scholarly journals Radar Climatology of Tornadic and Nontornadic Vortices in High-Shear, Low-CAPE Environments in the Mid-Atlantic and Southeastern United States

2014 ◽  
Vol 29 (4) ◽  
pp. 828-853 ◽  
Author(s):  
Jason M. Davis ◽  
Matthew D. Parker
Keyword(s):  
United States ◽  
False Alarm ◽  
High Probability ◽  
Southeastern United States ◽  
Vertical Wind Shear ◽  
Probability Of Detection ◽  
Radar Reflectivity ◽  
High Shear ◽  
Convective Systems ◽  
Azimuthal Shear

Abstract Tornadoes occurring in environments characterized by strong vertical wind shear [0–6-km bulk wind difference ≥35 knots (kt; 1 kt = 0.51 m s−1) (18 m s−1)] but low CAPE (<500 J kg−1) are an important challenge for forecasters, especially in the mid-Atlantic and southeastern United States. In this study, 95 tornadic and 135 nontornadic vortices were tracked in high-shear, low-CAPE (HSLC) environments. Values of azimuthal shear were recorded along the vortex tracks, and operationally relevant radar reflectivity signatures were also manually identified in association with these vortices. Statistically significant differences in azimuthal shear were found between tornadic and nontornadic vortices within 60 km of the radar, particularly near the surface. Although there were significant differences between tornadic and nontornadic vortices from nonsupercells (primarily quasi-linear convective systems), this was not the case for supercellular vortices. Beyond 60 km from the radar, no statistically significant differences were found. Numerous reflectivity signatures were also studied, including hook echoes and weak-echo regions associated with supercell vortices, as well as rear-inflow notches, bowing segments, and forward-inflow notches associated with nonsupercell vortices. These signatures were found to have a high probability of detection close to the radar, but also a high false alarm rate, and were observed much less often >100 km from the radar. Overall, while azimuthal shear and radar reflectivity signatures show the potential for high probability of detection in close proximity to operational radars, high false alarm rates, and short lead times appear to be an unavoidable trade-off in HSLC environments.

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 Composite Environments of Severe and Nonsevere High-Shear, Low-CAPE Convective Events

2016 ◽  
Vol 31 (6) ◽  
pp. 1899-1927 ◽  
Author(s):  
Keith D. Sherburn ◽  
Matthew D. Parker ◽  
Jessica R. King ◽  
Gary M. Lackmann
Keyword(s):  
United States ◽  
Boundary Layers ◽  
Vertical Wind Shear ◽  
Probability Of Detection ◽  
High Shear ◽  
Eastern United States ◽  
Detailed Statistical Analysis ◽  
Strong Surface ◽  
Lapse Rates ◽  
Spatial Focusing

Abstract Severe convection occurring in environments characterized by large amounts of vertical wind shear and limited instability (high-shear, low-CAPE, or “HSLC,” environments) represents a considerable forecasting and nowcasting challenge. Of particular concern, NWS products associated with HSLC convection have low probability of detection and high false alarm rates. Past studies of HSLC convection have examined features associated with single cases; the present work, through composites of numerous cases, illustrates the attributes of “typical” HSLC severe and nonsevere events and identifies features that discriminate between the two. HSLC severe events across the eastern United States typically occur in moist boundary layers within the warm sector or along the cold front of a strong surface cyclone, while those in the western United States have drier boundary layers and more typically occur in the vicinity of a surface triple point or in an upslope regime. The mean HSLC severe event is shown to exhibit stronger forcing for ascent at all levels than its nonsevere counterpart. The majority of EF1 or greater HSLC tornadoes are shown to occur in the southeastern United States, so this region is subjected to the most detailed statistical analysis. Beyond the documented forecasting skill of environmental lapse rates and low-level shear vector magnitude, it is shown that a proxy for the release of potential instability further enhances skill when attempting to identify potentially severe HSLC events. This enhancement is likely associated with the local, in situ CAPE generation provided by this mechanism. Modified forecast parameters including this proxy show considerably improved spatial focusing of the forecast severe threat when compared to existing metrics.

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 Can the GPM IMERG Final Product Accurately Represent MCSs’ Precipitation Characteristics over the Central and Eastern United States?

