GRIB Format

Edition 1

1. GRIB Overview

The GRIB product is broken down into several subsections:

Indicator Section
Product Definition Section (PDS)
Grid Description Section (GDS) - optional
Bit Map Section (BMS) - optional
Binary Data Section (BDS)
End Section

Tables:

Originating Centers
Process/Model ID
Grid Indentifiers
GDS/BMS Flag
Parameter and Units
Level or Layer
Forecast Time Units
Time Range Indicator
Data Representation Type
Resolution and Component Flags
Scanning Mode Flag
BDS Flag

Each section is described below.

1.1 Data Packing

The values saved in a GRIB file are packed. The actual data value is derived from the following parameters:

X = internal value saved in the binary data section. The values depend on the number of bits per grid value.
D = decimal scale factor
E = binary scale factor (sign bit plus 15 bit integer)
R = reference value

Each gridpoint value (Y) is determined from the following formula:

Y * 10^D = R + (X * 2^E)

The reference value (R) uses IBM single precision floating point format.

sAAAAAAA BBBBBBBB BBBBBBBB BBBBBBBB

s = sign bit, encoded as 0 means positive, 1 means negative
A...A = 7-bit binary integer representing the exponent/characteristic
B...B = 24-bit binary integer, the mantissa.

The appropriate formula to recover the value of R is:

R = (-1)^s * 2^(-24) * B * 16^(A-64)

2. Indicator Section

Byte/Octet	Description
01-04	"GRIB" - ASCII characters to flag data as GRIB data
05-07	Total number of bytes for all data
08	GRIB edition - currently 1

2. Product Definition Section (PDS)

Octet/Byte	Description
01-03	Length in bytes of PDS
04	Parameter table version number - currently 2 for international exchange
05	Originating Center
06	Generating process or model ID (center dependent)
07	Grid identification - used for fixed grid types, GDS is used for specific grid definition
08	Flag specifying the presence or absence of a GDS or a BMS
09	Parameter and units
10	Level or Layer Type
11-12	Level or Layer values
13	Reference Time - Year of century
14	Month of year
15	Day of month
16	Hour of day
17	Minute of hour
18	Forecast time unit
19	P1 - Period of time (Number of time units). 0 for analysis or initialized analysis.
20	P2 - Period of time (Number of time units) or time interval between successive analyses, successive initialized analyses, or forecasts, undergoing averaging or accumulation.
21	Time range indicator
22-23	Number included in average, when octet 21 (Table 5) indicates an average or accumulation; otherwise set to zero.
24	Number Missing from averages or accumulations.
25	Century of Initial (Reference) time (=20 until Jan. 1, 2001, 21 afterwards)
26	Identification of sub-center
27-28	The decimal scale factor D. A negative value is indicated by setting the high order bit (bit No. 1) in octet 27 to 1 (on).
29-40	Reserved (need not be present)
41-nnn	Reserved for originating center use.

3. Grid Description Section (GDS)

Byte/Octet	Description
01-03	Length in bytes of the GDS
04	NV, the number of vertical coordinate parameters
05	PV, the location (octet number) of the list of vertical coordinate parameters, if present or PL, the location (octet number) of the list of numbers of points in each row (when no vertical parameters are present), if present or (all bits set to 1) if neither are present
06	Data representation type
07-32	Grid description, according to data representation type, except Lambert, Mercator or Space View.
07-42	Grid description for Lambert or Mercator grid
07-44	Grid description for Space View perspective grid
PV	List of vertical coordinate parameters. length = NV x 4 octets; if present, then PL = 4 x NV + PV
PL	List of numbers of points in each row, used for quasi-regular grids. length = NROWS x 2 octets, where NROWS is the total number of rows defined within the grid description

Note: NV and PV relate to features of GRIB not, at present, in use in international exchange. See the WMO Manual on Codes for the descriptions of those features.

PL is used for "quasi-regular" or "thinned" grids; e.g., a lat/lon grid where the number of points in each row is reduced as one moves poleward from the equator. The reduction usually follows some mathematical formula involving the cosine of the latitude, to generate an (approximately) equally spaced grid array. The association of the numbers in octet PL (and following) with the particular row follows the scanning mode specification in Table 8.

