GRIB2 Encoding Details for the National Weather Service Digital Forecast Database

Background

The National Weather Service (NWS) is creating a National Digital Forecast  Database (NDFD) which will contain gridded forecasts of several weather elements.  In general, the weather parameters in the NDFD will be ground-based, sensible weather elements.  The forecast grids  that comprise the NDFD will come from multiple sources, including the NWS' Weather Forecast Offices   (WFO) and the National Centers for Environmental  Prediction (NCEP).  The World Meteorological Organization (WMO) has  adopted Edition 2 of the GRIB code as a standard for sharing GRI dded B inary data.  GRIB, Edition 2 (GRIB2) will be involved  in the NDFD in two ways.  GRIB2 will be one of the primary formats used to transmit NDFD data to NWS customers and partners.

The purpose of this document is to describe, in detail, the techniques that will be used to encode NWS forecasts into NDFD GRIB2 bulletins.  When dealing with a code as general and as flexible as GRIB2, one often encounters multiple, plausible ways to accomplish the encoding task.  It is hoped that this document will clarify the many decisions made during the creation of the NDFD.

In summer of 2011, NDFD will begin making experimental CONUS GRIB2 files available that contain finer spatial resolution (2.5 km) and higher temporal resolution ( 1-hr, for Days 1-3) grids.

References

This document will assume that the reader has access to and a working knowledge of the WMO publication FM 92-XII GRIB General Regularly-distributed Information in Binary Form.  This link should provide access to a version that has been formatted for web access.  Additionally, the following links provide access to several documents that describe encode/ decode routines developed by the NWS' Meteorological Development Laboratory (MDL).  These documents provide valuable commentary on some of the fields used in the GRIB2 code form.

The NWS has created an NDFD information web page.  There you will find the latest news regarding NDFD plans and recent developments.  In addition, MDL developers have written software that may be downloaded and used for accessing and decoding NDFD GRIB2 files from the NWS Telecommunications Gateway (NWSTG).  To obtain the latest version of this software, follow this link.

File, and Bulletin Structure

A single file will contain multiple GRIB2 bulletins.  One file will contain multiple forecast projections for a given weather element covering a specific geographic region.  There are NDFD grids available for the lower 48 states (CONUS), 16 different CONUS sub-sectors, Puerto Rico, Hawaii, Guam, and Alaska.  For Tropical Prediction Center grids, there are two additional domains.  One domain covers the area defined by NCEP's AWIPS 227 grid.   The other domain covers the Northern Pacific, as defined by NCEP's AWIPS 204 grid.  See this link for a detailed list of geographic sectors, filenames, and WMO header information with regards to NDFD data.

GRIB2 files for a given element and region will be split into two files, one containing the forecast grids for the period Day 1 through Day 3, the other containing the forecast grids for the period Day 4 through Day 7.  These files are located in different directories at the NWSTG FTP download site.

Every NDFD GRIB file begins with a flag field separator of the format:

****nnnnnnnnnn****\lf

where the "nnnnnnnnnn" is the size in bytes of the file, (minus the separator),   right justified with leading zeroes, and with a trailing "\lf".  The "\lf" character represents a single octet with the decimal value of 10.  The size of the Flag field separator is 19 bytes.

Following the flag field separator is a WMO "super header".  Check  this  link for the specific format of NDFD WMO headers.  The WMO super header  is 21  bytes long, the trailing "\cr\cr\lf" inclusive.  The "\cr" character represents a single octet with the decimal value of 13.  Immediately  following the super header is another flag field separator for the first GRIB2 bulletin in the file.  It contains the size of the bulletin to follow.

The bulletin itself begins with a WMO header.  Again, refer to the link above to get detailed information regarding the format of  the header.  The header contains the valid time of the GRIB2 bulletin.  The WMO  header is also 21 bytes long, the trailing "\cr\cr\lf" inclusive.  Following the header is the packed GRIB2 grid.  It begins with the ASCII text "GRIB"  and ends with the ASCII text "7777".  The packed data contains all the GRIB2 sections for that grid, as well as the packed grid.

