Description of the NSSL Experimental Warn-on-Forecast System for ensembles

The production of accurate, short-range (0-1 h) probabilistic forecasts of hazards associated with severe convective storms (i.e. tornadoes, damaging winds, and flooding) is one of the primary goals of the NOAA Warn-on-Forecast (WoF) research program. As part of the ongoing work involving ensemble-based numerical weather prediction associated with this program, the NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e) was developed, and will be tested in quasi-realtime during the NOAA Hazardous Weather Testbed (HWT) 2015 Spring Experiment. This presentation will include a description of the NEWS-e and a demonstration of how analyses/forecasts from the NEWS-e were examined by HWT participants.

The NEWS-e employs the Weather Research and Forecasting (WRF) model in a one-way nested framework with a 3-km inner domain nested within a 15-km parent, CONUS-sized domain. Ensemble members from the 1800 UTC forecast cycle of the Global Ensemble Forecast System (GEFS) are coupled with the 1800 UTC North American (NAM) model to provide the initial and lateral boundary conditions. WRF model “multiphysics” are employed across the NEWS-e members to address deficiencies in the model physics and increase spread within the ensemble. An ensemble adjustment Kalman filter (EAKF) encoded within the Data Assimilation Research Testbed (DART) software package is used to assimilate routinely available “conventional” (i.e. METAR, rawinsonde) observations of altimeter setting, temperature, dewpoint, and horizontal wind components at hourly intervals on both domains simultaneously until just prior to convective initiation. Storm-scale data assimilation of radar and high-resolution satellite observations using the DART-EAKF then begins on the 3-km inner domain only for the remainder of the convective episode, with 90-min ensemble forecasts launched at half-hourly intervals within this procedure (as described in a companion abstract by D. Wheatley).

Fields such as 2-m dewpoint, CAPE, updraft helicity, and vertical vorticity will be output by the NEWS-e throughout the convective episode and visualized through the Probabilistic Hazard Information (PHI) web-based tool. Forecasters and visiting scientists in attendance will examine the efficacy of the quasi-realtime NEWS-e output and provide feedback on its performance. Examples of PHI-based NEWS-e output and participant feedback will conclude the presentation.