mesoscale analysis of convective storm environmental parameters

In the months of November 2012, 2014 and 2018, four tornadic events affected southern Italy (Calabria and Apulia regions). Tornado-spawning supercells hit the same regions, had similar trajectories, and were characterized by common synoptic conditions.The events are analysed through the use of multiple observational tools; large-scale and mesoscale analysis are performed, in addition to high-resolution numerical simulations and sensitivity tests with the WRF model. In particular, the effect of changes in Sea Surface Temperature on the intensity and tracking of tornadic supercells in the Mediterranean is investigated, finding that small variations of SST may cause significant changes on instability parameters, consequently on the supercell intensity.Numerical simulations show that the structure and the track of the convective cells can be correctly reproduced, as well as the triggering of convection due to interaction of the flow with the topographic features, such as the land-sea interface and orography, within a relatively small temporal delay. The mesoscale analysis also reveals, in all cases, an environment highly favourable for tornado formation, with most simulated instability parameters/indices exceeding their critical thresholds.

Examining sub-daily tornado warning performance and associated environmental characteristics

AbstractIncreasing tornado warning skill in terms of the probability of detection and false alarm ratio remains an important operational goal. Although many studies have examined tornado warning performance in a broad sense, less focus has been placed on warning performance within sub-daily convective events. In this study, we use the NWS tornado verification database to examine tornado warning performance by order-of-tornado within each convective day. We combine this database with tornado reports to relate warning performance to environmental characteristics. On convective days with multiple tornadoes, the first tornado is warned significantly less often than the middle and last tornadoes. More favorable kinematic environmental characteristics, like increasing 0–1-km shear and storm-relative helicity, are associated with better warning performance related to the first tornado of the convective day. Thermodynamic and composite parameters are less correlated to warning performance. During tornadic events, over half of false alarms occur after the last tornado of the day decays, and false alarms are twice as likely to be issued during this time than before the first tornado forms. These results indicate that forecasters may be better “primed” (or more prepared) to issue warnings on middle and last tornadoes of the day, and must overcome a higher threshold to warn on the first tornado of the day. To overcome this challenge, using kinematic environmental characteristics and intermediate products on the watch-to-warning scale may help.

Differences in tornado activities and key tornadic environments between China and the United States

AbstractThe yearly tornado occurrence in China is approximately 5–10% of that in the United States, and the peak month of tornado occurrence in China is July, while that in the United States is May. However, the two countries have nearly the same land area and similar latitudinal location. This study attempts to disclose the differences in the key tornadic environments that are most possibly responsible for the large discrepancy of tornado occurrences observed between the two countries. The region with the highest tornado density in China (JS) is compared with three similarly sized regions in the United States, including two tornado‐prone regions (UC and USE1) and one region similar to JS (USE2). The results show that JS has a much lower tornado frequency than UC and USE1, mainly due to JS's much lower likelihood of multiple tornadoes occurring in a short period during its tornado season. Compared with UC and USE1, JS features relatively low mean values of the significant tornado parameter (STP) during their respective tornado seasons. The STP, incorporating several tornado‐related variables, was found to show a monotonic relationship with the total tornado count at a seasonal scale and perform well to explain monthly variations in tornado frequencies. Compared with the target regions in the United States, JS has a similar magnitude and decreasing trend of the 0–6‐km vertical wind shear from spring to summer, but a later increase in instability. Resulting from a balance between the decreasing vertical shear and the increasing thermodynamic instability, JS features a delayed monthly peak of STP and thus a delayed tornado season, which makes JS having a worse kinematic environment for tornadogenesis with far lower low‐level vertical wind shear during its tornado season than that of the United States.

Australian Tornadoes in 2013: Implications for Climatology and Forecasting

AbstractDuring 2013, multiple tornadoes occurred across Australia, leading to 147 injuries and considerable damage. This prompted speculation as to the frequency of these events in Australia, and whether 2013 constituted a record year. Leveraging media reports, public accounts, and the Bureau of Meteorology observational record, 69 tornadoes were identified for the year in comparison to the official count of 37 events. This identified set and the existing historical record were used to establish that, in terms of spatial distribution, 2013 was not abnormal relative to the existing climatology, but numerically exceeded any year in the bureau’s record. Evaluation of the environments in which these tornadoes formed illustrated that these conditions included tornado environments found elsewhere globally, but generally had a stronger dependence on shear magnitude than direction, and lower lifting condensation levels. Relative to local environment climatology, 2013 was also not anomalous. These results illustrate a range of tornadoes associated with cool season, tropical cyclone, east coast low, supercell tornado, and low shear/storm merger environments. Using this baseline, the spatial climatology from 1980 to 2019 as derived from the nonconditional frequency of favorable significant tornado parameter environments for the year is used to highlight that observations are likely an underestimation. Applying the results, discussion is made of the need to expand observing practices, climatology, forecasting guidelines for operational prediction, and improve the warning system. This highlights a need to ensure that the general public is appropriately informed of the tornado hazard in Australia, and provide them with the understanding to respond accordingly.