Here's an example of the file format (individual components are bracketed with "< >"):

<file flag field separator\lf>
<WMO super header\cr\cr\lf>
<bulletin 1 flag field separator\lf>
<WMO header 1 for bulletin\cr\cr\lf>
<"GRIB"packed data7777><bulletin 2 flag field separator\lf>
<WMO header 2 for bulletin\cr\cr\lf>
<"GRIB"packed data7777><bulletin 3 flag field separator\lf>
.
.
.
<WMO header nn for bulletin\cr\cr\lf>
<"GRIB"packed data7777>

Octet Contents

The sections that follow list the contents of the GRIB2 bulletin, octet by octet.  When contents are described as "Missing," all bits are set to "1" in accordance with regulation 92.1.4.  When contents are described by a number, that number will be stored in the apprpriate octet.

Section 0--Indicator Section

 

Octet No.

Contents

1-4

"GRIB"

5-6

0

7

0 - for Meteorological Products, 10 - for Oceanographic Products

8

2

9-16

Total length of GRIB message in octets (including Section 0)

Section 1--Identification Section

In Section 1, octets 13-19 contain the reference time for the GRIB bulletin.  The NDFD is currently produced once an hour.  The reference time in Section 1 represents the day/hour of the current NDFD production cycle.
 

 

Octet No.

Contents

1-4

21

5

1

6-7

8

8-9

Missing

10

1

11

0 - Value will be used to designate the version number of the GRIB2-encoding software that produced the bulletin.  When changes to this published format occur, this version number will be updated.

12

1

13-14

Year (4 digits)

15

Month

16

Day

17

Hour

18

Minute

19

Second

20

0 or 1 - depending on the operational status of the encoded NDFD product (0 = operational, 1 = operational TEST)

21

1

Section 2--Local Use Section

Certain weather elements have provided particular challenges in encoding them in GRIB2.  Using Section 2 to encode various forms of metadata provides one solution.  For the NDFD elements Weather ("Wx"),  and Hazards, MDL GRIB2 encoding software uses the Local Use section for packing metadata unique to each grid.  At this time, for parameters other than Wx and Hazards, the Local Use section is omitted.

Grids of these 2 elements are stored as two distinct entities.  The first entity is a grid  of small integer values that will generally  store very compactly in Section  6.  The second entity is a series  of null-terminated strings of ASCII  characters called keys (either Wx or Hazard keys).    The integers on the weather grid serve  as indices, each pointing to one of the unique keys in the series.    Each key is comprised  of one or more subkeys, separated by  a caret "^".

The metadata packed in the Local Use Section for the Wx and Hazard elements is a lookup table.  The ASCII characters are loaded, one per octet, and then compressed using the Simple Packing Scheme for integers defined for Section 5.  The Simple Packing Scheme treats the set of keys as an integer array.  Each integer in the array is a decimal representation that corresponds to an ASCII character.  For instance, the integer 65 translates to the ASCII character "A".  The null character is represented by the integer 0, so that whenever a 0 is encountered in the array, it marks the ending of a unique key.  The tables that follow show the specific contents of the Weather keys/subkeys and Hazard keys/subkeys.
 

 

Octet No.

Contents

1-4

Length of section in octets (nn)

5

2

6

1 - Simple packing flag

7-nn

The Weather/Hazard keys needed to translate the contents the grid, packed using the Simple Packing scheme

Weather Keys and Subkeys

A weather subkey has can have up to five parts, each part separated by colons ":".
The parts are:

one weather type code.  See Weather Type Codes, below.

one coverage/probability code.  See Coverage/probability Codes, below.

one intensity code.  See Intensity Codes, below.

one visibility code.  See Visibility Codes, below.

  • zero or more attribute codes, separated by commas ",".   See Attribute Codes, below.

