Analysis of the Development of the Intense Warm-Core Mesovortex Associated with the 8 May 2009 Central United States "Super Derecho" Event

During the morning of 8 May 2009, a derecho-producing convective system (DCS) developed over Kansas and proceeded eastward, resulting in widespread wind damage from the Central Plains into the Ohio Valley. As the DCS traversed from Kansas into Missouri, an intense, meso-beta-scale warm-core vortex formed on its northern flank. Previous studies, both in print and in review, have both described the structure of the DCS and assessed the environment in which the DCS and its accompanying warm-core vortex formed. At the last Severe Local Storms conference, utilizing output from a 3 km horizontal grid spacing WRF-ARW numerical simulation that accurately captured the formation and evolution of the DCS, we presented a series of preliminary circulation budget analyses aimed at describing the formation of the intense warm-core line-end vortex. However, it remains unclear as to precisely how the warm-core vortex formed.

In this presentation, we utilize the aforementioned WRF-ARW simulation output to more completely describe the formation of the intense warm-core line-end vortex. Quasi-Lagrangian back trajectory analyses are used to assess how vertical vorticity found in association with convective elements along and ahead of the DCS is generated. In so doing, the contributions of buoyantly-generated and environmental horizontal vorticity to this process, both streamwise and crosswise in nature, are discussed. Correlation coefficients between the vertical vorticity and updraft fields are computed to establish the supercell-like nature of the convective cell at the northern extent of the DCS. Selected budget analyses are presented to elucidate the possible role of vortex merger in the formation of the warm-core line-end vortex. Comparisons will be drawn between the process(es) of vortex formation identified herein and those associated with other convective phenomena on the meso-gamma to the synoptic-scale.