An Analysis of 2016-2018 Tornadoes and National Weather Service Tornado Warnings across the contiguous United States

2021 ◽  
Author(s):  
Evan S. Bentley ◽  
Richard L. Thompson ◽  
Barry R. Bowers ◽  
Justin G. Gibbs ◽  
Steven E. Nelson
Keyword(s):  
United States ◽  
Rotational Velocity ◽  
Radar Data ◽  
Probability Of Detection ◽  
False Alarms ◽  
National Weather Service ◽  
Low Level ◽  
Tornado Warnings ◽  
Tornado Warning ◽  
Weather Service

AbstractPrevious work has considered tornado occurrence with respect to radar data, both WSR-88D and mobile research radars, and a few studies have examined techniques to potentially improve tornado warning performance. To date, though, there has been little work focusing on systematic, large-sample evaluation of National Weather Service (NWS) tornado warnings with respect to radar-observable quantities and the near-storm environment. In this work, three full years (2016–2018) of NWS tornado warnings across the contiguous United States were examined, in conjunction with supporting data in the few minutes preceding warning issuance, or tornado formation in the case of missed events. The investigation herein examines WSR-88D and Storm Prediction Center (SPC) mesoanalysis data associated with these tornado warnings with comparisons made to the current Warning Decision Training Division (WDTD) guidance.Combining low-level rotational velocity and the significant tornado parameter (STP), as used in prior work, shows promise as a means to estimate tornado warning performance, as well as relative changes in performance as criteria thresholds vary. For example, low-level rotational velocity peaking in excess of 30 kt (15 m s−1), in a near-storm environment which is not prohibitive for tornadoes (STP > 0), results in an increased probability of detection and reduced false alarms compared to observed NWS tornado warning metrics. Tornado warning false alarms can also be reduced through limiting warnings with weak (<30 kt), broad (>1nm) circulations in a poor (STP=0) environment, careful elimination of velocity data artifacts like sidelobe contamination, and through greater scrutiny of human-based tornado reports in otherwise questionable scenarios.

scholarly journals Long-Term Performance Metrics for National Weather Service Tornado Warnings

2018 ◽  
Vol 33 (6) ◽  
pp. 1501-1511 ◽  
Author(s):  
Harold E. Brooks ◽  
James Correia
Keyword(s):  
False Alarm ◽  
Lead Time ◽  
Performance Metrics ◽  
Warning System ◽  
Probability Of Detection ◽  
False Alarms ◽  
National Weather Service ◽  
False Alarm Ratio ◽  
Tornado Warnings ◽  
Weather Service

Abstract Tornado warnings are one of the flagship products of the National Weather Service. We update the time series of various metrics of performance in order to provide baselines over the 1986–2016 period for lead time, probability of detection, false alarm ratio, and warning duration. We have used metrics (mean lead time for tornadoes warned in advance, fraction of tornadoes warned in advance) that work in a consistent way across the official changes in policy for warning issuance, as well as across points in time when unofficial changes took place. The mean lead time for tornadoes warned in advance was relatively constant from 1986 to 2011, while the fraction of tornadoes warned in advance increased through about 2006, and the false alarm ratio slowly decreased. The largest changes in performance take place in 2012 when the default warning duration decreased, and there is an apparent increased emphasis on reducing false alarms. As a result, the lead time, probability of detection, and false alarm ratio all decrease in 2012. Our analysis is based, in large part, on signal detection theory, which separates the quality of the warning system from the threshold for issuing warnings. Threshold changes lead to trade-offs between false alarms and missed detections. Such changes provide further evidence for changes in what the warning system as a whole considers important, as well as highlighting the limitations of measuring performance by looking at metrics independently.

scholarly journals Tornado Warning Decisions Using Phased-Array Radar Data

2015 ◽  
Vol 30 (1) ◽  
pp. 57-78 ◽  
Author(s):  
Pamela Heinselman ◽  
Daphne LaDue ◽  
Darrel M. Kingfield ◽  
Robert Hoffman
Keyword(s):  
Lead Time ◽  
Phased Array ◽  
Cognitive Task ◽  
Radar Data ◽  
Probability Of Detection ◽  
Probability Of False Alarm ◽  
Temporal Sampling ◽  
Phased Array Radar ◽  
Tornado Warnings ◽  
Tornado Warning

