Comparison of the HRRR Time-Lagged Ensemble to Formal CAM Ensembles during the 2018 HWT Spring Forecasting Experiment

Current resource limitations in operational computing at the National Weather Service preclude the running of an hourly convection-allowing model (CAM) ensemble. However, a practical alternative simply involves the post-processing of the High Resolution Rapid Refresh (HRRR) to generate an hourly time-lagged ensemble (HRRR-TLE). While the spread may be limited from the HRRR-TLE, often resulting in an overconfident solution, there is still operational utility in providing hourly updating probabilistic information on the location, timing, and intensity of severe weather potential. During the 2018 HWT SFE, the HRRR-TLE was evaluated and compared to formally designed CAM ensembles in providing guidance to severe-weather forecasters. On many days during the 2018 HWT SFE, the HRRR-TLE provided useful probabilistic severe-weather guidance and, in some cases, outperformed the more advanced CAM ensemble systems. The results of the subjective and objective evaluations of the HRRR-TLE forecasts compared to other CAM ensembles during the 2018 HWT SFE will be presented.