The Real-time National Severe Storms Laboratory 4-km WRF Model Ensemble

The National Severe Storms Laboratory (NSSL) and Storm Prediction Center (SPC) have been exploring the use of real-time 4-km grid-spacing convection-allowing Weather Research and Forecasting (WRF) model simulations as forecasting tools since the 2004 NOAA/Hazardous Weather Testbed Spring Forecasting Experiment. The results from these initial tests were extremely positive, with forecasters particularly impressed by the ability of the WRF simulations to depict realistic convective-scale storm structures like bow echoes and discrete supercells. In 2006, these successful tests, along with other positive results from convection-allowing modeling experiments at agencies like NCAR and the Center for Analysis and Prediction of Storms (CAPS), motivated NSSL scientists to establish a more permanent experimental modeling framework to provide storm-scale guidance to SPC forecasters and serve as a testing ground for the development of storm-scale model diagnostics. This real-time modeling framework became known as the NSSL-WRF and has been run the last several years using a computing allocation on the Jet HPC cluster (Raytheon/Aspen Systems) in Boulder, CO.

Beginning in 2007, with support from the NOAA Collaborative Science, Technology, and Applied Research (CSTAR) Program, CAPS began providing experimental convection-allowing ensembles for testing during annual NOAA/HWT Spring Forecasting Experiments. Once again, results from these tests were very positive as the ensembles provided much needed additional information on forecast uncertainty, and several new ensemble visualization strategies and forecast diagnostics were developed. Because of the large computational expense required to integrate a convection-allowing ensemble, the year-round NSSL-WRF system has remained deterministic, with the ensemble experiments led by CAPS limited to the 5-week long Spring Forecasting Experiments during May and June. However, very recently (early 2014), NSSL was granted an increase in computing allocation on the Jet HPC cluster, which is being used to run a year-round, real-time, nine-member convection-allowing ensemble. This ensemble, which is known as the NSSL-WRF ensemble uses the NSSL-WRF as a control member (ICs/LBC from the NAM), with the other eight members using NCEP's SREF system for ICs and LBCs. The ensemble system will serve as permanent ensemble framework to provide guidance to SPC forecasters and serve as a testing ground for developing an optimal ensemble configuration and useful storm-scale ensemble diagnostics. The ensemble began running in March 2014 and was tested and evaluated in the 2014 NOAA/HWT Spring Forecasting Experiment. Also, a new public website has been developed for displaying the real-time forecasts. This talk will provide further details on the ensemble configuration, and present initial subjective and objective results obtained during the 2014 NOAA/HWT Spring Forecasting Experiment.