Model | Coverage | Initialized | Interval | Duration | Directory | Filenames |
---|---|---|---|---|---|---|
ETA | N. America | 00Z, 06Z, 12Z, 18Z | 6 hrs | 48 hrs | pub/data/grib/eta/ |
eta_yymmdd_##_** |
AVN | Global | 00Z, 06Z, 12Z, 18Z | 6 hrs | 4 days | pub/data/grib/avn/ |
avn_yymmdd_##_** |
MRF | Global | 00Z | 12 hrs | 16 days | pub/data/grib/mrf/ |
mrf_yymmdd_00_** |
The forecasts are available for downloading between 2 and 12 hours after the initialization time. Be sure to log in as anonymous and set the filetype to binary. The sizes of the individual data files range from about 3 to 13+ MB. You may want to be judicious in your selections, e.g. grabbing only every 12 hours of the AVN forecasts instead of every 6.
1. The GrADS Control File
Below are the links to download sample control files for each of the major forecast models:
These control files may be copied and reused for any new forecast data
provided you modify the tdef
line which specifies the
start time of the forecast. These samples also assume that the
data and map files are in the same directory as the control file. If
they are in different directories, you must provide the full path in
the dset
and index
lines of the control
file.
N.B.: The resolution of the MRF data decreases from 1 degree to 2.5
degrees after 7 days. Thus, 2 control files are required, one for each
resolution. However, the time ranges in the tdef
statements in
both control files are the same, so the user must keep track of the
time and invoke the right control file accordingly. Plotting a
variable at a particular time from the wrong file will result in the
error message, "entire grid undefined".
2. The GRIB Map File
Each time you download new forecast data, you must generate a map file
before you can plot anything with GrADS. The map file is generated
using the gribmap
program, a separate utility that is
supplied with GrADS. gribmap
is executed from the command
line -- it scans the header in the GRIB files and constructs a
table to help GrADS navigate through the data.
For example, to make the GRIB map for the ETA data, the command would be:
gribmap -i eta.ctl <-o output-file>
By default, the output file will be called eta.map
. The map
file name is specified in the index
line of
eta.ctl
). You may use the -o option to specify a
different name for the map file, but you must also change the map file name
in eta.ctl
. gribmap
uses information in
eta.ctl
to make the map file, so be sure to make your
changes to the dates, etc. in eta.ctl
before
running gribmap.
You can use a similar utility called gribscan to examine
the structure of a GRIB data set directly. This is very useful for
customizing your own .ctl
files. The .ctl
files provided here do not allow access to all of the fields in the
NCEP data, just the more generally significant ones. Compare the output from
gribscan with one of the corresponding .ctl
files provided here.