3.1 Grid Definition for Latitude/Longitude Grids

Octet/Byte	Description
07-08	Ni - No. of points along a latitude circle
09-10	Nj - No. of points along a longitude meridian
11-13	La₁ - latitude of first grid point units: millidegrees (degrees x 1000) values limited to range 0 - 90,000 bit 1 (leftmost) set to 1 for south latitude
14-16	Lo₁ - longitude of first grid point units: millidegrees (degrees x 1000) values limited to range 0 - 360,000 bit 1 (leftmost) set to 1 for west longitude
17	Resolution and component flags
18-20	La₂ - Latitude of last grid point (same units, value range, and bit 1 as La₁)
21-23	Lo₂ - Longitude of last grid point (same units, value range, and bit 1 as Lo₁)
24-25	Di - Longitudinal Direction Increment (same units as Lo₁) (if not given, all bits set = 1)
26 - 27	Regular Lat/Lon Grid: Dj - Latitudinal Direction Increment (same units as La₁) (if not given, all bits set = 1) Gaussian Grid: N - number of latitude circles between a pole and the equator. Mandatory if Gaussian Grid specified
28	Scanning mode flags
29 - 32	Reserved (set to zero)

Notes:

The latitude and longitude of the first and last grid points should always be given, for regular grids.
If a quasi-regular grid is to be described, in which all the rows or columns do not necessarily have the same number of grid points, either Ni (octets 7-8) or Nj (octets 9-10) and the corresponding Di (octets 24-25) or Dj (octets 26-27) shall be coded with all bits set to 1 (missing).
A quasi-regular grid can be defined only for rows or columns, but not both simultaneously. The first point in each row (column) shall be positioned at the meridian (parallel) indicated in octets 11-16. The grid points shall be evenly spaced in latitude (longitude).
For Gaussian grids only the rows can be rendered quasi-regular; the first point shall be located at the meridian given in octets 14-16 and the last point at the meridian given in octets 21-23.

3.2 Grid Definition for Polar Stereographic Grids

Octet	CONTENT & MEANING
07-08	Nx - Number of points along x-axis
09-10	Ny - Number of points along y-axis
11-13	La1 - Latitude of first grid point
14-16	Lo1 - Longitude of first grid point
17	Resolution and component flags
18-20	Lov - The orientation of the grid; i.e., the east longitude value of the meridian which is parallel to the y-axis (or columns of the grid) along which latitude increases as the y-coordinate increases. (Note: The orientation longitude may, or may not, appear within a particular grid.)
21-23	Dx - the X-direction grid length (see note 2)
24-26	Dy - the Y-direction grid length (see note 2)
27	Projection center flag (see note 5)
28	Scanning mode
29 - 32	Set to 0 (reserved)

Notes:

Latitude and longitude are in millidegrees (thousandths)
Grid lengths are in units of meters, at the 60 degree latitude circle nearest to the pole in the projection plane.
Latitude values are limited to the range 0 - 90,000. Bit 1 is set to 1 to indicate south latitude.
Longitude values are limited to the range 0 - 360,000. Bit one is set to 1 to indicate west longitude.
Projection Center Flag - Bit 1 set to 0 if the North pole is on the projection plane. Bit 1 set to 1 if the South pole is on the projection plane.
The first and last grid points may not necessarily be the same as the first and last data points if the bit map section (BMS) is used.
The resolution flag (bit 1 of Table 7) is not applicable.

3.3 Grid Definition for Lambert Conformal, Conic Grids

Octet	CONTENT & MEANING
07-08	Nx - Number of points along x-axis
09-10	Ny - Number of points along y-axis
11-13	La1 - Latitude of first grid point
14-16	Lo1 - Longitude of first grid point
17	Resolution and component flags
18-20	Lov - The orientation of the grid; i.e., the east longitude value of the meridian which is parallel to the y-axis (or columns of the grid) along which latitude increases as the y-coordinate increases. (Note: The orientation longitude may, or may not, appear within a particular grid.)
21-23	Dx - the X-direction grid length (see note 2)
24-26	Dy - the Y-direction grid length (see note 2)
27	Projection center flag (see note 5)
28	Scanning mode
29-31	Latin 1 - The first latitude from the pole at which the secant cone cuts the spherical earth. (See Note 8)
32-34	Latin 2 - The second latitude from the pole at which the secant cone cuts the spherical earth. (See Note 8)
35-37	Latitude of southern pole (millidegrees)
38-40	Longitude of southern pole (millidegrees)
41-42	Reserved (set to 0)

