An Investigation of the Conditional Practical Predictability of the 31 May 2013 Heavy-Rain–Producing Mesoscale Convective System

During the local evening hours on 31 May 2013, a supercell thunderstorm responsible for a deadly tornado in El Reno, OK grew upscale into an intense mesoscale convective system (MCS). This MCS, which exhibited both quasi-stationary and backbuilding characteristics, resulted in significant flooding and multiple fatalities in the northwestern Oklahoma City, OK metropolitan area. Schumacher (2015, Mon. Wea. Rev.) showed that high-resolution deterministic forecasts of this MCS had large sensitivity to convection initiation (CI) associated with variations in horizontal grid spacing and planetary boundary layer parameterization.

MCSs can significantly impact society with heavy rain and damaging winds, yet the extent to which they are predictable is somewhat limited. However, most MCS predictability research either prescribes CI or implicitly assumes that it will occur, likely overstating MCS predictability because CI is associated with its own limited predictability. Thus, this research seeks to quantify MCS predictability when CI is not prescribed or assumed for the 31 May 2013 central Oklahoma MCS. Whereas Schumacher (2015) documented sensitivity to model configuration for this case, here we seek to document sensitivity to initial and lateral boundary condition uncertainty.

A fifty-member ensemble adjustment Kalman filter-based cycled data assimilation and numerical simulation forecast system is used to facilitate this study. The lanai release of the Data Assimilation Research Testbed (DART) software and version 3.9 of the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) numerical forecast model are used for data assimilation and cycling, respectively. Cycled data assimilation begins at 1200 UTC 26 May 2013, with 6 h cycling continuing thereafter until 1200 UTC 31 May 2013. The resulting ensemble initial conditions are used to initialize two-way-nested 15-/3-km numerical simulations that extend forward 36 h to 0000 UTC 2 June 2013. Results are presented with a particular focus on quantifying the practical predictability of CI preceding the MCS, heavy precipitation associated with the MCS, and the MCS’s quasi-stationary and backbuilding characteristics.