EOMF-17. AQPI: Evaluating California Atmospheric River Events with the HRRR Ensemble

Abstract
Improved forecasts of Atmospheric River (AR) events, which provide nearly half of California's annual precipitation, can reduce impacts to lives, property, and water storage. We evaluate forecasts of five AR events that occurred in Feb-Mar 2019 using the High Resolution Rapid Refresh Ensemble (HRRRE). Model ensembles such as the HRRRE, which is based on HRRR version 4 and contains nine ensemble members, can provide probabilistic forecasts and insights into forecast uncertainty. We compare quantitative precipitation forecasts (QPF) to widely-used quantitative precipitation estimation (QPE) products such as the Stage IV analysis and the Mesonet gauge network. We calculate ensemble mean and spread, quantify ensemble forecast performance at varying lead times, and explore possible causes of errors of individual ensemble members. These results can provide understanding of the usefulness of the HRRRE for forecasting AR events along the West Coast, and guide future model development.