Weather Type Codes

 

Code

Meaning

Code

Meaning

<NoWx>

No Weather

T

Thunder

A

Hail

R

Rain

RW

Rain Showers

L

Drizzle

ZR

Freezing Rain

ZL

Freezing Drizzle

S

Snow

SW

Snow Showers

IP

Ice Pellets (sleet)

F

Fog

H

Haze

BS

Blowing Snow

K

Smoke

BD

Blowing Dust

FR

Frost

BN

Blowing Sand

IF

Ice Fog

IC

Ice Crystals

ZF

Freezing Fog

ZY

Freezing Spray

VA

Volcanic Ash

WP

Water Spouts

Coverage/probability Codes

 

Code

Meaning

Code

Meaning

<NoCov>

No Coverage/probability

Iso

Isolated

Sct

Scattered

Num

Numerous

Wide

Widespread

Ocnl

Occasional

SChc

Slight Chance

Chc

Chance

Lkly

Likely

Def

Definite

Patchy

Patchy

Areas

Areas of

Brf

Brief

Pds

Periods of

Frq

Frequent

Inter

Intermittent

Intensity Codes

 

Code

Meaning

Code

Meaning

<NoInten>

No Intensity

--

Very Light

-

Light

m

Moderate

+

Heavy

 

 

Visibility Codes

The following visibility codes may appear in WFO-generated GRIB2 bulletins.  The units are statute miles:  <NoVis>, 0SM, 1/4SM, 1/2SM, 3/4SM, 1SM, 11/2SM, 2SM, 21/2SM, 3SM, 4SM, 5SM, 6SM, P6SM.

Attribute Codes

 

Code

Meaning

Code

Meaning

FL

Frequent Lightning

GW

Gusty Winds

HvyRn

Heavy Rain

DmgW

Damaging Winds

SmA

Small Hail

LgA

Large Hail

OLA

on Outlying Areas

OBO

on Bridges and Overpasses

OGA

on Grassy Areas

OR

Or

Dry

Dry

Primary

Highest Ranking

Mention

Include Unconditionally

TOR

Tornado

Mx

Mixture

 

 

Size Limitations for NDFD National Grids

There is no (practical) limit to the number of weather keys, subkeys, etc.  For NDFD grids that are national mosaics of WFO-generated grids, the following limitations will be applied:

 

Item

Maximum number that will be present

Weather Attributes in a Weather Subkey

5

Weather Subkeys in a Weather Key

5

Weather Key Examples

 

Sample Weather Key

Meaning

Sct:SW:-:<NoVis>:

Light scattered snow showers

Ocnl:R:-:<NoVis>:^S:Ocnl:-:<NoVis>:^
SChc:ZR:-:<NoVis>:

Occasional light rain and snow, with a slight chance of light freezing rain

Wide:FR:-:<NoVis>:OLA

Widespread light frost in the outlying areas

<NoWx>:<NoCov>:<NoInten>:<NoVis>:

No weather

Sct:RW:-:<NoVis>:^T:Iso:m:<NoVis>:

Scattered light showers with isolated moderate thunderstorms

Sct:T:+:<NoVis>:DmgW,LgA

Scattered severe thunderstorms with damaging winds and large hail

Hazard Keys and Subkeys

A hazard key has two parts, separated by a  "."
The parts are:

  • a 2 letter phenomenon code.  This could be something like "HW" (for High Wind), or "SV" (for Severe Thunderstorm).
  • a 1 letter signifucance code.  This could be either "Y" (Advisory), "S" (Statement), "A" (Watch), or "W" (Warning).

A full list of Hazard keys found on NDFD grids can be found here.

Section 3--Grid Definition Section

Section 3 will vary depending upon the map projection the grid is defined.  A table listing more detailed information for each NDFD geographic region (CONUS, CONUS subsectors, Puerto Rico, Hawaii, Guam, Alaska) can be found here.  Latitude and longitude values are encoded in 10 -6 degrees.  All longitudes are east.

Lambert Conformal (includes CONUS and CONUS subsectors)

 

Octet No.

