DGEX User’s Guide
IFPS Science Steering Team
Summary: “DGEX”
is an acronym for the Downscaled GFS with Eta Extension. DGEX
has been developed as an interim solution to providing high-resolution –
horizontally and vertically – forecast guidance for populating the digital
forecast database at extended forecast projections. It is produced by running the full 12-km, 60
level, Eta model from forecast hour 78 to forecast hour 192 using lateral boundary
conditions (LBC) from the previous cycle of the GFS. These LBC’s are applied at every 3 hours
between 78 and 174 hr, and every 6 hours between 174 and 192 hrs.
Although the process is started at 78 hrs to allow adjustment to the smaller
grid, the first time step disseminated to the field is 90 hrs. DGEX is available on AWIPS beginning with
OB3.3.
DGEX is not intended to be a
plug and play solution. Users still need to critique it like any other model
and treat it as additional guidance. However,
keep in mind that DGEX provides a dynamically downscaled solution that is ideally
more realistic in character than the much coarser GFS. It offers forecasters the opportunity to
populate their digital forecast grids with a more detailed model first guess
than is available with the operational GFS.
CONUS Data Description: A DGEX
parameter list and model domain is provided in the Appendix. Data are available in 6 hr time steps between
90 and 192 hrs. Model run times are at 06Z (using 00Z GFS for BC) and 18Z
(using 12Z GFS for LBC).
Process to Use DGEX in IFPS/GFE: Several
simple steps are needed to use DGEX in the GFE.
Since the DGEX SmartInit is not scheduled to be part of the GFE baseline
until IFPS17, you should copy over the “DGEX_SmartInit.tgz” file and associated
documentation from the Smart Tool Repository. Follow the instructions provided in the
documentation to install and configure the GFE for DGEX use. The documentation includes a detailed
description of the SmartInits used for DGEX.
More Information: A central collection of DGEX
documents is available at the ISST DGEX
web site: http:// www.nws.noaa.gov/ost/ifps_sst/DGEX.html. Supporting DGEX VISITview session documents
are at http://www.cira.colostate.edu/ramm/visit/dgex.html.
Appendix
DGEX Parameter Description
1. * and bolded parameters indicate field is smoothed
for display (NOTE: no smoothing is performed in GFE)
2. Parameter Set: Some parameters are defined at
multiple levels (or altitudes). Various combinations of levels are listed
in items 3a through 3f, below.
o Pressure at surface
o Total Instantaneous Cloud Cover
o Pressure at MSL (Eta & Normal/NCEP Reduction)*
o Temperature (10 levels, 3a, 3c & 3d,
below)
o Relative Humidity (10 levels, 3a, 3c & 3d,
below)
o Maximum Temperature at 2 meter (from ICWF)
o Minimum Temperature at 2 meter (from ICWF)
o Geopotential. Height (5 levels: 3d, 3e & 3f,
below)
o Vertical Velocity (700 mb, in Pa/sec)*
o u, v-wind (11 levels, 3b, 3c, 3d & 3e, below)
o Surface Lifted Index*
o Total Accum. Precipitation at Surface (6-hr
accumulation)
o Terrain Height (Initial 90hr Time Step Only)
3. Levels (Specified within parameter set above):
a. 2 meters Above Ground Level
b. 10 meters Above Ground Level
c. 0-30mb, 30-60mb, 60-90mb, 90-120mb,
120-150mb, and 150-180mb Above Ground Level
d. 850mb, 700mb and 500mb
e. 250mb
f. 1000mb
4. Data are available at 90, 96, 102, 108, 114, 120,
126, 132, 138, 144, 150, 156, 162, 168, 174, 180, 186, and 192 hr.
Figure 1 – DGEX domains for CONUS and