Regional and Mesoscale Meteorology Branch

Downscaled GFS with Eta Extension (DGEX): Its uses and limitations

Introduction

The National Weather Service requires forecasters to create digital forecast products for the National Digital Forecast Database (NDFD) on 5 km (some offices use 2.5 km) grids out to seven days. The model guidance available as one source of first guess inputs includes Eta model 12-km grids out to 84 hours and 80-km and coarser, GFS grids for the remainder of the forecast period. Therefore, the Eta model is now being used to dynamically downscale the GFS solution by extending the run out to 8 days using smaller domains with boundary conditions supplied by the GFS, hence the name Downscaled GFS with Eta Extension (DGEX). The hope is that the 12-km grids will allow forecasters to spend less time tweaking the extended range forecast products while producing grids that are consistent with the topography and weather features at the high resolution of NDFD.

This training provides additional background on the DGEX including domains and available fields on AWIPS, a comprehensive performance assessment, reviews of case examples illustrating key points in how to most effectively utilize it, and discussion of the tension between forecast detail and forecast accuracy inherent in the high-resolution digital forecast process as it is played out through use of the DGEX.

Training Session Options

NOAA/NWS students – to begin the training, use the web-based video, YouTube video, or audio playback options below (if present for this session). Certificates of completion for NOAA/NWS employees can be obtained by accessing the session via the Commerce Learn Center

1. Audio playback (recommended for low-bandwidth users) – This is an audio playback version in the form of a downloadable VISITview and can be taken at anytime.

   Create a directory to download the audio playback file (59 MB) from the following link: http://rammb.cira.colostate.edu/training/visit/training_sessions/downscaled_gfs_with_eta_extension_dgex/downscaled_gfs_with_eta_extension_dgex_audio.exe

   After extracting the files into that directory click on either the visitplay.bat or visitauto.bat file to start the lesson. If both files are present, use visitauto.bat

2. VISITview playback without Audio – You may step through the VISITview file on your own to view the presentation. If talking points are available, you may use these in tandem with going through the slides.

   Create a directory to download the playback file from the following site: http://rammb.cira.colostate.edu/training/visit/training_sessions/downscaled_gfs_with_eta_extension_dgex/downscaled_gfs_with_eta_extension_dgex.exe

   After extracting the files into that directory click on the visitlocal.bat file to start the lesson. Advance slides on your own using the navigation controls (i.e., the Next button will advance to the next slide)

References/Additional Links

• Talking points are available for this lesson and may be printed out to easily review the session in detail at any time.
• Operational Models Matrix: Characteristics of Operational NWP Models
• Application of NWP Concepts