Contents

1-4

81 - Length of section in octets (nn)

5

3

6

0

7-10

Number of data points (Nx * Ny

11

0

12

0

13-14

30 - template number

15

1

16

0

17-20

6371200 - Radius of the earth

21

0

22-25

0

26

0

27-30

0

31-34

Nx - number of points along the X-axis.   (Click here to see Nx values for all Lambert Conformal NDFD grids)

35-38

Ny - number of points along the Y-axis   (Click here to see Ny values for all Lambert Conformal NDFD grids)

39-42

La1 - latitude of first grid point   (Click here to see La1 values for all Lambert Conformal NDFD grids)

43-46

Lo1 - longitude of first grid point   (Click here to see Lo1 values for all Lambert Conformal NDFD grids)

47

0

48-51

25,000,000 - Latitude where grid spacing is defined

52-55

265,000,000 - Orientation longitude

56-59

5,079,406 - Dx, X-direction grid length (Click here to see Dx values for Lambert Conformal NDFD grids)

60-63

5,079,406  - Dy, Y-direction grid length (Click here to see Dy values for Lambert Conformal NDFD grids)

64

0

65

80 - Scanning Mode

66-69

25,000,000 - Latin1, first secant latitude

70-73

25,000,000 - Latin2, second secant latitude

74-77

-90,000,000 - Latitude of southern pole 

78-81

0 - Longitude of southern pole

Polar Stereographic (Alaska)

 

Octet No.

Contents

1-4

65 - Length of section in octets (nn)

5

3

6

0

7-10

Number of data points (Nx * Ny)

11

0

12

0

13-14

20 - template number

15

1

16

0

17-20

6371200 - Radius of the earth

21

0

22-25

0

26

0

27-30

0

31-34

Nx - number of points along the X-axis   (Click here to see Nx values for all Polar Stereographic NDFD grids)

35-38

Ny - number of points along the Y-axis   (Click here to see Ny values for all Polar Stereographic NDFD grids)

39-42

La1 - latitude of first grid point   (Click here to see La1 values for all Polar Stereographic NDFD grids)

43-46

Lo1 - longitude of first grid point   (Click here to see Lo1 values for all Polar Stereographic NDFD grids)

47

0

48-51

60,000,000 - LaD, Latitude where mesh length defined

52-55

210,000,000 - LoV, Orientation longitude

56-59

5,953,125 - Dx, X-direction grid length

60-63

5,953,125 - Dy, Y-direction grid length

64

0 - Projection center flag

65

80 - Scanning mode

Mercator (includes Puerto Rico, Hawaii, and Guam)

 

Octet No.

Contents

1-4

72 - Length of section in octets (nn)

5

3

6

0

7-10

Number of data points   (Nx * Ny)

11

0

12

0

13-14

10 - template number

15

1

16

0

17-20

6371200 - Radius of the earth

21

0

22-25

0

26

0

27-30

0

31-34

Nx - number of points along the X-axis   (Click here to see Nx values for all Mercator NDFD grids)

35-38

Ny - number of points along the Y-axis   (Click here to see Ny values for all Mercator NDFD grids)

39-42

La1 - latitude of first grid point   (Click here to see La1 values for all Mercator NDFD grids)

43-46

Lo1 - longitude of first grid point   (Click here to see Lo1 values for all Mercator NDFD grids)

47

0

48-51

LaD - latitude where mesh length is defined   (Click here to see LaD values for all Mercator NDFD grids)

52-55

La2 - latitude of last gridpoint   (Click here to see La2 values for all Mercator NDFD grids)

56-59

Lo2 - longitude of last gridpoint   (Click here to see Lo2 values for all Mercator NDFD grids)

60

80 - Scanning mode

61-64

0.0000 - Orientation angle of the grid

65-68

2,500,000 - Di, longitudinal direction grid length - (Exception: Puerto Rico = 1,250,000)

69-72

2,500,000 - Dj, latitudinal direction grid length - (Exception: Puerto Rico = 1,250,000)

Section 4--Product Definition Section

Section 4 will vary from one weather element to the next.  The formats for the various elements are detailed in the following sections:

Maximum Temperature (MaxT), Minimum Temperature (MinT), Maximum Relative Humidity (MaxRH), Minimum Relative Humidity (MinRH)

 

Octet No.

Contents

1-4

58 - Length of section in octets (nn)

5

4

6-7

0

8-9

8

10

0

11

4 for MaxT 
5 for MinT

27 for MaxRH

198 for MinRH

12

2

13

0

14

0

15-16

255

17

Missing

18

1

19-22

Hours from reference time to beginning of the valid period. 

