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 = 7bit binary integer representing the exponent/characteristic
 B...B = 24bit binary integer, the mantissa.
The appropriate formula to recover the value of R is:
R = (1)^{s} * 2^{(24)} * B * 16^{(A64)}
2. Indicator Section
Byte/Octet  Description 
0104  "GRIB"  ASCII characters to flag data as GRIB data 
0507  Total number of bytes for all data 
08  GRIB edition  currently 1 
2. Product Definition Section (PDS)
Octet/Byte 
Description 
0103 
Length in bytes of PDS 
04 
Parameter table version number  currently 2 for international exchange 
05 

06 
Generating process or model ID (center dependent) 
07 
Grid identification  used for fixed grid types, GDS is used for specific grid definition 
08 

09 

10 

1112 

13  Reference Time  Year of century 
14  Month of year 
15  Day of month 
16  Hour of day 
17  Minute of hour 
18 

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 

2223 
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 subcenter 
2728 
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). 
2940 
Reserved (need not be present) 
41nnn 
Reserved for originating center use. 
3. Grid Description Section (GDS)
Byte/Octet 
Description 
0103 
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 

0732 
Grid description, according to data representation type, except Lambert, Mercator or Space View. 
0742 
Grid description for Lambert or Mercator grid 
0744 
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 quasiregular 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 "quasiregular" 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 
0708  Ni  No. of points along a latitude circle 
0910  Nj  No. of points along a longitude meridian 
1113  La_{1}  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 
1416  Lo_{1}  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 
1820  La_{2}  Latitude of last grid point (same units, value range, and bit 1 as La_{1}) 
2123  Lo_{2}  Longitude of last grid point (same units, value range, and bit 1 as Lo_{1}) 
2425  Di  Longitudinal Direction Increment (same units as Lo_{1}) (if not given, all bits set = 1) 
26  27  Regular Lat/Lon Grid: Dj  Latitudinal Direction Increment (same units as La_{1}) (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 quasiregular 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 78) or Nj (octets 910) and the corresponding Di (octets 2425) or Dj (octets 2627) shall be coded with all bits set to 1 (missing).
 A quasiregular 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 1116. The grid points shall be evenly spaced in latitude (longitude).
 For Gaussian grids only the rows can be rendered quasiregular; the first point shall be located at the meridian given in octets 1416 and the last point at the meridian given in octets 2123.
3.2 Grid Definition for Polar Stereographic Grids
Octet 
CONTENT & MEANING 
0708 
Nx  Number of points along xaxis 
0910 
Ny  Number of points along yaxis 
1113 
La1  Latitude of first grid point 
1416 
Lo1  Longitude of first grid point 
17 

1820 
Lov  The orientation of the grid; i.e., the east longitude value of the meridian which is parallel to the yaxis (or columns of the grid) along which latitude increases as the ycoordinate increases. (Note: The orientation longitude may, or may not, appear within a particular grid.) 
2123 
Dx  the Xdirection grid length (see note 2) 
2426 
Dy  the Ydirection grid length (see note 2) 
27 
Projection center flag (see note 5) 
28 

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 
0708 
Nx  Number of points along xaxis 
0910 
Ny  Number of points along yaxis 
1113 
La1  Latitude of first grid point 
1416 
Lo1  Longitude of first grid point 
17 

1820 
Lov  The orientation of the grid; i.e., the east longitude value of the meridian which is parallel to the yaxis (or columns of the grid) along which latitude increases as the ycoordinate increases. (Note: The orientation longitude may, or may not, appear within a particular grid.) 
2123 
Dx  the Xdirection grid length (see note 2) 
2426 
Dy  the Ydirection grid length (see note 2) 
27 
Projection center flag (see note 5) 
28 

2931 
Latin 1  The first latitude from the pole at which the secant cone cuts the spherical earth. (See Note 8) 
3234 
Latin 2  The second latitude from the pole at which the secant cone cuts the spherical earth. (See Note 8) 
3537 
Latitude of southern pole (millidegrees) 
3840 
Longitude of southern pole (millidegrees) 
4142 
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 
0708  Ni  Number of points along a latitude circle 
0910  Nj  Number of points along a longitude meridian 
1113  La1  Latitude of first grid point 
1416  Lo1  Longitude of first grid point 
17  Resolution and component flags 
1820  La2  latitude of last grid point 
2123  Lo2  longitude of last grid point 
2426  Latin  The latitude(s) at which the Mercator projection cylinder intersects the earth. 
27  Reserved (set to 0) 
28  Scanning mode 
2931  Di  the longitudinal direction increment (see Note 2) 
3234  Dj  the latitudinal direction increment (see note 2) 
3542  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 
0708 
Nx  number of points along x axis (columns) 
0910 
Ny  number of points along y axis (rows or lines) 
1113 
Lap  latitude of subsatellite point 
1416 
Lop  longitude of subsatellite point 
17 
Resolution and component flags (Table 7) 
1820 
dx  apparent diameter of earth in grid lengths, in x direction 
2123 
dy  apparent diameter of earth in grid lengths, in y direction 
2425 
Xp  Xcoordinate of sub satellite point 
2627 
Yp  Ycoordinate of subsatellite point 
28 
Scanning Mode (Table 8) 
2931 
the orientation of the grid; i.e., the angle in millidegrees between the increasing y axis and the meridian of the subsatellite point in the direction of increasing latitude (see Note 3). 
3234 
Nr  the altitude of the camera from the earth's center, measured in units of the earth's (equatorial) radius (See Note 4). 
3544 
reserved 
Notes:
 It is assumed that the satellite is at its nominal position, i.e., it is looking directly at its subsatellite point.
 Octet 3234 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 subsatellite point is the North pole; or the meridian 0 degrees, if the subsatellite 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 

