A WRF-DART Study of the Nontornadic and Tornadic Supercells Intercepted by VORTEX2 on 10 June 2010

On 10 June 2010, the VORTEX2 armada collected a rare set of observations of a nontornadic and a tornadic supercell evolving in close proximity to each other near Last Chance, CO.  An observational study of why one supercell produced no tornadoes while the other produced at least two suggested that a combination of an evolving storm environment and differing impacts of a storm merger on both supercells likely played a significant role.  Over time, the storm environment experienced large thermodynamic changes and increases in storm-relative helicity, leading to conditions much more favorable for tornadogenesis.  A new storm developed between the supercells and merged with both, likely leading to the demise of the nontornadic supercell before it was able to experience these enhanced environmental conditions.  After the merger, the tornadic supercell proceeded to generate two tornadoes.
Preliminary simulations using WRF-DART are conducted to further investigate:  (1) the impacts of the merger (through changing baroclinicity and/or convergence) and the evolving storm environment on the tornadic supercell's tornado production, (2) how the merger killed the nontornadic supercell, and (3) if the nontornadic supercell would have produced tornadoes had the merger not occurred.  We initialize WRF-DART with 50 ensemble members the day of (using GFS data) and assimilate conventional observations (metar, radiosonde, aircraft, and profiler) hourly onto a 3-km grid using EnKF techniques.  Closer to the time of storm initiation, we assimilate KFTG-88D radar data (radial velocity and reflectivity) onto a nested 500-m grid, and, after initiation, mobile radar, mesonet, and sounding data from VORTEX2 as well.  We explore the ensemble results of these simulations to gain better insight into the evolution of the storms and the production of the tornadoes.