Notes:

Latitude and longitude are in millidegrees (thousandths)
Grid lengths are in units of meters, at the intersection latitude circle nearest to the pole in the projection plane.
Latitude values are limited to the range 0 - 90,000. Bit 1 is set to 1 to indicate south latitude.
Longitude values are limited to the range 0 - 360,000. Bit one is set to 1 to indicate west longitude.
Octet 27:
Bit 1 set to 0 if the North pole is on the projection plane.
Bit 1 set to 1 if the South pole is on the projection plane.
Bit 2 set to 0 if only one projection center used
Bit 2 set to 1 if projection is bipolar and symmetric
The first and last grid points may not necessarily be the same as the first and last data points if the bit map section (BMS) is used.
The resolution flag (bit 1 of Table 7) is not applicable.
If Latin 1 = Latin 2 then the projection is on a tangent cone.

3.4 Grid Definition for Mercator Grids

Octet	CONTENT & MEANING
07-08	Ni - Number of points along a latitude circle
09-10	Nj - Number of points along a longitude meridian
11-13	La1 - Latitude of first grid point
14-16	Lo1 - Longitude of first grid point
17	Resolution and component flags
18-20	La2 - latitude of last grid point
21-23	Lo2 - longitude of last grid point
24-26	Latin - The latitude(s) at which the Mercator projection cylinder intersects the earth.
27	Reserved (set to 0)
28	Scanning mode
29-31	Di - the longitudinal direction increment (see Note 2)
32-34	Dj - the latitudinal direction increment (see note 2)
35-42	Reserved (set to 0)

Notes:

Latitude and longitude are in millidegrees (thousandths)
Grid lengths are in units of meters, at the circle of latitude specified by Latin.
Latitude values are limited to the range 0 - 90,000. Bit 1 is set to 1 to indicate south latitude.
Longitude values are limited to the range 0 - 360,000. Bit one is set to 1 to indicate west longitude.
The latitude and longitude of the last grid point should always be given.
The first and last grid points may not necessarily be the same as the first and last data points if the bit map section (BMS) is used.

3.5 Grid Definition for Space View or Orthographic

Octet	CONTENTS
07-08	Nx - number of points along x axis (columns)
09-10	Ny - number of points along y axis (rows or lines)
11-13	Lap - latitude of sub-satellite point
14-16	Lop - longitude of sub-satellite point
17	Resolution and component flags (Table 7)
18-20	dx - apparent diameter of earth in grid lengths, in x direction
21-23	dy - apparent diameter of earth in grid lengths, in y direction
24-25	Xp - X-coordinate of sub satellite point
26-27	Yp - Y-coordinate of sub-satellite point
28	Scanning Mode (Table 8)
29-31	the orientation of the grid; i.e., the angle in millidegrees between the increasing y axis and the meridian of the sub-satellite point in the direction of increasing latitude (see Note 3).
32-34	Nr - the altitude of the camera from the earth's center, measured in units of the earth's (equatorial) radius (See Note 4).
35-44	reserved

Notes:

It is assumed that the satellite is at its nominal position, i.e., it is looking directly at its sub-satellite point.
Octet 32-34 shall be set to all ones (missing) to indicate the orthographic view (from infinite distance).
It is the angle between increasing y axis and the meridian 180 degrees east if the sub-satellite point is the North pole; or the meridian 0 degrees, if the sub-satellite point is the south pole.
The apparent angular size of the earth will be given by 2 x asin(1/Nr).
The horizontal and vertical angular resolutions of he sensor (Rx and Ry), needed for navigation equations, can be calculated from the following

Rx = 2 x asin(1/Nr) / dx
Ry = 2 x asin(1/Nr) / dy

4. Bit Map Section (BMS)

This section defines which grid points will be presented in the Binary Data Section. A 1 value indicates a value will appear. A 0 value means it will be absent.

