The NCEP analysis and forecast data are available in grib format from NCEP's anonymous FTP site: ftp://ftp.ncep.noaa.gov. Data from a many different forecast models are available. For a complete listing, go to the pub/data/grib/ directory. This page provides guidance for viewing forecasts from three of the models: the ETA model, the Aviation model (AVN), and the Medium Range Forecast model (MRF).
Note: The ftp servers at NCEP are being upgraded and remodeled and the information here may become outdated at any time.
| 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.