23

1

24

0

25-28

0

29

Missing

30

0

31-34

Missing

35-36

Year of end of the valid period in GMT.

37

Month of end of the valid period in GMT. 

38

Day of end of the valid period in GMT.

39

Hour of end of the valid period in GMT.

40

Minute of end of the valid period in GMT.

41

Second of end of the valid period in GMT.

42

1

43-46

0

47

2 for Max,  3 for Min

48

Missing

49

1

50-53

12

54

1

55-58

0

Twelve-hour Probability of Precipitation (PoP12)

 

Octet No.

Contents

1-4

71 - Length of section in octets (nn)

5

4

6-7

0

8-9

9

10

1

11

8

12

2

13

0

14

0

15-16

Missing

17

Missing

18

1

19-22

Hours from reference time to beginning of PoP12 valid period. 

23

1

24

0

25-28

0

29

Missing

30

Missing

31-34

Missing

35

Missing

36

Missing

37

1

38

Missing

39-42

Missing

43

3

44-47

254

48-49

Year of end of PoP12 valid period in GMT.

50

Month of end of PoP12 valid period in GMT.

51

Day of end of PoP12 valid period in GMT.

52

Hour of end of PoP12 valid period in GMT.

53

Minute of end of PoP12 valid period in GMT.

54

Second of end of PoP12 valid period in GMT.

55

1

56-59

0

60

1

61

Missing

62

1

63-66

12

67

1

68-71

0

Temperature, Dewpoint, Sky, Wind Speed, Wind Direction, Wave Height, Weather, Apparent Temperature, Relative Humidity, Wind Gust

 

Octet No.

Contents

1-4

34 - Length of section in octets (nn)

5

4

6-7

0

8-9

0

10

Parameter Category (FM 92 GRIB, Code Table 4.1) See table below for specific values

11

Parameter Number (FM 92 GRIB, Code Table 4.2) See table below for specific values

12

2

13

0

14

0

15-16

255

17

Missing

18

1

19-22

Forecast projection in hours

23

1

24

0

25-28

0

29

0

30

-1

31-34

Missing

Parameter Categories and Parameter Numbers for Temperature, Dewpoint, Sky, Wind Speed, Wind Direction, Wave Height, Weather, Apparent Temperature, Relative Humidity, Wind Gust

 

Parameter Name

Category

Number

Temperature

0

0

Dewpoint

0

6

Sky

6

1

Wind Speed

2

1

Wind Direction

2

0

Wave Height (see Note 1)

0

5

Weather

1

192

Apparent Temperature

0

193

Relative Humidity

1

1

Wind Gust

2

22

Note 1: Wave Height is defined as an Oceanographic Product in Section 0 (Indicator Section, octet 7 = 10).

QPF, Snow Amount, and Ice Accumulation

 

Octet No.

Contents

1-4

58 - Length of section in octets (nn)

5

4

6-7

0

8-9

8

10

1

11

8     for QPF
29   for Snow Amount 

227 for Ice Accumulation

12

2

13

0

14

0

15-16

255

17

Missing

18

1

19-22

Hours from reference time to beginning of valid period. 

23

1

24

0

25-28

0

29

Missing

30

-1

31-34

Missing

35-36

Year of end of valid period in GMT. 

37

Month of end of valid period in GMT.

38

Day of end of valid period in GMT.

39

Hour of end of valid period in GMT.

40

Minute of end of valid period in GMT.

41

Second of end of valid period in GMT. 

42

1

43-46

0

47

1

48

Missing

49

1

50-53

6

54

1

55-58

0

Tropical Wind Speed Probabilities (Incremental and Cumulative) greater than 34, 50, and 64 knots - from Tropical Prediction Center

Octet No.