Octet
01-03	Length in bytes of BMS
04	Number of unused bits at end of Section 3.
05-06	Numeric: if 0: a bit map follows; otherwise: the numeric refers to a predefined bit map provided by the center
07-nnn	Bit map, zero filled to an even number of octets

5. Binary Data Section (BDS)

This section contains the packed binary data.

Octet
01-03	Length in octets of binary data section
04	Bits 1 through 4: Flag Bits 5 through 8: Number of unused bits at end of Section 4.
05-06	The binary scale factor (E). A negative value is indicated by setting the high order bit (bit No. 1) in octet 5 to 1 (on).
07-10	Reference value (minimum value); floating point representation of the number.
11	Number of bits into which a datum point is packed
12-nnn	Variable, depending on octet 4; zero filled to an even number of octets.
14	Optionally, may contain an extension of the flags in octet 4.

6. End Section

This is a key sequence used to denote the end of a GRIB product.

Octet
1-4	"7777"

A. Originating Centers (PDS)

Value	Contents
07	US Weather Service - National Met. Center
08	US Weather Service - NWS Telecomms Gateway
09	US Weather Service - Field Stations
34	Japanese Meteorological Agency - Tokyo
52	National Hurricane Center, Miami
54	Canadian Meteorological Service - Montreal
57	U.S. Air Force - Global Weather Center
58	US Navy - Fleet Numerical Oceanography Center
59	NOAA Forecast Systems Lab, Boulder CO
74	U.K. Met Office - Bracknell
85	French Weather Service - Toulouse
97	European Space Agency (ESA)
98	European Center for Medium-Range Weather Forecasts - Reading
99	DeBilt, Netherlands

B. Process/Model ID

NCEP values:

Value	Contents
10	Significant Wind Wave model
19	LFM model
25	Snow Cover analysis
39	NGM model
43	Global Optimal Interpolation analysis
44	Sea Surface Temperature analysis
46	Spectral model - 30 wave
53	LFM analysis
64	Regional Optimal Interpolation analysis
69, 77, 81, 96	Aviation (AVN) model
78, 80, 82, 94	Medium Range Forecast (MRF) model
83, 84, 85, 89	Eta model
86	RUC model

C. Grid Indentifiers

International Exchange Grids

Value	Resolution degree lonxlat	Area Coverage	Grid Shape Row/Columns		Gridpoints
21	5.0 x 2.5	0-180E, 0-90N	37	36 + pole	1333
22	5.0 x 2.5	180W-0, 0-90N	37	36 + pole	1333
23	5.0 x 2.5	0-180E, 90S-0	pole + 37	36	1333
24	5.0 x 2.5	180W-0, 90S-0	pole + 37	36	1333
25	5.0 x 5.0	0-355E, 0-90N	72	18 + pole	1297
26	5.0 x 5.0	0-355E, 90S-0	pole + 72	18	1297
61	2.0 x 2.0	0-180E, 0-90N	91	45 + pole	4096
62	2.0 x 2.0	180W-0, 0-90N	91	45 + pole	4096
63	2.0 x 2.0	0-180E, 90S-0	pole + 91	45	4096
64	2.0 x 2.0	180W-0, 90S-0	pole + 91	45	4096
255	(non-standard grid - defined in the GDS)

D. GDS/BMS Flag

BIT	VALUE	MEANING
1	0	GDS Omitted
	1	GDS Included
2	0	BMS Omitted
	1	BMS Included
3-8	0	reserved

