[gembud] NARR conversion to height coordinates?


I'm trying to convert NARR gem files from pressure to height (agl)
coordinates using GDVINT. I've tried various combinations for VCOORD
but I always receive the same error about "required surface elevation is
absent". When I downloaded the grib files, I selected all variables.
Here is some sample output:

 GDFILE    Grid file                         20100128_1800.gem
 GDOUTF    Output grid file                  20100128_1800z.gem
 GDATTIM   Grid date/time                    f00
 GVCORD    Grid vertical coordinate          pres/zagl
 GLEVEL    Grid level                        500-10000-500
 MAXGRD    Maximum number of grids           999
 GAREA     Graphics area                     grid
 VCOORD    Vertical coordinate type          pres;none
 PRES         found.
 TMPK         found.
 HGHT         found.
 SPFH         found.
 OMEG         found.
 UWND         found.
 VWND         found.
 TKE          found.
 CLWMR        found.
 ICMR         found.
 MCONV        found.
 LFTX         found.
* [GDVINT 4]  Warning--no surface elevation grid exists.
 [GDVINT -7]  Required surface elevation is absent.
Does anyone have any experience converting NARR to height AGL coordinates?
Thanks in advance.

Peter C. Banacos, Lead Forecaster
NOAA/National Weather Service
WFO Burlington, VT
E-mail: peter.banacos@xxxxxxxx
Phone: (802) 862-2475