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.”

Structural Observations and Tornado Damage Mitigation Concepts: March 2020 Tennessee Tornadoes

AbstractEarly in the morning of March 3, 2020, a storm system producing multiple tornadoes passed through middle Tennessee. One of the tornadoes—touching down in Cookeville and Putnam County—was cl...

A Case Study of Tsukuba Tornado in Japan on 6 May 2012

This study conducted synoptic and mesoscale analyses to understand the cause of Japan Tsukuba tornado development, which occurred at 0340 UTC 6 May 2012. Prior to the tornado occurrence, there was a circular jet stream over Japan, and the surface was moist due to overnight precipitation. The circular jet stream brought cold and dry air to the upper-level atmosphere which let strong solar radiation heat the ground with clearing of sky cover. A tornadic supercell developed in the area of potentially unstable atmosphere. Sounding data at Tateno showed a capping inversion at 900 hPa at 0000 UTC 6 May. Strong insolation in early morning hours and removal of the inversion instigated vigorous updraft with rotation due to vertical shear in the upper-level atmosphere. This caused multiple tornadoes to occur from 0220 to 0340 UTC 6 May 2012. When comparing Tateno’s climatological temperature and dew-point temperature profile on the day of event, the mid-level atmosphere was moister than typical sounding in the region. This study showed that tornado development in Tsukuba was caused by a combination of (a) topography and potential vorticity anomaly, which increased vorticity over the Kanto Plain; (b) vertical shear, which produced horizontal vortex line; and c) thermal instability, which triggered supercell and tilted the vortex line in the vertical.

Explicating Experience: Development of a Valid Scale of Past Hazard Experience for Tornadoes.

People's past experiences with a hazard theoretically influence how they approach future risks. Yet, past hazard experience has been conceptualized and measured in wide-ranging, often simplistic, ways, resulting in mixed findings about its relationship with risk perception. This study develops a scale of past hazard experiences, in the context of tornadoes, that is content and construct valid. A conceptual definition was developed, a set of items were created to measure one's most memorable and multiple tornado experiences, and the measures were evaluated through two surveys of the public who reside in tornado-prone areas. Four dimensions emerged of people's most memorable experience, reflecting their awareness of the tornado risk that day, their personalization of the risk, the intrusive impacts on them personally, and impacts experienced vicariously through others. Two dimensions emerged of people's multiple experiences, reflecting common types of communication received and negative emotional responses. These six dimensions are novel in that they capture people's experience across the timeline of a hazard as well as intangible experiences that are both direct and indirect. The six tornado experience dimensions were correlated with tornado risk perceptions measured as cognitive-affective and as perceived probability of consequences. The varied experience-risk perception results suggest that it is important to understand the nuances of these concepts and their relationships. This study provides a foundation for future work to continue explicating past hazard experience, across different risk contexts, and for understanding its effect on risk assessment and responses.

複数同時発生する竜巻をもたらす温帯低気圧と梅雨前線上の低気圧

複数同時発生する竜巻をもたらす温帯低気圧と梅雨前線上の低気圧

Tornado outbreak variability follows Taylor's power law of fluctuation scaling and increases dramatically with severity.

Tornadoes cause loss of life and damage to property each year in the United States and around the world. The largest impacts come from ‘outbreaks' consisting of multiple tornadoes closely spaced in time. Here we find an upward trend in the annual mean number of tornadoes per US tornado outbreak for the period 1954–2014. Moreover, the variance of this quantity is increasing more than four times as fast as the mean. The mean and variance of the number of tornadoes per outbreak vary according to Taylor's power law of fluctuation scaling (TL), with parameters that are consistent with multiplicative growth. Tornado-related atmospheric proxies show similar power-law scaling and multiplicative growth. Path-length-integrated tornado outbreak intensity also follows TL, but with parameters consistent with sampling variability. The observed TL power-law scaling of outbreak severity means that extreme outbreaks are more frequent than would be expected if mean and variance were independent or linearly related.

Topological study of steady state, three dimensional flow over a backward facing step

The topology and evolution of flow over a backward facing step in three dimensional channel flow is examined from creeping flow conditions up to Re=950 with aspect ratio 1:40 and expansion ratio 1:2. Direct numerical simulations were performed via the parallel finite element code “FEM-3D”. Analysis of the results is performed using the three dimensional theory of separation. Results reveal the existence of a primary spanwise vortex that emanates from the lateral wall and is present for all Reynolds numbers immediately downstream from the step. Frictional (shear) stresses along the lateral wall create multiple tornado like vortices. Another spanwise vortex along the top wall appears at Re=400. As the Reynolds number increases, the top vortex increases both in spanwise and streamwise length and stunts the growth of the primary vortex. The downstream motion of the top vortex releases frictional stress thus destroying some critical points upstream while creating new ones downstream. Finally, at Re=900 and 950, the primary and top vortices are twisting severely.