E. Parameter and Units

VALUE	PARAMETER	UNITS
000	Reserved
001	Pressure	Pa
002	Pressure reduced to MSL	Pa
003	Pressure tendency	Pa/s
004
005
006	Geopotential	m²/s²
007	Geopotential height	Gpm
008	Geometric height	M
009	Standard deviation of height	M
010
011	Temperature	K
012	Virtual temperature	K
013	Potential temperature	K
014	Pseudo-adiabatic potential temperature	K
015	Maximum temperature	K
016	Minimum temperature	K
017	Dew point temperature	K
018	Dew point depression (or deficit)	K
019	Lapse rate	K/m
020	Visibility	M
021	Radar Spectra (1)	-
022	Radar Spectra (2)	-
023	Radar Spectra (3)	-
024
025	Temperature anomaly	K
026	Pressure anomaly	Pa
027	Geopotential height anomaly	Gpm
028	Wave Spectra (1)	-
029	Wave Spectra (2)	-
030	Wave Spectra (3)	-
031	Wind direction	Deg. true
032	Wind speed	m/s
033	u-component of wind	m/s
034	v-component of wind	m/s
035	Stream function	m²/s
036	Velocity potential	m²/s
037	Montgomery stream function	m²/s²
038	Sigma coord. vertical velocity	s /s
039	Pressure Vertical velocity	Pa/s
040	Geometric Vertical velocity	m/s
041	Absolute vorticity	/s
042	Absolute divergence	/s
043	Relative vorticity	/s
044	Relative divergence	/s
045	Vertical u-component shear	/s
046	Vertical v-component shear	/s
047	Direction of current	Deg. true
048	Speed of current	m/s
049	u-component of current	m/s
050	v-component of current	m/s
051	Specific humidity	kg/kg
052	Relative humidity	%
053	Humidity mixing ratio	kg/kg
054	Precipitable water	kg/m²
055	Vapor pressure	Pa
056	Saturation deficit	Pa
057	Evaporation	kg/m²
058	Cloud Ice	kg/m²
059	Precipitation rate	kg/m²/s
060	Thunderstorm probability	%
061	Total precipitation	kg/m²
062	Large scale precipitation	kg/m²
063	Convective precipitation	kg/m²
064	Snowfall rate water equivalent	kg/m²s
065	Water equiv. of accum. snow depth	kg/m²
066	Snow depth	M
067	Mixed layer depth	M
068	Transient thermocline depth	M
069	Main thermocline depth	M
070	Main thermocline anomaly	M
071	Total cloud cover	%
072	Convective cloud cover	%
073	Low cloud cover	%
074	Medium cloud cover	%
075	High cloud cover	%
076	Cloud water	kg/m²
077
078	Convective snow	kg/m²
079	Large scale snow	kg/m²
080	Water Temperature	K
081	Land-sea mask	Fraction
	(1=land;0=sea) (see note)
082	Deviation of sea level from mean	M
083	Surface roughness	M
084	Albedo	%
085	Soil temperature	K
086	Soil moisture content	kg/m²
087	Vegetation	%
088	Salinity	kg/kg
089	Density	kg/m³
090	Water run off	kg/m²
091	Ice concentration	Fraction
	(ice=1;no ice=0)(see note)
092	Ice thickness	M
093	Direction of ice drift	deg. true
094	Speed of ice drift	m/s
095	u-component of ice drift	m/s
096	v-component of ice drift	m/s
097	Ice growth rate	m/s
098	Ice divergence	/s
099	Snow melt	kg/m²
100	Significant height of combined wind	m
	waves and swell
101	Direction of wind waves	deg. true
102	Significant height of wind waves	m
103	Mean period of wind waves	s
104	Direction of swell waves	deg. true
105	Significant height of swell waves	m
106	Mean period of swell waves	s
107	Primary wave direction	deg. true
108	Primary wave mean period	s
109	Secondary wave direction	deg. true
110	Secondary wave mean period	s
111	Net short-wave radiation (surface)	W/m²
112	Net long wave radiation (surface)	W/m²
113	Net short-wave radiation (top of atmos.)	W/m²
114	Net long wave radiation (top of atmos.)	W/m²
115	Long wave radiation	W/m²
116	Short wave radiation	W/m²
117	Global radiation	W/m²
118
119
120
121	Latent heat net flux	W/m²
122	Sensible heat net flux	W/m²
123	Boundary layer dissipation	W/m²
124	Momentum flux, u component	N/m²
125	Momentum flux, v component	N/m²
126	Wind mixing energy	J
127	Image data
128-254	Reserved for use by originating center)
255	Missing

