The utility of total lightning trends in diagnosing single-cell thunderstorm severity: Examples from the central Appalachians region

Abstract

: The utility of total lightning trends in diagnosing single-cell thunderstorm severity: Examples from the central Appalachians region. J. Operational Meteor., 3 (8) ABSTRACTThe performance of a total lightning jump algorithm for guiding severe thunderstorm warnings within a weakly sheared environment was investigated using data from the Earth Networks Total Lightning Network. Total lightning observations from two summers for a study domain within the central Appalachian Mountains region were clustered into likely thunderstorms using single-linkage clustering. The spatial and temporal characteristics of each flash cluster were evaluated and used to assign a "storm index" (SI) score to each cluster. Small, short-lived, slow-moving, circular clusters-consistent with single-cell thunderstormswere given large SI scores, and large, long-lived, fast-moving, linear clusters-inconsistent with the single-cell mode-received smaller SI scores. Statistical testing revealed that days with a simple majority of lightningdefined (LD) single-cell storms possessed significantly weaker 0-6-km wind shear than days with a majority of non-single-cell storms. After classifying 470 clusters as either LD single-cell or multicell/supercell, the 2σ lightning jump algorithm was applied to the flashes associated with each cluster. Total lightning jumps identified by the algorithm were aligned with severe weather report data to evaluate the accuracy of the algorithm. Although probability of detection values for both categories compared well to previous studies, false alarm rates were significantly larger than previously documented. The algorithm performed unsatisfactorily among the LD single-cell and multicell/supercell storms studied, and its performance deteriorated further when applied to a subset of storms most clearly defined as single-cell. However, severe LD storms demonstrated greater flash rates, a promising characteristic for future lightning-based warning tools.

The Emergence of Lightning in Severe Thunderstorm Prediction and the Possible Contributions from Spatial Science

“…While the 2σ algorithm configuration failed to deliver an operationally acceptable level of accuracy within the work of Miller et al (2015b), they did find statistically significant differences in total f lash rate and total DFRDT between severe and non-severe storms. This result corroborates themes of previous studies, indicating that total lightning behavior likely can be utilized to help inform forecasters of imminent severe weather associated with pulse-type storms.…”

“…The 2σ LJA has become the preference of researchers (Chronis et al ; Miller et al ; Rudlosky & Fuelberg ; Schultz , 2014a, ). Under this configuration, the algorithm is triggered by establishing an average total flash rate [flashes per minute (fpm)] and then computing the time rate of change of the average total flash rate (DFRDT; flashes per minute squared).…”

“…A recent study presents a case for caution against applying the 2σ algorithm in all situations. Miller et al () evaluated the performance of the 2σ LJA on 470 storms within the central Appalachian Mountains region of the eastern USA. Storms were segregated by the type of environment – environments conducive to single‐cell storms and more dynamic environments supportive of multicell and supercell storms.…”

“…More advanced efforts have sought to include the separation in time to group flashes into CG (Tuomi & Larjavaara ; Woolford & Braun ; Strauss et al ) and total lightning (Betz et al ) flash cells. Recently, Miller et al () employed historical total lightning data in a forecaster‐informed spatiotemporal clustering approach to identify individual storm cells for use in their LJA validation study (Miller et al ). An inherent difficulty with any historical total lightning‐based storm identification is the large volume of lightning flash data, especially when considering total lightning.…”

“…A recent study presents a case for caution against applying the 2σ algorithm in all situations. Miller et al (2015b) evaluated the performance of the 2σ LJA on 470 storms within the central Fig. 4.…”