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Numerical Weather Prediction (NWP) Professional Development Series


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

Stephen Jascourt (UCAR / COMET)

1) 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.

2) Prerequisites

    Familiarity with using the NCEP Eta and GFS models in the forecast process

3) Teletraining Installation Instructions


4) Training Session Options:

    A.) The interactive VISITview training session. (To be used with a VISIT instructor leading the session ). Click here to signup for teletraining. The session will last 90 minutes. This teletraining session uses the VISITview software, where Windows PC (with 128 MB RAM or greater) with an Internet connection is needed.

    B.) Web-based training session - a "stand alone" version viewed via a Web browser, with embedded talking points included. This lesson version may be viewed at any time. These slides are ideal for printing from the web-browser, just print preview first to choose portrait or landscape mode. Best viewed with Internet Explorer or Netscape (prior to version 6).

    C.) Web-based Visitview session (coming soon) - This version uses the VISITview software within a Web browser, may be viewed at any time. It retains all the functionality of the VISITview software which you see in a "live" teletraining session. The talking points are not included in this lesson version, but can be viewed in a separate Web browser (or printed out beforehand).

    D.) local Visitview session - This is the same version of the lesson used in a "live" VISITview teletraining session, but no connection is made to an external VISITview server. You may download the file off this page and go through the lesson on your own in "local mode" by starting the "visitlocal.bat" file. Talking points are not included in this lesson version, but can be viewed in a separate Web browser ( or printed out beforehand).

    E.) Audio playback - This VISITview file contains recorded audio and annotations and can be taken at anytime. Certificates of completion for NOAA employees can be obtained through your Science Operation Officer or training point of contact. For detailed information on how to view the recorded session click here.

    You may either request a DVD (with all VISIT audio playback files) OR download the file (see instructions below):

    Create a directory to download the audio playback file (it is about 51 MB in size) from one of the following sites:

    ftp://rammftp.cira.colostate.edu/bikos/audio/DGEX_audio.exe
    or
    ftp://ftp.ssec.wisc.edu/visit/audio/DGEX_audio.exe

    After extracting the files into that directory click on the visitauto.bat file to start the lesson.

5) References/Additional Links


6) Train the trainer

    Talking points - these may be used by local offices in tandem with the visitview training session (run in local mode - "visitlocal.bat"). The talking points may be printed out to easily review the session in detail at any time. The web page version contains talking points embedded in each slide (useful for printing).

7) Content developed/updated
    2004
8) Information contact