Help with gdgrib

• To: gembud@xxxxxxxxxxxxxxxx
• Subject: Help with gdgrib
• From: mpborkow@xxxxxxxx
• Date: Thu, 26 Jan 2006 15:21:14 -0500 (EST)

I have a SST file in GEMPAK which I've been trying to convert to GRIB

converting to an LCC projection with custom grid size and spacing.  I
receive an error about the grid not being found in grdnav.tbl, but the
conversion still works.  But when I try to ingest this ino the WRF model,
my SSTs get extremely distorted.  If I convert my GRIB file back to GEMPAK
and plot it, it plots up fine.

I have now found that if I specify an existing grid by setting
CPYFIL=#218, or if I specify dimensions of an existing grid using PROJ,
GRDAREA, and KXKY of a grid that is found in grdnav.tbl, the conversion
performs without error and the WRF model successfully ingests my file
without distortion.  Unfortunately no existing grid has the resolution I
need over a large enough area.

So my question is, when I convert to GRIB using gdgrib using custom grid
dimensions, is there any critical navigation information that gets left
out of the GRIB file?  The way I see it, if the grid I'm interpolating to
does not exist in grdnav.tbl, something gets left out of the GRIB file and
WRF does not know how to successfully navigate my file, and winds up
blindly interpolating my file to my model domain.  Perhaps I am not
setting something properly in gdgrib?  Here is the settings I've been
using for gdgrib:

GDFILE  = overlay.gem
GFUNC   = TMPK
GDATTIM = 20021224/1800:20021225/0000
GLEVEL  = 0
GVCORD  = none

GRDAREA = 15;-115;50;-50
KXKY    = 803;433

Any help would be greatly appreciated!  Thanks!

Matt
Graduate Student
North Carolina State University
Department of Marine, Earth, and Atmospheric Sciences