UNIFIED FORECAST SYSTEM : Convective-Allowing Forecast and Data Assimilation System

UNIFIED FORECAST SYSTEM : Convective-Allowing Forecast and Data Assimilation System


1. Preamble

The UFS Short-Range Weather/Convective-Allowing Model (SRW-CAM) Application Team's charge is to create, using the FV3 limited area (FV3-LAM) model, a convective-allowing ensemble-based data assimilation and forecast system for the 0-3 day range. This system will replace the current convection-allowing guidance systems in the NCEP Production Suite (NPS). This development is a collaborative effort between NWS (NCEP/EMC), OAR (NSSL, GSL, GFDL), NCAR, the DTC, and academia. Experience gained from the development of earlier operational and experimental CAM systems such as the GSL’s HRRR/HRRRE, the NAM nests from NCEP/EMC, the NSSL Experimental Warn-on-Forecast System for ensembles (NEWS-e), the NCAR experimental CAM ensemble, and GFDL’s FV3-based CAM efforts, will guide this project as it evolves. The anticipated operational system, the Rapid Refresh Forecast System (RRFS), will be a single-core (FV3) CAM ensemble-based data assimilation and forecast system. The RRFS is planned for operational implementation in FY2023.


2. Background and Development Timeline

As part of its commitment to the implementation of a unified forecast system in NCEP’s Production Suite, NOAA is planning to replace NCEP’s myriad mesoscale and convective-allowing systems with new guidance systems based on the FV3 dynamic core. As of July 2018, the NCEP meso/CAM scale modeling suite currently consists of the following components:

  1. North American Mesoscale (NAM) system: Runs the Non-hydrostatic Multiscale Model on B-Grid (NMMB). The NAM consists of a North American 12-km parent domain run to 3.5 days and 4 non-moving nests run to 2.5 days at 3-km resolution over the CONUS, Alaska, Puerto Rico, and Hawaii. An additional 1.5 km nest is run over a pre-selected part of the CONUS or Alaska to 1.5 days for fire weather support operations. The NAM features an 6-h data assimilation cycle with hourly analysis updates for the 12 km parent domain and the 3 km CONUS/AK nests.
  2. High-Resolution Window (HiResW):  Consists of ~ 3-km runs of the NMMB model and two configurations of the ARW model over the CONUS, Alaska, Hawaii, Puerto Rico, and Guam (single ARW run only). In the spring/summer of 2021, the NMMB model will be replaced by the FV3-LAM. 
  3. High-Resolution Ensemble Forecast (HREF) system: Current/time-lagged HiResW and NAM CONUS nests are used to generate ensemble products. Current version is an 8-member ensemble for CONUS with HiresW and NAM CONUS nest members; HREF for Alaska, Hawaii, and Puerto Rico are a 6-member ensemble with HiResW members only. 
  4. Short-range Ensemble Forecast (SREF) system: Runs at 16 km over North America and currently consists of 26 members (13 NMMB, 13 ARW) with physics/initial condition diversity.
  5. Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR): The RAP and HRRR are run hourly out to 21 hr and 18 hr, respectively. RAP is run at 13-km resolution over North America (identical to the NAM parent domain), while HRRR is run at 3 km over CONUS. With the implementation of RAPv5/HRRRv4 in December 2020, the 00/06/12/18z HRRR cycles run to 48-hr, and the 03/09/15/21z RAP cycles run to 51-h. As part of this upgrade, the CONUS HRRR will begin using a HRRR Data Assimilation System (HRRRDAS), a storm-scale (3km) ensemble data assimilation in which 36 members are integrated for one hour, and ensemble Kalman Filter data assimilation is performed including direct reflectivity assimilation. The ensemble mean then provides the initial conditions for the HRRR spin-up and analysis process. The Alaska HRRR (implemented in 2018) will continue to use initial conditions from the RAP.

NAM development was frozen after the March 2017 upgrade, and RAP/HRRR development with the WRF-ARW model will cease after the RAPv5/HRRRv4 upgrade in 2020. However, operational execution of these modeling and associated DA systems will continue until comparable FV3-based systems are able to give similar performance.

FY2019-FY2020 : HRRR v4 implementation and FV3-LAM development

  • Development of the FV3-based limited-area (FV3-LAM) to bring its capabilities and performance up to that of the current CAM systems
  • Finalize and implement RAPv5/HRRRv4
  • Add the extended HRRR forecasts to HREF, replace NMMB members in HREF with SAR-FV3 members
  • Preliminary ensemble DA testing with FV3-LAM


FY2020-FY2021 : FV3-LAM development/testing for Meso/CAM

  • Finalize porting of HRRR physics into CCPP for use in FV3-LAM
  • Finalize FV3-based RAP
  • Continue evaluation of FV3 SAR against existing systems
  • Continue development and testing of DA capabilities with FV3-LAM
  • Continue evaluation in NOAA testbeds


FY2021-FY2023 : Evolution to a FV3-based single core Rapidly Refreshed Forecast System (RRFS) : FV3 CAM ensemble with DA

  • Ensemble analysis and forecast system development with FV3_LAM and JEDI
  • Development of stochastic physics for single core
  • Continue evaluation in NOAA testbeds
  • Pursuant to favorable evaluation, implement RRFS v1.0 [2023]





3. Ongoing Efforts

EMC : Developed a limited area regional version of the FV3 and adapted the NCEP Unified Post-Processor (UPP) and Grid-scale Interpolation (GSI) analysis for the FV3LAM. Currently running several real-time parallel experiments with the RRFS physics baseline:

  • Test of RRFS prototype : 60-h forecast of a CONUS domain vs the 3 km North American RRFS domain, both using the operational GFS for initial and boundary conditions
  • Data Assimilation tests : Two 3-km CONUS domain runs of a 6-h DA system (coldstarted from the GDAS) with hourly GSI analysis and forecast updates, followed by a 60-h FV3LAM forecast. One of these is a control run while the other run tests changes in the DA system (new observations, GSI or hybrid DA changes)

GSD : Developed RAP-sized FV3 domain and modifying pre-processing to use RAP instead of GFS / FV3GFS input for lateral boundary conditions. Worked with EMC on developing better grid-spacing uniformity for the continental FV3-RAP domain, which is now being applied to all 3 km LAM configurations. 

EMC/GSD/NSSL/Developmental Test Bed Center (DTC) : Developed and released the Short-Range Weather Application Version 1 in March 2021; working on enhancing the FV3-LAM community workflow to incorporate a common Data Assimilation workflow for the RRFS. 


4. Links to Relevant Documents/Web Sites