Storm-scale Ensemble Probabilistic Forecasts of the 22nd May 2011 Joplin Tornadic Supercell Storm

The NOAA's Warn-on-Forecast (WoF) project is developing numerical weather prediction systems for very short-term O(1 h) storm-scale ensemble probabilistic forecasts, to provide guidance to hazardous convective weather warning operations. As part of the WoF project, retrospective ensemble forecasts of the violent and deadly 22nd May 2011 Joplin, Missouri (MO) tornadic supercell event are produced using the WRF-ARW model and DART data assimilation software. Doppler velocity and reflectivity observations from five WSR-88D radars are assimilated into a relatively coarse 3-km horizontal grid spacing storm-scale ensemble. The probabilistic forecasts from the 3-km ensemble show high probabilities of low-level rotation corresponding roughly to the path of the observed low-level mesocyclone in the Joplin storm. To evaluate the impact of a finer resolution model grid, which could potentially represent fine-scale features better such as the storm mergers and variability in mesocyclone strength during the period of interest, additional data assimilation and forecast experiments will be conducted at 1-km model-grid spacing, and a series of ensemble forecasts will be launched from the analyses during the 1 h period preceding the tornadogenesis. At the conference, the ability of these 1-km ensemble forecasts at lead times up to 1 h to reproduce the low-level rotational characteristics of the tornadic supercell storm will be compared to that from the 3-km horizontal grid spacing ensemble forecasts.