2020 ◽  
Vol 21 (1) ◽  
pp. 39-57 ◽  
Author(s):  
Wenjun Cui ◽  
Xiquan Dong ◽  
Baike Xi ◽  
Zhe Feng ◽  
Jiwen Fan
Keyword(s):  
United States ◽  
False Alarm ◽  
Stage Iv ◽  
Cloud Base ◽  
Eastern United States ◽  
Convective Systems ◽  
Precipitation Measurement ◽  
Precipitation Characteristics ◽  
Mesoscale Convective ◽  
Global Precipitation

AbstractMesoscale convective systems (MCSs) play an important role in water and energy cycles as they produce heavy rainfall and modify the radiative profile in the tropics and midlatitudes. An accurate representation of MCSs’ rainfall is therefore crucial in understanding their impact on the climate system. The V06B Integrated Multisatellite Retrievals from Global Precipitation Measurement (IMERG) half-hourly precipitation final product is a useful tool to study the precipitation characteristics of MCSs because of its global coverage and fine spatiotemporal resolutions. However, errors and uncertainties in IMERG should be quantified before applying it to hydrology and climate applications. This study evaluates IMERG performance on capturing and detecting MCSs’ precipitation in the central and eastern United States during a 3-yr study period against the radar-based Stage IV product. The tracked MCSs are divided into four seasons and are analyzed separately for both datasets. IMERG shows a wet bias in total precipitation but a dry bias in hourly mean precipitation during all seasons due to the false classification of nonprecipitating pixels as precipitating. These false alarm events are possibly caused by evaporation under the cloud base or the misrepresentation of MCS cold anvil regions as precipitating clouds by the algorithm. IMERG agrees reasonably well with Stage IV in terms of the seasonal spatial distribution and diurnal cycle of MCSs precipitation. A relative humidity (RH)-based correction has been applied to the IMERG precipitation product, which helps reduce the number of false alarm pixels and improves the overall performance of IMERG with respect to Stage IV.

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.

Regional, Seasonal, and Diurnal Variations of Cloud-to-Ground Lightning with Large Impulse Charge Moment Changes

2014 ◽  
Vol 142 (10) ◽  
pp. 3666-3682 ◽  
Author(s):  
Nick K. Beavis ◽  
Timothy J. Lang ◽  
Steven A. Rutledge ◽  
Walter A. Lyons ◽  
Steven A. Cummer
Keyword(s):  
United States ◽  
Atlantic Ocean ◽  
Great Plains ◽  
Southeastern United States ◽  
Northern Great Plains ◽  
Total Charge ◽  
Central Plains ◽  
Convective Systems ◽  
Seasonal And Diurnal Variations ◽  
Mesoscale Convective

Abstract The use of both total charge moment change (CMC) and impulse charge moment change (iCMC) magnitudes to assess the potential of a cloud-to-ground (CG) lightning stroke to induce a mesospheric sprite has been well described in the literature, particularly on a case study basis. In this climatological study, large iCMC discharges for thresholds of >100 and >300 C km in both positive and negative polarities are analyzed on a seasonal basis. Also presented are local solar time diurnal distributions in eight different regions covering the lower 48 states as well as the adjacent Atlantic Ocean, including the Gulf Stream. The seasonal maps show the predisposition of large positive iCMCs to dominate across the northern Great Plains, with large negative iCMCs favored in the southeastern United States year-round. During summer, the highest frequency of large positive iCMCs across the upper Midwest aligns closely with the preferred tracks of nocturnal mesoscale convective systems (MCSs). As iCMC values increase above 300 C km, the maximum shifts eastward of the 100 C km maximum in the central plains. Diurnal distributions in the eight regions support these conclusions, with a nocturnal peak in large iCMC discharges in the northern Great Plains and Great Lakes, an early to midafternoon peak in the Intermountain West and the southeastern United States, and a morning peak in large iCMC discharge activity over the Atlantic Ocean. Large negative iCMCs peak earlier in time than large positive iCMCs, which may be attributed to the growth of large stratiform charge reservoirs following initial convective development.

scholarly journals Observational Analysis of the Predictability of Mesoscale Convective Systems

