Impact of Assimilating CASA X-Band Radar Data for 24 May 2011 Tornadic Storms Using Various Microphysics Schemes at 1-km Grid Resolution

On 24 May 2011, Western and Central Oklahoma experienced an outbreak of tornadoes, including one rated EF-5 and two rated EF-4. The extensive observation network in this area, including the WSR-88D radars, Collaborative Adaptive Sensing of the Atmosphere (CASA) X-band radars, Oklahoma Mesonet, and National Weather Service (NWS) and Federal Aviation Administration METAR, makes this an ideal case to explore forecast capabilities applicable to the Warn-on-Forecast (WoF) concept and potential impact of X-band radar data. Using these data, the CAPS real-time forecasting system had good success in simulating these storms, but the impact of assimilating CASA radar data on various microphysics schemes' abilities to simulate the storms and their structure was not clear. The aim of this study is to examine the effect of assimilating CASA radar data using five different microphysics parameterization schemes, including the Lin 3-ice microphysics scheme, Weather Research and Forecasting (WRF) single-moment 6-class (WSM6) microphysics scheme, Milbrandt and Yau (MY) single-moment bulk microphysics scheme, MY double-moment bulk microphysics scheme, and MY triple-moment bulk microphysics scheme, on the genesis and evolution of simulated mesocyclones as compared to each other and reality. The verification method used is an object-based technique in which the mesocyclone centers are represented by 1–6-km and 0–1-km updraft helicity fields and are verified against tornado locations determined from National Weather Service damage surveys and low-level radar signature tracks. By determining spatial and temporal errors, this verification technique effectively highlights model successes and failures associated with assimilating CASA radar data using a spectrum of microphysics schemes and helps define expected error bounds when utilizing microphysics diversity for the WoF ensemble concept. Three tornadic supercells of interest from this event are individually investigated using the Advanced Regional Prediction System (ARPS) model developed at the Center for Analysis and Prediction of Storms (CAPS). To emulate a WoF setting, the ARPS forecast model is run out to two hours starting every 30 minutes from 1900 UTC to 2230 UTC. The ARPS model runs are initialized using incremental analysis updating (IAU) with increments added every 20 seconds in a 5-minute window with no cycling. Analysis increments are obtained from the ARPS three-dimensional variational data assimilation (3DVAR) system and ARPS data assimilation system (ADAS) complex cloud analysis. The 1800-UTC 12-km North American Mesoscale (NAM) model is used for the background fields and lateral boundary conditions. Quantitative scores of the forecast mesocyclone positions produced by the various microphysics schemes with and without assimilating CASA radar data are presented and compared.