Tornadoes clustering in greater numbers

Climate Change![Figure][1] Tornado traveling across a plain CREDITS: JOHN LUNG/GETTY IMAGES Will global warming cause more tornadoes? If so, that has not happened yet. Brooks et al. compiled data on the occurrence of tornadoes in the United States between 1954 and 2013 to determine if and how tornado numbers have changed. Although the authors saw no clear trend in the annual number of tornadoes, they did see more clusters of tornadoes since the 1970s. In other words, there has been a decrease in the number of days per year with tornadoes but an increase in the number of days with multiple tornadoes. Why this clustering effect has occurred is not clear. Science , this issue p. [349][2] [1]: pending:yes [2]: /lookup/doi/10.1126/science.1257460

Assessment of the wind hazard due to tornado outbreaks in southern Ontario

A tornado outbreak is a severe weather event that involves the occurrence of multiple tornadoes in a short period of time in a region. Although widespread damage has been associated with many historical outbreaks, wind hazard assessments, and the methodology for making such assessments, are lacking in the literature. The current study addresses this by developing a probabilistic simulation-based approach and then applying it to southern Ontario, using a model for the outbreak characteristics based on the tornado database for the regions neighboring southern Ontario and the tornado characteristics obtained from historical occurrences of tornadoes in southern Ontario. A quantitative assessment of the outbreak hazard for an area representing an idealized city in southern Ontario was carried out and the results are compared with those obtained by ignoring the outbreak phenomenon. The comparison shows that ignoring outbreaks can lead to an order of magnitude decrease in hazard estimates when an accumulated damage area of 100km2 or more is of concern.

Convection-Allowing and Convection-Parameterizing Ensemble Forecasts of a Mesoscale Convective Vortex and Associated Severe Weather Environment

Abstract An analysis of a regional severe weather outbreak that was related to a mesoscale convective vortex (MCV) is performed. The MCV-spawning mesoscale convection system (MCS) formed in northwest Kansas along the southern periphery of a large cutoff 500-hPa low centered over western South Dakota. As the MCS propagated into eastern Kansas during the early morning of 1 June 2007, an MCV that became evident from multiple data sources [e.g., Weather Surveillance Radar-1988 Doppler (WSR-88D) network, visible satellite imagery, wind-profiler data, Rapid Update Cycle 1-hourly analyses] tracked through northwest Missouri and central Iowa and manifested itself as a well-defined midlevel short-wave trough. Downstream of the MCV in southeast Iowa and northwest Illinois, southwesterly 500-hPa winds increased to around 25 m s−1 over an area with southeasterly surface winds and 500–1500 J kg−1 of surface-based convective available potential energy (CAPE), creating a favorable environment for severe weather. In the favorable region, multiple tornadoes occurred, including one rated as a category 3 storm on the enhanced Fujita scale (EF3) that caused considerable damage. In the analysis, emphasis is placed on the role of the MCV in leading to a favorable environment for severe weather. In addition, convection-allowing forecasts of the MCV and associated environmental conditions from the 10-member Storm-Scale Ensemble Forecast (SSEF) system produced for the 2007 NOAA Hazardous Weather Testbed Spring Experiment are compared to those from a similarly configured, but coarser, 30-member convection-parameterizing ensemble. It was found that forecasts of the MCV track and associated environmental conditions (e.g., midlevel winds, low-level wind shear, and instability) were much better in the convection-allowing ensemble. Errors in the MCV track from convection-parameterizing members likely resulted from westward displacement errors in the incipient MCS. Furthermore, poor depiction of MCV structure and maintenance in convection-parameterizing members, which was diagnosed through a vorticity budget analysis, likely led to the relatively poor forecasts of the associated environmental conditions. The results appear to be very encouraging for convection-allowing ensembles, especially when environmental conditions lead to a high degree of predictability for MCSs, which appeared to be the case for this particular event.

NWS Tornado Warnings with Zero or Negative Lead Times

Abstract During a 5-yr period of study from 2000 to 2004, slightly more than 10% of all National Weather Service (NWS) tornado warnings were issued either simultaneously as the tornado formed (i.e., with zero lead time) or minutes after initial tornado formation but prior to tornado dissipation (i.e., with “negative” lead time). This study examines why these tornadoes were not warned in advance, and what climate, storm morphology, and sociological factors may have played a role in delaying the issuance of the warning. This dataset of zero and negative lead time warnings are sorted by their F-scale ratings, geographically by region and weather forecast office (WFO), hour of the day, month of the year, tornado-to-radar distance, county population density, and number of tornadoes by day, hour, and order of occurrence. Two key results from this study are (i) providing advance warning on the first tornado of the day remains a difficult challenge and (ii) the more isolated the tornado event, the less likelihood that an advance warning is provided. WFOs that experience many large-scale outbreaks have a lower proportion of warnings with negative lead time than WFOs that experience many more isolated, one-tornado or two-tornado warning days. Monthly and geographic trends in lead time are directly impacted by the number of multiple tornado events. Except for a few isolated cases, the impacts of tornado-to-radar distance, county population density, and storm morphology did not have a significant impact on negative lead-time warnings.