F. Level or Layer

Octet 10 - Type of level/layer	Octet 11 - Value 1	Octet 12 - Value 2
00 - reserved
01 - surface of earth including sea surface
02 - cloud base
03 - cloud top
04 - freezing level (0C)
05 - adiabatic condensation level
06 - maximum wind level
07 - tropopause level
08 - nominal top of atmosphere
09 - sea bottom
10-99 reserved
100 - isobaric level	pressure in hectoPascals (hPa)
101 - layer between two isobaric levels	pressure of top (kPa)	pressure of bottom (kPa)
102 - mean sea level	0	0
103 - fixed height level above mean sea level (MSL)	height in meters
104 - layer between two height levels above MSL	height of top (hm)	height of bottom (hm)
105 - fixed height above ground level	height in meters
106 - layer between two height levels above ground	height of top (hm)	height of bottom (hm)
107 - sigma level	sigma value in 1/10000
108 - layer between two sigma levels	value at top in 1/100	value at bottom in 1/100
109 - hybrid level	level number
110 - layer between two hybrid levels	level number of top	level number of bottom
111 - depth below surface	centimeters
112 - layer between two levels below surface	depth of top (cm)	depth of bottom (cm)
113 - isentropic level	potential temperature (K)
114 - layer between two isentropic levels	475-theta of top (K)	475-theta of bottom (K)
121 - layer between two pressure levels	1100-pressure of top (hPA)	1100-pressure of bottom (hPa)
125 - height level	height (cm)
128 - layer between two sigma levels	1.1-sigma of top in 1/1000	1.1-sigma of bottom in 1/1000
141 - layer between two pressure levels	pressure of top (kPa)	1100-pressure of bottom (hPa)
160 - depth below sea level	depth (m)
200 - entire atmosphere
201 - entire ocean

G. Forecast Time Units

VALUE	TIME UNIT
0	minute
1	hour
2	day
3	month
4	year
5	decade
6	normal (30 years)
7	century
8-253	reserved
254	second

H. Time Range Indicator

VALUE	MEANING
00	Forecast product valid at reference time + P1 P1>0), or uninitialized analysis product for reference time (P1=0) or image product for reference time (P1=0)
01	Initialized analysis product for reference time (P1=0).
02	Product with a valid time ranging between reference time + P1 and reference time + P2
03	Average (reference time + P1 to reference time + P2)
04	Accumulation (reference time + P1 to reference time + P2). Product considered valid at reference time + P2
05	Difference(reference time + P2 minus reference time + P1) product considered valid at reference time + P2
06-09	reserved
10	P1 occupies octets 19 and 20; product valid at reference time + P1
11-50	reserved
51	Climatological Mean Value: multiple year averages of quantities which are themselves means over some period of time (P2) less than a year. The reference time (R) indicates the date and time of the start of a period of time, given by R to R + P2, over which a mean is formed; N indicates the number of such period-means that are averaged together to form the climatological value, assuming that the N period-mean fields are separated by one year. The reference time indicates the start of the N-year climatology. N is given in octets 22-23 of the PDS. If P1 = 0 then the data averaged in the basic interval P2 are assumed to be continuous, i.e., all available data are simply averaged together. If P1 = 1 (the units of time - octet 18, code table 4 - are not relevant here) then the data averaged together in the basic interval P2 are valid only at the time (hour, minute) given in the reference time, for all the days included in the P2 period. The units of P2 are given by the contents of octet 18 and Table 4.
52-112	reserved
113	Average of N forecasts (or initialized analyses); each product has forecast period of P1 (P1=0 for initialized analyses); products have reference times at intervals of P2, beginning at the given reference time.
114	Accumulation of N forecasts (or initialized analyses); each product has forecast period of P1 (P1=0 for initialized analyses); products have reference times at intervals of P2, beginning at the given reference time.
115	Average of N forecasts, all with the same reference time; the first has a forecast period of P1, the remaining forecasts follow at intervals of P2.
116	Accumulation of N forecasts, all with the same reference time; the first has a forecast period of P1, the remaining follow at intervals of P2.
117	Average of N forecasts, the first has a period of P1, the subsequent ones have forecast periods reduced from the previous one by an interval of P2; the reference time for the first is given in octets 13-17, the subsequent ones have reference times increased from the previous one by an interval of P2. Thus all the forecasts have the same valid time, given by the initial reference time + P1.
118	Temporal variance, or covariance, of N initialized analyses; each product has forecast period P1=0; products have reference times at intervals of P2, beginning at the given reference time.
119 -122	reserved
123	Average of N uninitialized analyses, starting at the reference time, at intervals of P2.
124	Accumulation of N uninitialized analyses, starting at the reference time, at intervals of P2.
125-254	reserved