2007 ◽  
Vol 22 (4) ◽  
pp. 813-838 ◽  
Author(s):  
Israel L. Jirak ◽  
William R. Cotton
Keyword(s):  
United States ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
The United States ◽  
Vertical Wind ◽  
Mesoscale Convective Systems ◽  
Convective Initiation ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract Mesoscale convective systems (MCSs) have a large influence on the weather over the central United States during the warm season by generating essential rainfall and severe weather. To gain insight into the predictability of these systems, the precursor environments of several hundred MCSs across the United States were reviewed during the warm seasons of 1996–98. Surface analyses were used to identify initiating mechanisms for each system, and North American Regional Reanalysis (NARR) data were used to examine the environment prior to MCS development. Similarly, environments unable to support organized convective systems were also investigated for comparison with MCS precursor environments. Significant differences were found between environments that support MCS development and those that do not support convective organization. MCSs were most commonly initiated by frontal boundaries; however, features that enhance convective initiation are often not sufficient for MCS development, as the environment needs also to be supportive for the development and organization of long-lived convective systems. Low-level warm air advection, low-level vertical wind shear, and convective instability were found to be the most important parameters in determining whether concentrated convection would undergo upscale growth into an MCS. Based on these results, an index was developed for use in forecasting MCSs. The MCS index assigns a likelihood of MCS development based on three terms: 700-hPa temperature advection, 0–3-km vertical wind shear, and the lifted index. An evaluation of the MCS index revealed that it exhibits features consistent with common MCS characteristics and is reasonably accurate in forecasting MCSs, especially given that convective initiation has occurred, offering the possibility of usefulness in operational forecasting.

scholarly journals A neural network framework for binary classification of radar detections

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Jabran Akhtar
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
False Alarm ◽  
False Alarm Rate ◽  
High Probability ◽  
Binary Classification ◽  
Guard Cells ◽  
Probability Of Detection ◽  
Constant False Alarm Rate

AbstractA desired objective in radar target detection is to satisfy two very contradictory requirements: offer a high probability of detection with a low false alarm rate. In this paper, we propose the utilization of artificial neural networks for binary classification of targets detected by a depreciated detection process. It is shown that trained neural networks are capable of identifying false detections with considerable accuracy and can to this extent utilize information present in guard cells and Doppler profiles. This allows for a reduction in the false alarm rate with only moderate loss in the probability of detection. With an appropriately designed neural network, an overall improved system performance can be achieved when compared against traditional constant false alarm rate detectors for the specific trained scenarios.

scholarly journals Tornadoes from Squall Lines and Bow Echoes. Part I: Climatological Distribution

2005 ◽  
Vol 20 (1) ◽  
pp. 23-34 ◽  
Author(s):  
Robert J. Trapp ◽  
Sarah A. Tessendorf ◽  
Elaine Savageau Godfrey ◽  
Harold E. Brooks
Keyword(s):  
United States ◽  
Tropical Cyclones ◽  
Early Morning ◽  
Time Of Day ◽  
Primary Objective ◽  
Radar Reflectivity ◽  
Convective Systems ◽  
Late Night ◽  
Squall Lines ◽  
Tornado Event

Abstract The primary objective of this study was to estimate the percentage of U.S. tornadoes that are spawned annually by squall lines and bow echoes, or quasi-linear convective systems (QLCSs). This was achieved by examining radar reflectivity images for every tornado event recorded during 1998–2000 in the contiguous United States. Based on these images, the type of storm associated with each tornado was classified as cell, QLCS, or other. Of the 3828 tornadoes in the database, 79% were produced by cells, 18% were produced by QLCSs, and the remaining 3% were produced by other storm types, primarily rainbands of landfallen tropical cyclones. Geographically, these percentages as well as those based on tornado days exhibited wide variations. For example, 50% of the tornado days in Indiana were associated with QLCSs. In an examination of other tornado attributes, statistically more weak (F1) and fewer strong (F2–F3) tornadoes were associated with QLCSs than with cells. QLCS tornadoes were more probable during the winter months than were cells. And finally, QLCS tornadoes displayed a comparatively higher and statistically significant tendency to occur during the late night/early morning hours. Further analysis revealed a disproportional decrease in F0–F1 events during this time of day, which led the authors to propose that many (perhaps as many as 12% of the total) weak QLCSs tornadoes were not reported.

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