Exploring the Optimal Configuration of the High Resolution Ensemble Forecast System

The High Resolution Ensemble Forecast system version 2 (HREFv2) was implemented in the National Weather Service (NWS) on 1 November 2017 as an operational version of the Storm Prediction Center (SPC) Storm-Scale Ensemble of Opportunity (SSEO). Since 2011, the SSEO showed utility in SPC operations on a year-round basis and generally performed as good as or better than formally designed convection-allowing model (CAM) ensembles during past Spring Forecasting Experiments (SFEs) in the NOAA Hazardous Weather Testbed (HWT) for providing severe weather guidance. During the 2017 HWT SFE, the HREFv2 performed similarly to the SSEO, including higher subjective ratings and slightly better objective verification metrics than the other CAM ensembles examined. Thus, the operational HREFv2 serves as a meaningful baseline against which experimental and future CAM ensembles should be compared for consideration of operational implementation.

With the 2018 warm season operational implementation of the extended High Resolution Rapid Refresh (HRRR) runs at 0000, 0600, 1200, and 1800 UTC to 36 hours, there is an opportunity to test the HRRR model as an additional member of the HREF. Multiple experimental configurations of the HREF will be tested and evaluated during the 2018 HWT SFE to help inform how to best configure the next operational version of HREF (i.e., v2.1). The configurations examined will include the current operational HREFv2, a version that adds extended HRRR runs to the HREFv2, and a version that only examines the current CAM runs at 0000 and 1200 UTC (i.e., no time-lagged members). The results of the subjective and objective evaluation of these different experimental HREF configurations during the 2018 HWT SFE will be presented.