I. Data Representation Type

VALUE	MEANING
00	Latitude/Longitude Grid also called Equidistant Cylindrical or Plate Carree projection grid
01	Mercator Projection Grid
02	Gnomonic Projection Grid
03	Lambert Conformal, secant or tangent, conical or bipolar (normal or oblique) Projection Grid
04	Gaussian Latitude/Longitude Grid
05	Polar Stereographic Projection Grid
06-12	reserved - see Manual on Codes
13	Oblique Lambert conformal, secant or tangent, conical or bipolar, projection
14 - 49	reserved - see Manual on Codes
50	Spherical Harmonic Coefficients
51 - 89	reserved - see Manual on Codes
90	Space view perspective or orthographic grid
91 - 254	reserved - see Manual on Codes

J. Resolution and Component Flags

Bit	Value	Meaning
1	0	Direction increments not given
	1	Direction increments given
2	0	Earth assumed spherical with radius = 6367.47 km
	1	Earth assumed oblate spheroid with size
		as determined by IAU in 1965:
		6378.160 km, 6356.775 km, f = 1/297.0
3-4		reserved (set to 0)
5	0	u- and v-components of vector quantities resolved relative to easterly and northerly directions
	1	u and v components of vector quantities resolved relative to the defined grid in the direction of increasing x and y (or i and j) coordinates respectively
6-8		reserved (set to 0)

Note: If the GDS is not included in a message then any wind components are assumed to be resolved relative to the grid specified in the PDS with u and v defined as positive in the direction of increasing x and y (or i and j) coordinates respectively.

K. Scanning Mode Flag

BIT	VALUE	MEANING
1	0	Points scan in +i direction
	1	Points scan in -i direction
2	0	Points scan in -j direction
	1	Points scan in +j direction
3	0	Adjacent points in i direction are consecutive (FORTRAN: (I,J))
	1	Adjacent points in j direction are consecutive (FORTRAN: (J,I))

Note: i direction is defined as west to east along a parallel of latitude, or left to right along an x axis. j direction is defined as south to north along a meridian of longitude, or bottom to top along a y axis.

L. BDS Flag

BIT	VALUE	MEANING
1	0	Grid point data
	1	Spherical Harmonic Coefficients
2	0	Simple packing
	1	Second order ("Complex") Packing
3	0	Original data were floating point values
	1	Original data were integer values
4	0	No additional flags at octet 14
	1	Octet 14 contains flag bits 5 - 12

The following gives the meaning of the bits in octet 14 ONLY if bit 4 is set to 1. Otherwise octet 14 contains regular binary data.

5		Reserved (set to 0)
6	0	Single datum at each grid point
	1	Matrix of values at each grid point
7	0	No secondary bit maps
	1	Secondary bit maps present
8	0	Second order values have constant width
	1	Second order values have different widths
9-12		Reserved (set to 0)

Notes:

Bit 3 is set to 1 to indicate that the original data were integers; when this is the case any non-zero reference values should be rounded to an integer value prior to placing in the GRIB BDS.
Bit 4 is set to 1 to indicate that bits 5 to 12 are contained in octet 14 of the data section.
Although GRIB is not capable of representing a matrix of data values at each grid point, the meaning of bit 6 is retained in anticipation of a future capability.
When secondary bit maps are present in the data (used in association with second order packing) this is indicated by setting bit 7 to 1.
When octet 14 contains the extended flag information, octets 12 and 13 will also contain "special" information; the actual data will begin in a subsequent octet. See above.