Wednesday, 24 October 2018: 9:45 AM
Pinnacle room (Stoweflake Mountain Resort )
This study documents the kinematic, thermodynamic, and microphysical evolution of the tornadic 13-14 April 2018 Calhoun, LA supercell that produced three EF-1 tornadoes. The study combines airborne and ground-based observations from VORTEX-SE with a diabatic Lagrangian analysis (DLA) retrieval of temperature and water substance storm fields. A unique aspect of the study is the combination of dual P-3 tail Doppler radar (TDR) observations with ground-based radar observations from the S-band University of Louisiana-Monroe (ULM) radar (KULM) to obtain triple-Doppler airflow analyses of the supercell. Another unique aspect of this study is the coordinated P-3/KULM observation of the Calhoun storm spanning 28 consecutive airborne volumes, each of about 4 min in length, during the period 2309 UTC 13 April through 0120 UTC 14 April. Multiple analyses are obtained before, during, and after each of the three tornadoes during the period 2309-0010 UTC, including 5 consecutive volumes spanning about 20 min prior to the first tornadogenesis event. The DLA is facilitated via unique P-3 airborne Compact Raman Lidar (CRL) profiles of the supercell's inflow boundary layer via our collaboration with the University of Wyoming, combined with conventional, time-spaced ULM balloon soundings.
A preliminary 3-D pseudo-dual-Doppler (dual-TDR) analysis on a 250 meter grid at the end of the first tornado around 2338 UTC reveals an intense low-level tornado-cyclonic circulation containing vertical vorticity values of up to 70 x 10-3 s-1 that is virtually coincident with the NWS-surveyed EF-1 tornadic damage path. An implied moderate-evolution supercell morphology around 2338 UTC is hypothesized to be consistent with the growing ~ 6-km deep, intensely forced tornadic cell in combination with several deeper, more elevated cells downstream. We will present a detailed summary of the triple-Doppler radar-derived storm morphology at the conference, with particular emphasis on evolution before, during, and after tornadogenesis. We will also briefly summarize the retrieved storm-scale thermodynamic and microphysical structure of the storm's main updraft, forward and rear-flank downdrafts, and the surface-based cold pool relative to tornadogenesis.
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