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About the NDFD GRIB2 Decoder
The National Digital Forecast Database (NDFD) is a database put
together by the National Weather Service (NWS) to provide forecasts of sensible
weather elements (e.g., cloud cover, maximum temperature) on a seamless
grid. The NDFD is currently given out to the public as a
GRIB2 file. For more information about how and why the NDFD
was created, please see the NDFD
GRIB2 is the second version of the World Meterological
Organization's (WMO) standard for distributing gridded data. It is
described in the
WMO GRIB2 Document FM92-X11 GRIB. For "web friendly"
- click here
(Provided by the National Centers for Environmental Prediction (NCEP), it has
complete tables, but is missing the notes and regulations.)
The problem, when the NDFD first came out, was that the only way to
decode a GRIB2 message was to use the GRIB2 library. This
required the user to write code, and
then refer to the WMO's specifications to decipher the "meta" data (e.g.,
variable type, variable unit, reference date time, valid date time, etc).
This defeated the original purpose of the NDFD which was to make the digital
data easy to use by the public.
To resolve this the Meteorological
Development Laboratory (MDL) created a driver for the GRIB2
library. The driver, known as "degrib" (aka "NDFD GRIB2 decoder"), was
originally designed to:
- Provide an example of how to use the GRIB2 Decoder library by
making documented source code available to users. Since the time that
NDFD came out, NCEP has created a more complete
Since people were familiar with the degrib driver, MDL continued to maintain
the degrib driver program, but has transitioned to using the NCEP library.
- Be able to convert from GRIB2 to selected file formats such as
ESRI shapefiles (.shp), ASCII comma sepearated files (.csv), NetCDF
files, and binary float files (.flt) (useful in conjunction with GrADS, ESRI
ArcGIS, or ESRI ArcView 3 + Spatial Analyst extension).
- Enable users to understand the "meta" data produced by the GRIB2 library
without needing to refer to the WMO's specifications by creating an ASCII
(.txt) file that does the necessary lookups in the WMO's GRIB2 specification
To encourage the use of the NDFD, degrib was designed to run
either via a Graphical User Interface (GUI), or from the command line, giving
the user the flexibility to run the program manually or via a script or program.
For additional portablilty, the GUI aspect of degrib uses
Tcl/Tk (version 8.3.2).
Where do I go from here?