Contents

1-4

71 - Length of section in octets (nn)

5

4

6-7

0

8-9

9

10

2 - Momentum

11

1 - Wind Speed

12

2

13

0

14

0

15-16

Missing

17

Missing

18

1

19-22

0

23

103 - specified height above ground level

24

0

25-28

10 (meters)

29

Missing

30

0

31-34

0

35

Missing

36

Missing

37

1 - probability of event above upper limit

38

0

39-42

0

43

3 - scale factor of upper limit

44-47

17491 (m/s), or 25722 (m/s), or 32924 (m/s) - corresponds to 34, 50, and 64 knots 

48-49

Year of end WindSpd Prob valid period in GMT

50

Month of end WindSpd Prob valid period in GMT

51

Day of end WindSpd Prob valid period in GMT

52

Hour of end WindSpd Prob valid period in GMT

53

Minute of end WindSpd Prob valid period in GMT

54

Second of end WindSpd Prob valid period in GMT

55

1

56-59

0

60

1

61

2 - (incremental probability), 192 - (cumulative probability)

62

1 - type of time increment between successive fields (hours)

63-66

6 - (incremental probability),  variable number of hours from the reference time to the end time of the valid period - cumulative probability)

67

1

68-71

0

Hazard Probabilities - from Storm Prediction Center (Includes Probabilities of Tornado, Hail, and Damaging Winds, Probabilities of Extreme Tornado, Hail, and Damaging Winds, Total Probability of Severe, and Extreme Severe Thunderstorms

Octet No.

Contents

1-4

71 - Length of section in octets (nn)

5

4

6-7

0

8-9

9

10

Parameter Category (FM 92 GRIB, Code Table 4.1) See table below for specific values

11

Parameter Number (FM 92 GRIB, Code Table 4.2) See table below for specific values

12

2

13

0

14

0

15-16

255

17

255

18

1

19-22

Hours from reference time to beginning of valid period

23

1

24

0

25-28

0

29

255

30

-1

31-34

-1

35

255

36

255

37

1

38

-1

39-42

-1

43

0

44-47

0

48-49

Year of end of valid period in GMT. 

50

Month of end of valid period in GMT.

51

Day of end of valid period in GMT.

52

Hour of end of valid period in GMT.

53

Minute of end of valid period in GMT.

54

Second of end of valid period in GMT. 

55

1

56-59

0

60

0

61

255

62

1

63-66

24

67

1

68-71

0

Parameter Categories and Parameter Numbers for Hazard Probabilities

Parameter Name

Parameter Category

Parameter No.

Probability of Tornado

19

197

Probability of Hail

19

198

Probability of Damaging Winds

19

199

Probability of Extreme Tornado

19

200

Probability of Extreme Hail

19

201

Probability of Extreme Damaging Winds

19

202

Total Probability of Severe Thunderstorms

19

203

Total Probability of Extreme Severe Thunderstorms

19

204

Categorical Outlooks - from Storm Prediction Center (Includes Convective Hazard Outlook, Fire Wx Critical and Extremely Critical Areas, and Fire Wx Critical Areas for Dry Thunderstorms)

Octet No.

Contents

1-4

58 - Length of section in octets

5

4

6-7

0

8-9

8

10

Parameter Category (FM 92 GRIB, Code Table 4.1) See table below for specific values

11

Parameter Number (FM 92 GRIB, Code Table 4.2) See table below for specific values

12

2

13

0

14

0

15-16

255

17

255

18

1

19-22

Hours from reference time to beginning of valid period

23

1

24

0

25-28

0

29

255

30

-1

31-34

-1

35-36

Year of end of valid period in GMT. 

37

Month of end of valid period in GMT.

38

Day of end of valid period in GMT.

39

Hour of end of valid period in GMT.

40

Minute of end of valid period in GMT.

41

Second of end of valid period in GMT. 

42

1

43-46

0

47

1

48

255

49

1

50-53

24

54

1

55-58

0

Parameter Categories and Parameter Numbers for Categorical Outlooks

Parameter Name

Parameter Category

Parameter No.

Convective Hazard Outlook

19

194

Fire Wx Critical and Extremely Critical Areas

192

192

Fire Wx Critical Areas for Dry Thunderstorms

192

194

 

Climate Outlook Probability Elements - from Climate Prediction Center (Average Temperature and Total Precip Above and Below Normal for 8-14 Day Outlook, 1 Month Outlook, and Seasonal Outlook)

Octet No.

