Near-Storm Environments of Outbreak and Isolated Tornadoes

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.

Quantifying relationships between environmental factors and power dissipation on the most prolific days in the largest tornado “outbreaks”

“…There is also a tendency for days having the most tornadoes to occur farther to the east. The overall pattern of cluster centroids is similar to the pattern shown inAnderson-Frey et al (2018), who used kernel density to define the clusters.…”

“…The American Meteorological Society formally defines a tornado outbreak as "multiple tornado occurrences associated with a particular synoptic-scale system" (American Meteorological Society, 2018). Less formally it is understood that an outbreak is a cluster of several to dozens of tornadoes that occur within a relatively short time scale and over a limited geographic region (Elsner et al, 2015;Malamud et al, 2016;Tippett et al, 2016;Anderson-Frey et al, 2018). We focus on tornado clusters in this work rather than on individual tornadoes because the larger spatial and temporal extents of clusters better match the scale represented by the environmental data.…”

“…James B. Elsner wrote some of the code and edited the paper. storm-relative helicity) important to the development of tornadoes (Brooks et al, 1994;Brown, 2002;Craven et al, 2002;Doswell III and Evans, 2003;Jackson and Brown, 2009;Gensini and Ashley, 2011;Dean and Schneider, 2012;Cheng et al, 2016;Anderson-Frey et al, 2018). Missing from these studies is a quantification of the relationships between environmental factors and collective tornado activity.…”

A Challenging Tornado Forecast in Slovakia

“…Because of the distances between individual weather stations to the tornado site, and the fact that they represent the wind field under the influence of friction, a reconstructed wind profile offers only a rough estimation of reality. Nevertheless, comparing the forecast hodograph using OPM to the reconstructed hodograph clearly showed that the model underestimated the lower tropospheric wind shear ( Figure 10 [5,46,48] and Europe [16,17,49]. "Kink" in the lowest 500 m of the reconstructed hodograph also suggested almost purely streamwise vorticity in the inflow to the storm in that layer, a condition that was deemed favorable for tornadogenesis by Coffer et al (2017) [20].…”

“…Shear in the 0-3 km layer was also substantially stronger in the reconstructed wind profile, with SRH reaching 285 m 2 s -2 , in contrast to 110 m 2 s -2 based on the forecast profile. Such values have been associated with tornadoes both in the U.S. [5,46,48] and Europe [16,17,49]. "Kink" in the lowest 500 m of the reconstructed hodograph also suggested almost purely streamwise vorticity in the inflow to the storm in that layer, a condition that was deemed favorable for VAD measurements were available from the Kojšovská hol'a radar site, starting at an altitude of 1.2 km a.s.l.…”