Using MYRORSS Azimuthal Shear Analyses and Observation-Driven Simulations to Explore the Predictability of Supercell Evolution on 27—28 April 2011

The prolific 27–28 April 2011 tornado outbreak produced multiple rounds of tornadic supercells in four spatiotemporal regions. All of these regions exhibited extremely favorable environments, with small differences in thermodynamic and kinematic profiles and varying proximities to boundaries. This study uses multiple radar-based and environmental observations to inform high-resolution, 25-member numerical ensembles of five select supercells that formed in these regions. Storm Prediction Center SFCOA profiles (RUC profiles blended with surface observations) are used in a base-state substitution technique to continuously nudge the simulated environments towards observations. A more gradual tendency nudging convection initiation technique is used to attempt to capture the mesocyclone development noted in MRMS-based azimuthal shear analyses. Individual ensemble members vary in the magnitude and duration of tendency nudging. This study provides insight into the effects of small changes in tendency nudging on simulated storms across different, albeit all extreme, environments. The resulting simulations are compared to AzShear data from the MYRORSS dataset to judge the performance of our combined tendency nudging and base-state substitution approach, evaluate how much of the observed storm evolutions may have been dependent on the background mesoscale environment, and assess the resulting predictability of the observed storm evolutions.