Abstract The 2012 Phased Array Radar Innovative Sensing Experiment identified how rapidly scanned full-volumetric data captured known mesoscale processes and impacted tornado-warning lead time. Twelve forecasters from nine National Weather Service forecast offices used this rapid-scan phased-array radar (PAR) data to issue tornado warnings on two low-end tornadic and two nontornadic supercell cases. Verification of the tornadic cases revealed that forecasters’ use of PAR data provided a median tornado-warning lead time (TLT) of 20 min. This 20-min TLT exceeded by 6.5 and 9 min, respectively, participants’ forecast office and regions’ median spring season, low-end TLTs (2008–13). Furthermore, polygon-based probability of detection ranged from 0.75 to 1.0 and probability of false alarm for all four cases ranged from 0.0 to 0.5. Similar performance was observed regardless of prior warning experience. Use of a cognitive task analysis method called the recent case walk-through showed that this performance was due to forecasters’ use of rapid volumetric updates. Warning decisions were based upon the intensity, persistence, and important changes in features aloft that are precursors to tornadogenesis. Precursors that triggered forecasters’ decisions to warn occurred within one or two typical Weather Surveillance Radar-1988 Doppler (WSR-88D) scans, indicating PAR’s temporal sampling better matches the time scale at which these precursors evolve.

Measuring Tornado Warning Reception, Comprehension, and Response in the United States

2019 ◽  
Vol 11 (4) ◽  
pp. 863-880 ◽  
Author(s):  
Joseph T. Ripberger ◽  
Makenzie J. Krocak ◽  
Wesley W. Wehde ◽  
Jinan N. Allan ◽  
Carol Silva ◽  
...  
Keyword(s):  
United States ◽  
Performance Management ◽  
Source Code ◽  
The United States ◽  
Psychometric Tests ◽  
National Weather Service ◽  
Significant Development ◽  
Tornado Warnings ◽  
Tornado Warning ◽  
Information Domain

Abstract Social criteria are important to achieving the mission of the National Weather Service. Accordingly, researchers and administrators at the NWS increasingly recognize a need to supplement verification statistics with complementary data about society in performance management and evaluation. This will require significant development of new capacities to both conceptualize relevant criteria and measure them using consistent, transparent, replicable, and reliable measures that permit generalizable inference to populations of interest. In this study, we contribute to this development by suggesting three criteria that require measurement (forecast and warning reception, comprehension, and response) and demonstrating a methodology that allows us to measure these concepts in a single information domain—tornado warnings. The methodology we employ improves upon previous research in multiple ways. It provides a more generalizable approach to measurement using a temporally consistent set of survey questions that are applicable across the United States; it relies on a more robust set of psychometric tests to analytically demonstrate the reliability of the measures; and it is more transparent and replicable than previous research because the data and methods (source code) are publicly available. In addition to describing and assessing the reliability of the measures, we explore the sensitivity of the measures to geographic and demographic variation to identify significant differences that require attention in measurement. We close by discussing the implications of this study and the next steps toward development and use of social criteria in performance management and evaluation.

scholarly journals Usefulness of the United States National Weather Service Radar Display as Rated by Website Users

2018 ◽  
Vol 10 (4) ◽  
pp. 673-691 ◽  
Author(s):  
Michelle E. Saunders ◽  
Kevin D. Ash ◽  
Jennifer M. Collins
Keyword(s):  
United States ◽  
Spatial Clustering ◽  
Weather Radar ◽  
Weather Conditions ◽  
Radar Data ◽  
The United States ◽  
Perceived Usefulness ◽  
National Weather Service ◽  
Weather Information ◽  
Weather Service