Contents

1-4

71- Length of section in octets (nn)

5

4

6-7

0

8-9

9

10

Parameter Category (FM 92 GRIB, Code Table 4.1)    0 = Temperature, 1 = Moisture

11

Parameter Number (FM 92 GRIB, Code Table 4.2)     0 = Temperature, 8 = Total Precipitation

12

2

13

0

14

0

15-16

255

17

255

18

Indicator of unit of time range - 8-14 Day Outlooks = 2 (days); Monthly and Seasonal Outlooks = 3 (months)

19-22

Time from beginning of issuance day (8-14 Day Outlooks) or issuance month (Monthly/Seasonal Outlooks) to beginning of valid period in units specified by octet 18 

23

1

24

0

25-28

0

29

255

30

-1

31-34

-1

35

255

36

2 - Total Number of forecast probabilities

37

3 - Probability type

38

0

39-42

0

43

0

44-47

0

48-49

Year of end of valid period in GMT. 

50

Month of end of valid period in GMT.

51

Day of end of valid periodin GMT.

52

Hour of end of valid period in GMT.

53

Minute of end of valid period in GMT.

54

Second of end of valid period in GMT. 

55

1

56-59

0

60

0

61

255

62

Indicator of unit of time for time range over which statistical processing is done.   8-14 Day Outlooks = 2 (days); Monthly and Seasonal Outlooks = 3 (months)

63-66

Length of time range over which statistical processing is done.  8-14 Day Outlooks = 6 (days); Monthly Outlooks = 1 (month); Seasonal Outlooks = 3 (months)

67

1

68-71

0

Section 5--Data Representation Section

The GRIB2 standard supports eight forms of data packing.  Grids transmitted as part of the NDFD will use complex packing (Data Representation Template 5.2), and optionally, second order spatial differencing (Data Representation Template 5.3).

NDFD grids will generally contain a significant number of missing values.  National mosaic grids are defined to be rectangles, and they generally extend into areas where NWS WFOs do not have forecast responsibility.

 

Octet No.

Contents

1-4

47 or 49 - Length of section in octets (nn) (47 for Template 5.2, 49 for Template 5.3)

5

5

6-9

Total number of data points.

10-11

2 or 3

12-15

Reference value (R) as an IEEE 32-bit floating-point value.  Varies from grid to grid.

16-17

Binary scale factor (E).  Varies from weather element to weather element.  See Element Encoding Characteristics Table for values. For experimental fine resolution grids….click Here.

18-19

Decimal scale factor (D).  Varies from weather element to weather element.  See Element Encoding Characteristics Table for values. For experimental fine resolution grids….click Here.

20

Number of bits used for each group reference value.

21

1 (integer) for Weather grids; 0 (floating point) for all other weather elements.

22

1

23

1

24-27

Primary missing value substitute.  See Element Encoding Characteristics Table for values.  The values in the table will appear in the GRIB2 bulletins in Section 5, but will not appear with the data in section 7.  The GRIB2 standard calls for missing values to be carried as the largest value possible in a particular group. For experimental fine resolution grids….click Here

28-31

0

32-47

See GRIB2 documentation.

48

2 - Order of spatial differencing   (Template 5.3 only)

49

See GRIB2 documentation.   (Template 5.3 only)

Section 6--Bit-map Section

Bit-maps will not be used in NDFD GRIB bulletins.  Missing values will appear in those grid locations where forecasts are not valid.
 

 

Octet No.

Contents

1-4

6 - Length of section in octets (nn)

5

6

6

255

Section 7--Data Section

 

Octet No.

Contents

1-4

Length of section in octets (nn)

5

7

6-nn

See GRIB2 documentation.

Section 8--End Section

 

Octet No.

