Environments of Significant Tornadoes Occurring within the Warm Sector versus those Occurring along Surface Baroclinic Boundaries

Jonathan M Garner

doi:10.55599/ejssm.v7i5.41

Abstract

Archived, hourly-analysis proximity soundings from the operational Rapid Update Cycle (RUC) model are used to examine the vertical wind profiles and thermodynamic parameter space associated with significant tornadoes (rated F2+/EF2+) occurring in the warm sector (33 events) of synoptic cyclones, as well as those occurring along surface baroclinic boundaries (52 events), during the period 1999-2010 over the central and eastern United States. These tornadoes were associated with either the warm sector or a surface baroclinic boundary through the use of subjective surface analyses, supplemented by visible satellite and WSR-88D imagery. A key finding is that measures of ground-relative wind speed, storm-relative helicity, and bulk wind difference are much stronger for warm-sector significant tornado events. In contrast, thermodynamic parameters did not distinguish between the two regimes. Among all of the parameters examined, the observed and predicted speed of the parent supercell showed the most substantial differences between warm-sector and boundary significant tornado environments.

Highlights

IntroductionThe association between low-level baroclinic boundaries and significant tornadoes has received substantial attention during the last few decades
A preliminary investigation by Maddox et al (1980) attributed this association to the enhanced moisture convergence and cyclonic vertical vorticity that reside along a boundary as low-level winds veer from easterly on the cool side to south-southwesterly on the warm side
A database of 79 Rapid Update Cycle (RUC) model analysis proximity soundings developed by T03 and Thompson et al (2007; hereafter T07), spanning from April 1999 to June 2001, and January 2003 through March 2005, was used to examine the environments associated with significant tornadoes occurring in the warm sector and those interacting with surface baroclinic boundaries

Summary

Introduction

The association between low-level baroclinic boundaries and significant tornadoes has received substantial attention during the last few decades. A preliminary investigation by Maddox et al (1980) attributed this association to the enhanced moisture convergence and cyclonic vertical vorticity that reside along a boundary as low-level winds veer from easterly on the cool side to south-southwesterly on the warm side. Whereas Maddox et al (1980) proposed that vertical vorticity was Despite the strong association between significant-tornadoes and low-level boundaries, many cases of warm sector significant tornado outbreaks occur in the absence of boundaries (and attendant interactions) detectable with standard observation networks.

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