Documentation of a Rare Tornadic Left-Moving Supercell

Matthew J Bunkers,John W Stoppkotte

doi:10.55599/ejssm.v2i2.7

Matthew J Bunkers, John W Stoppkotte

Open Access

https://doi.org/10.55599/ejssm.v2i2.7

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Abstract

An F1 anticyclonic tornado (i.e., clockwise rotation in the Northern Hemisphere) was produced by an intense left-moving/anticyclonic supercell near Rushville, Nebraska, on 20 June 2006. This is only the fifth formally documented left-moving supercell that produced an anticyclonic tornado. The left-moving supercell exhibited an impressive hook echo, mesoanticyclone, and bounded weak-echo region at the time of tornado occurrence—rivaling those of its right-moving counterparts. Since tornadic left-moving supercells are extremely rare, and thus potentially difficult to recognize, this paper serves to document the radar characteristics and environmental conditions of this event.

Highlights

During the late afternoon and early evening of 20 June 2006, a moderate-lived (3 h; Bunkers et al 2006) left-moving supercell affected northwestern Nebraska with large hail, damaging winds, and an anticyclonic tornado that destroyed one house
Its classiclooking hook echo and bounded weak-echo region (BWER) developed shortly before the anticyclonic F1 tornado touched down just south of Rushville, Nebraska, the most significant damage from this storm was associated with the nontornadic severe weather
The post-tornadic increase of severe weather was associated with BWER collapse and storm acceleration, which may have prevented additional tornadoes from forming—owing to the overwhelming effects of the surface cold pool

Summary

Introduction

During the late afternoon and early evening of 20 June 2006, a moderate-lived (3 h; Bunkers et al 2006) left-moving supercell affected northwestern Nebraska with large hail, damaging winds, and an anticyclonic tornado that destroyed one house. Anticyclonic tornadoes are generally found in, or near, one of three locations of a thunderstorm: (1) the hook echo region of an anticyclonic supercell, as in the present case, (2) an updraft— not necessarily supercellular—that ingests preexisting anticyclonic vorticity associated with wind shears along boundaries, such as gust fronts 1983), or (3) the anticyclonic shear side of a hook echo associated with a right-moving supercell (Fig. 1 ; Fujita 1977; Brown and Knupp 1980; Fujita and Wakimoto 1982). Wakimoto (1983) estimated the ratio of all anticyclonic tornadoes to all cyclonic tornadoes to be 1:700 (or 0.14%). Based on the authors’ operational experience, it is estimated there are 1–5 tornadic left-moving supercells for every 100 left-moving supercells (i.e., on the order of 1%)

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