Abstract Weather radar is now widely viewed by the general public in the United States via television, computers/tablets, and smartphones. Anyone can consult near-real-time maps and animations of weather radar data when weather conditions are a factor. However, the usefulness of weather radar data for each user depends on a complex interaction of factors. There have been few studies providing conceptual arguments and empirical data to better understand what the most important factors are and to comprehend patterns of public weather radar use across the United States. The first part of this research provides a basic conceptual framework for research investigating the usefulness of weather radar displays as a source of weather information and as a decision aid. The second part aims to uncover several factors that influence the perceived usefulness rating of the National Weather Service (NWS) website’s weather radar display at both national and regional levels using variables gathered from the 2014 NWS customer satisfaction survey alongside relevant geographic and climatological variables. Data analyses include spatial clustering and ordinal regression utilized within a generalized linear model methodology. Overall, respondents who are more familiar with the NWS and their products, as well as those who indicate they are more likely to take action based on information provided by the NWS, are more likely to find the NWS radar display useful. Geographically, the NWS radar display is most useful to persons residing in the southern United States. Lightning is the most important hazard associated with higher radar usefulness ratings.

scholarly journals Characteristics of Tornado Events and Warnings in the Southeastern United States

2019 ◽  
Vol 34 (4) ◽  
pp. 1017-1034 ◽  
Author(s):  
Alexandra K. Anderson-Frey ◽  
Yvette P. Richardson ◽  
Andrew R. Dean ◽  
Richard L. Thompson ◽  
Bryan T. Smith
Keyword(s):  
United States ◽  
False Alarm ◽  
Southeastern United States ◽  
Probability Of Detection ◽  
High Shear ◽  
Related Literature ◽  
False Alarm Ratio ◽  
Tornado Warnings ◽  
Tornado Warning

Abstract The southeastern United States has become a prime area of focus in tornado-related literature due, in part, to the abundance of tornadoes occurring in high-shear low-CAPE (HSLC) environments. Through this analysis of 4133 tornado events and 16 429 tornado warnings in the southeastern United States, we find that tornadoes in the Southeast do indeed have, on average, higher shear and lower CAPE than tornadoes elsewhere in the contiguous United States (CONUS). We also examine tornado warning skill in the form of probability of detection (POD; percent of tornadoes receiving warning prior to tornado occurrence) and false alarm ratio (FAR; percent of tornado warnings for which no corresponding tornado is detected), and find that, on average, POD is better and FAR is worse for tornadoes in the Southeast than for the CONUS as a whole. These measures of warning skill remain consistent even when we consider only HSLC tornadoes. The Southeast also has nearly double the CONUS percentage of deadly tornadoes, with the highest percentage of these deadly tornadoes occurring during the spring, the winter, and around local sunset. On average, however, the tornadoes with the lowest POD also tend to be those that are weakest and least likely to be deadly; for the most part, the most dangerous storms are indeed being successfully warned.

scholarly journals Radar Observations of Tornado-Warned Convection Associated with Tropical Cyclones over Florida

2017 ◽  
Vol 32 (1) ◽  
pp. 165-186 ◽  
Author(s):  
Steven M. Martinaitis
Keyword(s):  
False Alarm ◽  
Tropical Cyclones ◽  
Rotational Velocity ◽  
Elevation Angle ◽  
Probability Of Detection ◽  
Polarization Data ◽  
False Alarm Ratio ◽  
Tornado Warnings ◽  
Tornado Warning ◽  
Velocity Enhancement

Abstract Statistical evaluations of tornado warnings issued during recent tropical cyclone events yielded an above-average false alarm ratio. This study analyzed tornado-warned convection associated with Tropical Storms Debby (2012) and Andrea (2013) using superresolution and dual-polarization data from Weather Surveillance Radar-1988 Doppler radars located throughout the Florida peninsula to identify precursor characteristics and signatures that would distinguish tornadic events prior to tornadogenesis. A series of radar-based interrogation guidance at varying ranges from radar is presented to help facilitate the reduction of the tornado-warning false alarm ratio without compromising the probability of detection. For convection within 74.1 km from the nearest radar, low-level velocity characteristics include a rotational velocity ≥ 10.3 m s−1 (20 kt), shear across the rotation ≥ 0.010 s−1, and a contracting rotation diameter. The convection should also exhibit supercell reflectivity signatures and at least a mesocyclone velocity enhancement signature or horizontal separation of greater ZDR and KDP values. Guidance at a range from 74.1 to 129.6 km is similar except for not requiring the presence of a supercell reflectivity signature and the change of the rotational velocity guidance to ≥7.7 m s−1 (15 kt) at the 0.5°-elevation angle. Convection at a range beyond 129.6 km only requires a rotational velocity ≥ 7.7 m s−1 (15 kt) at the 0.5°-elevation angle. Evaluation of the radar interrogation guidance for tornadic events and tornado-warned convection for six tropical cyclones reduced the number of false alarm events by 28.9% and reduced the false alarm ratio from 0.740 to 0.669.