0103 
Length in bytes of BMS 
04 
Number of unused bits at end of Section 3. 
0506 
Numeric: if 0: a bit map follows; 
07nnn 
Bit map, zero filled to an even number of octets 
5. Binary Data Section (BDS)
This section contains the packed binary data.
Octet 

0103 
Length in octets of binary data section 
04 
Bits 1 through 4: Flag 
0506 
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). 
0710 
Reference value (minimum value); floating point representation of the number. 
11 
Number of bits into which a datum point is packed 
12nnn 
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  
14  "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 MediumRange 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 
Area 
Grid Shape 
Gridpoints 

21 
5.0 x 2.5 
0180E, 090N 
37 
36 + pole 
1333 
22 
5.0 x 2.5 
180W0, 090N 
37 
36 + pole 
1333 
23 
5.0 x 2.5 
0180E, 90S0 
pole + 37 
36 
1333 
24 
5.0 x 2.5 
180W0, 90S0 
pole + 37 
36 
1333 
25 
5.0 x 5.0 
0355E, 090N 
72 
18 + pole 
1297 
26 
5.0 x 5.0 
0355E, 90S0 
pole + 72 
18 
1297 
61 
2.0 x 2.0 
0180E, 090N 
91 
45 + pole 
4096 
62 
2.0 x 2.0 
180W0, 090N 
91 
45 + pole 
4096 
63 
2.0 x 2.0 
0180E, 90S0 
pole + 91 
45 
4096 
64 
2.0 x 2.0 
180W0, 90S0 
pole + 91 
45 
4096 
255 
(nonstandard 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  
38  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  m^{2}/s^{2} 
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  Pseudoadiabatic 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  ucomponent of wind  m/s 
034  vcomponent of wind  m/s 
035  Stream function  m^{2}/s 
036  Velocity potential  m^{2}/s 
037  Montgomery stream function  m^{2}/s^{2} 
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 ucomponent shear  /s 
046  Vertical vcomponent shear  /s 
047  Direction of current  Deg. true 
048  Speed of current  m/s 
049  ucomponent of current  m/s 
050  vcomponent of current  m/s 
051  Specific humidity  kg/kg 
052  Relative humidity  % 
053  Humidity mixing ratio  kg/kg 
054  Precipitable water  kg/m^{2} 
055  Vapor pressure  Pa 
056  Saturation deficit  Pa 
057  Evaporation  kg/m^{2} 
058  Cloud Ice  kg/m^{2} 
059  Precipitation rate  kg/m^{2}/s 
060  Thunderstorm probability  % 
061  Total precipitation  kg/m^{2} 
062  Large scale precipitation  kg/m^{2} 
063  Convective precipitation  kg/m^{2} 
064  Snowfall rate water equivalent  kg/m^{2}s 
065  Water equiv. of accum. snow depth  kg/m^{2} 
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/m^{2} 
077  
078  Convective snow  kg/m^{2} 
079  Large scale snow  kg/m^{2} 
080  Water Temperature  K 
081  Landsea 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/m^{2} 
087  Vegetation  % 
088  Salinity  kg/kg 
089  Density  kg/m^{3} 
090  Water run off  kg/m^{2} 
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  ucomponent of ice drift  m/s 
096  vcomponent of ice drift  m/s 
097  Ice growth rate  m/s 
098  Ice divergence  /s 
099  Snow melt  kg/m^{2} 
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 shortwave radiation (surface)  W/m^{2} 
112  Net long wave radiation (surface)  W/m^{2} 
113  Net shortwave radiation (top of atmos.)  W/m^{2} 
114  Net long wave radiation (top of atmos.)  W/m^{2} 
115  Long wave radiation  W/m^{2} 
116  Short wave radiation  W/m^{2} 
117  Global radiation  W/m^{2} 
118  
119  
120  
121  Latent heat net flux  W/m^{2} 
122  Sensible heat net flux  W/m^{2} 
123  Boundary layer dissipation  W/m^{2} 
124  Momentum flux, u component  N/m^{2} 
125  Momentum flux, v component  N/m^{2} 
126  Wind mixing energy  J 
127  Image data  
128254  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  
1099 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  475theta of top (K)  475theta of bottom (K) 
121  layer between two pressure levels  1100pressure of top (hPA)  1100pressure of bottom (hPa) 
125  height level  height (cm)  
128  layer between two sigma levels  1.1sigma of top in 1/1000  1.1sigma of bottom in 1/1000 
141  layer between two pressure levels  pressure of top (kPa)  1100pressure 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 
8253  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 
0609 
reserved 
10 
P1 occupies octets 19 and 20; product valid at reference time + P1 
1150 
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 periodmeans that are averaged together to form the climatological value, assuming that the N periodmean fields are separated by one year. The reference time indicates the start of the Nyear climatology. N is given in octets 2223 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. 
52112 
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 1317, 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. 
125254 
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 
0612  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 

34 
reserved (set to 0) 

5 
0 
u and vcomponents 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 

68 
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  
912  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 nonzero 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.