Application of the High-Resolution Rapid Refresh (HRRR) to the Bay Area Advanced Quantitative Precipitation Information Project

The Bay Area Flood Protection Association has just recently begun funding the Physical Sciences Division and Global Systems Division (GSD) of NOAA’s Earth System Research Lab (NOAA-ESRL), as well as the NOAA Cooperative Institute for Research in the Atmosphere (CIRA), to design and build a specialized nowcast / forecast system for the 9 California counties bordering the San Francisco Bay. The principal purpose of this system, known as Advanced Quantitative Precipitation Information, is to provide improved quantitative estimates and forecasts of runoff into San Francisco Bay on small spatial scales and on time scales of minutes to 10 days. As such there will be both a nowcast and a forecast component, both of which will be integrated into NWS operations at the Monterey CA NWS forecast office. The purpose of this presentation is to outline the ESRL-GSD participation and goals for this project, and some of the hydrological and meteorological challenges it represents.

GSD will use the 3-km high-resolution rapid refresh (HRRR) model to provide very short-term forecasts for this project. GSD will build upon its experience and expertise in high-resolution frequently updating assimilation used in the 13-km rapid-refresh (RAP) and HRRR models to incorporate data from C- and X-band radars that will be deployed in the Bay Area by CIRA as part of the project, and to exploit the rapid-scan capabilities onboard GOES-16 to augment initialization of the HRRR, all with the goal of determining whether these additional data sources can be used effectively to improve HRRR very short term quantitative precipitation forecasting. Further, we plan to address forecast uncertainty by use of a HRRR ensemble forecast system under development at GSD. The value added of a high resolution (750m horizontal grid spacing) nest within the HRRR covering the Bay Area and offshore to better capture the impact of the complex topography of this region on precipitation distributions will be examined for selected cases.