GFS GRIB2 1.0 Data

Forecast Content

Below is a summarization of the flight planning data content:

Parameters and Levels

	SFC	850	700	600	500	450	400	350	300	250	200	150	100	Max	Trop
U Wind	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
V Wind	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
Temp	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X

DTN GFS 1.0 Also Contains

	SFC	850	700	600	500	450	400	350	300	250	200	150	100	Max	Trop
Pressure	X
Heights		X	X	X	X	X	X	X	X	X	X	X	X	X	X

 

Grid Resolution	MOne degree global Latitude / Longitude (NCEP Grid 3)
Forecast Interval	3 hours
Forecast Length	36 hours (0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36 hour forecasts)
File Counts	1 file for each Level 15 files for each forecast interval 13 forecast intervals Total 195 GR2 files for each forecast update
Update Period	Every 6 hours

File Packaging and Bundling

The flight planning data is packaged as a series of concatenated GRIB2 files. Individual GRIB2 files are concatenated such that one file contains GRIB2 sections for all of the parameters (wind U, wind V, and temperature) for a particular forecast period and atmospheric level.

The GRIB2 compression is defined in the header information included in the data files. For further information, review Section 4 Binary Data Section (BDS) found in the link below.
https://www.nco.ncep.noaa.gov/pmb/docs/on388/section4.html

Individual GRIB File Naming Convention

The flight planning files use the following file naming convention:
Filename definition:  <M><RT><LL><FF>.GR2
Where:

 

Model Code	Model Run-time Code	Level Code	Valid Forecast Hours
G=GFS H=DTN	00z       ( Filename Code= 00 ) 06z       ( Filename Code= 06 ) 12z       ( Filename Code= 12 ) 18z       ( Filename Code= 18 )	SFC                  ( Filename Code= 98 ) Max. Wind        ( Filename Code= 96 ) Tropopause      ( Filename Code= 97 ) 850mb              ( Filename Code= 85 ) 700mb              ( Filename Code= 70 ) 600mb              ( Filename Code= 60 ) 500mb              ( Filename Code= 50 ) 450mb              ( Filename Code= 45) 400mb              ( Filename Code= 40 ) 300mb              ( Filename Code= 30 ) 250mb              ( Filename Code= 25 ) 200mb              ( Filename Code= 20 ) 150mb              ( Filename Code= 15 ) 100mb              ( Filename Code= 10 )	0           ( Filename Code= IE) 3           ( Filename Code= IF) 6           ( Filename Code= IG ) 9           ( Filename Code= IJ ) 12         ( Filename Code= IM ) 15         ( Filename Code= IP ) 18         ( Filename Code= IS ) 21         ( Filename Code= IV ) 24         ( Filename Code= IY ) 27         ( Filename Code= I1 ) 30         ( Filename Code= I4 ) 33         ( Filename Code= I7 ) 36         ( Filename Code= JA )

File structure

As mentioned above, each flight planning file contains a concatenation of the GRIB2 files for all of the parameters (wind U, wind V, and temperature) for a particular forecast period and atmospheric level.

The structure of each flight planning file is very simple: the GRIB2 sections for each parameter are appended one after another to the file. The resulting file is a series of GRIB2s, with a marker at the head of each GRIB2 and a marker at the end of each GRIB2. These markers can be used to locate and extract the GRIB2s from the concatenated file. The head marker is the ASCII text “GRIB”; the tail marker is a sequence of four ASCII 7’s, as in “7777”.

See Figure 4-1 below:

[start of file]
…..
“GRIB” … [GRIB2 content] … “7777”
…
“GRIB” … [GRIB2 content] … “7777”
…
[end of file]

Figure 4-1 Structure of concatenated file.

Please take note of the following:

No assumptions should be made regarding the position of the GRIB2 file within the concatenated file. The first GRIB2 may or may not begin at the start of the file. There may be non-GRIB2 data (headers, etc) leading or trailing the GRIB2 sections.