Advancements of the FV3 Stand-Alone Regional Model

Under NOAA’s Strategic Implementation Plan (SIP) for the Unified Forecast System (UFS), the National Centers for Environmental Prediction’s modeling suite will evolve towards a series of UFS applications that will function on temporal scales from short-term weather prediction on the order of hours to days through the medium-range weekly weather to sub-seasonal/seasonal (S2S) forecasts on the order of months. The UFS applications will also function across spatial scales from regional high-resolution convection-allowing model (CAM) forecasts to the mesoscale across the globe. NCEP adopted the Finite Volume-3 (FV3) dynamic core for the UFS, however, current and foreseeable-future supercomputing capacity is insufficient for running a frequently-updating uniform 1-3 km resolution global model that meets the stakeholder requirements for convective-scale weather forecasts. Therefore, the SIP CAM annex provides the transitional steps toward development of a stand-alone regional (SAR) FV3 and movable nest capability to address the immediate needs for regional severe weather and global tropical cyclone (TC) forecast and research applications within the unified modeling system (i.e., FV3GFS). The Bipartisan Budget Act of 2018 includes the Disaster Related Appropriations Supplemental, in response to hurricanes Harvey, Irma, and Maria of 2017. Supported by this funding, NOAA is accelerating its UFS model development efforts. This presentation will describe a project including the establishment of a stand-alone regional (SAR) convection allowing model (CAM) based on the FV3 core and several related efforts. A second effort in this project is development of a telescopic nesting technique within the SAR FV3 that can be used for a wider range of severe weather applications, including creation of fire weather nests within the SAR model. A third effort will further develop the SAR CAM modeling system to incorporate Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) hourly data assimilation and physics from the mesoscale (12-km) to CAM (3-km) and even higher (750 m) resolution tests. A fourth effort will develop the SAR CAM model for the Warn-On-Forecast application including specific threats from landfalling hurricanes and severe convective storms. The FV3-SAR CAM application, known as the Rapid-Refresh Forecast System (RRFS), is expected to replace the North American Model (NAM) parent and nest along with other Weather Research Forecast (WRF)-based models including the Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) as well as the High-Resolution Ensemble Forecast System (HREF). The presentation will discuss these project efforts including progress to date, existing challenges and estimates for a timeline of the evolution towards the RRFS from the existing regional suite of models.