scholarly journals Near-Storm Environments of Outbreak and Isolated Tornadoes

2018 ◽  
Vol 33 (5) ◽  
pp. 1397-1412 ◽  
Author(s):  
Alexandra K. Anderson-Frey ◽  
Yvette P. Richardson ◽  
Andrew R. Dean ◽  
Richard L. Thompson ◽  
Bryan T. Smith
Keyword(s):  
United States ◽  
Great Plains ◽  
Southeastern United States ◽  
Probability Of Detection ◽  
Geographical Region ◽  
Self Organizing Maps ◽  
Specific Shape ◽  
The Difference ◽  
Tornado Warning ◽  
Tornado Outbreaks

Abstract Between 2003 and 2015, there were 5343 outbreak tornadoes and 9389 isolated tornadoes reported in the continental United States. Here, the near-storm environmental parameter-space distributions of these two categories are compared via kernel density estimation, and the seasonal, diurnal, and geographical features of near-storm environments of these two sets of events are compared via self-organizing maps (SOMs). Outbreak tornadoes in a given geographical region tend to be characterized by greater 0–1-km storm-relative helicity and 0–6-km vector shear magnitude than isolated tornadoes in the same geographical region and also have considerably higher tornado warning-based probability of detection (POD) than isolated tornadoes. A SOM of isolated tornadoes highlights that isolated tornadoes with higher POD also tend to feature higher values of the significant tornado parameter (STP), regardless of the specific shape of the area of STP. For a SOM of outbreak tornadoes, when two outbreak environments with similarly high magnitudes but different patterns of STP are compared, the difference is primarily geographical, with one environment dominated by Great Plains and Midwest outbreaks and another dominated by outbreaks in the southeastern United States. Two specific tornado outbreaks are featured, and the events are placed into their climatological context with more nuance than typical single proximity sounding-based approaches would allow.

scholarly journals Cry Wolf Effect? Evaluating the Impact of False Alarms on Public Responses to Tornado Alerts in the Southeastern United States

2019 ◽  
Vol 11 (3) ◽  
pp. 549-563 ◽  
Author(s):  
JungKyu Rhys Lim ◽  
Brooke Fisher Liu ◽  
Michael Egnoto
Keyword(s):  
United States ◽  
False Alarm ◽  
Protective Action ◽  
Southeastern United States ◽  
The United States ◽  
False Alarms ◽  
Protective Behavior ◽  
Tornado Warnings ◽  
Research Findings ◽  
The Impact

Abstract On average, 75% of tornado warnings in the United States are false alarms. Although forecasters have been concerned that false alarms may generate a complacent public, only a few research studies have examined how the public responds to tornado false alarms. Through four surveys (N = 4162), this study examines how residents in the southeastern United States understand, process, and respond to tornado false alarms. The study then compares social science research findings on perceptions of false alarms to actual county false alarm ratios and the number of tornado warnings issued by counties. Contrary to prior research, findings indicate that concerns about false alarm ratios generating a complacent public may be overblown. Results show that southeastern U.S. residents estimate tornado warnings to be more accurate than they are. Participants’ perceived false alarm ratios are not correlated with actual county false alarm ratios. Counterintuitively, the higher individuals perceive false alarm ratios and tornado alert accuracy to be, the more likely they are to take protective behavior such as sheltering in place in response to tornado warnings. Actual country false alarm ratios and the number of tornado warnings issued did not predict taking protective action.

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