To investigate the practical and intrinsic predictability of the 8 May 2009 “Super Derecho” MCS and its warm-core mesoscale vortex, a fifty-member Ensemble Kalman filter (EnKF)-based cycled data assimilation and numerical simulation forecast system is developed. The EnKF-based data assimilation system utilized within this study is that implemented within the Data Assimilation Research Testbed (DART). Cycling of the data assimilation system is conducted using version 3.7 of the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) numerical forecast model. Technical details of the cycled data assimilation and numerical simulation forecast system closely resemble those of Romine et al. (2013, 2014, both Mon. Wea. Rev.) and Schwartz et al. (2015, Wea. Forecasting). Cycled data assimilation commences at 1200 UTC 2 May 2009 and proceeds every six hours until 1200 UTC 7 May 2009, at which time numerical simulations (extending out 36 h at a horizontal grid spacing of 3 km) are launched. Results from the cycled data assimilation and numerical simulation system will be presented. Particular emphasis will be given to quantification of the ensemble's ability to accurately forecast the development and structure of the “Super Derecho” event, including its accompanying warm-core mesoscale vortex, and evaluation of the effects of initial condition uncertainty upon forecast variability and skill.