Contents

1-4

"7777"

 

NDFD Lambert Conformal CONUS Grid Spacing Values (Dx, DY)

 

Operational Values

Experimental Values

Dx

5,079,406

2,539,703

Dy

5,079,406

2,539,703

 

Element Encoding Characteristics

Weather Element

Original NDFD Units

GRIB2-encoded Units

Binary Scale Factor

Binary Scale Factor -

CONUS experimental fine resolution

Decimal Scale Factor

Decimal Scale Factor - CONUS experimental fine resolution

Primary Missing Value Substitute

MaxT

Fahrenheit

Kelvin

0

2

1

1

9999

MinT

Fahrenheit

Kelvin

0

2

1

1

9999

PoP12

Percent Probability

Percent Probability

0

0

0

0

9999

T

Fahrenheit

Kelvin

0

2

1

1

9999

Td

Fahrenheit

Kelvin

0

2

1

1

9999

Sky

Percentage
Total sky coverage

Percentage
Total sky coverage

0

0

0

0

9999

Wind Speed

Knots

ms-1

0

2

1

1

9999

Wind Direction

degrees true

Degrees true

0

0

0

-1

9999

Weather

N/A

N/A

0

0

0

0

9999

QPF

Inches

kgm-2

0

0

2

2

9999

Snow Amount

Inches

Meters

0

0

3

3

9999

Wave Height

Feet

Meters

0

0

1

1

9999

Apparent Temperature

Fahrenheit

Kelvin

0

2

1

1

9999

Relative Humidity

Percent

Percent

0

0

0

0

9999

Wind Gust

Knots

ms-1

0

2

1

1

9999

Tropical Wind Speed Probabilities 
(34, 50, 65 kts)
Cumulative and Incremental

Percent Probability

Percent Probability

0

0

0

0

9999

Convective Outlooks/Fire Wx Outlooks

Categorical

Categorical

0

0

0

0

9999

Hazard Probabilities

Percent Probability

Percent Probability

0

0

0

0

9999

Climate Outlook Probabilities

Categorical

Categorical

0

0

0

0

9999

Ice Accumulation

Inches

kgm-2

0

0

2

2

9999

MaxRH

%

%

0

0

0

0

9999

MinRH

%

%

0

0

0

0

9999


 

NDFD Grid Location and Sizes (by geographic region/sector)

Lambert Conformal

Sector Name

Item

Value

CONUS

 

 

 

Nx

1073

 

Ny

689

 

La1

2019199

 

Lo1

2384459

CONUS - experimental fine resolution

 

 

Nx

2143

 

Ny

1375

 

La1

2019199

 

Lo1

2384459

Central Great Lakes

 

 

 

Nx

173

 

Ny

219

 

La1

3876136

 

Lo1

2715378

Central Mississippi Valley

 

 

 

Nx

197

 

Ny

187

 

La1

3409910

 

Lo1

2646187

Central Plains

 

 

 

Nx

223

 

Ny

187

 

La1

3469884

 

Lo1

2550276

Central Rockies

 

 

 

Nx

254

 

Ny

185

 

La1

3510457

 

Lo1

2462040

Eastern Great Lakes

 

 

 

Nx

187

 

Ny

192

 

La1

3925241

 

Lo1

2735126

Mid-Atlantic

 

 

 

Nx

194

 

Ny

200

 

La1

3139028

 

Lo1

2742057

Northeast

 

 

 

Nx

187

 

Ny

229

 

La1

3869834

 

Lo1

2812826

Northern Plains

 

 

 

Nx

252

 

Ny

239

 

La1

3968270

 

Lo1

2546129

Northern Rockies

 

 

 

Nx

306

 

Ny

228

 

La1

3944028

 

Lo1

2439814

Pacific Northwest

 

 

 

Nx

313

 

Ny

212

 

La1

3949451

 

Lo1

2341168

Pacific Southwest

 

 

 

Nx

312

 

Ny

252

 

La1

2926025

 

Lo1

2368744

Southeast

 

 

 

Nx

243

 

Ny

201

 

La1

2407851

 

Lo1

2691026

Southern Mississippi Valley

 

 

 

Nx

199

 

Ny

184

 

La1

2860611

 

Lo1

2640133

Southern Plains

 

 

 

Nx

314

 

Ny

275

 

La1

2510639

 

Lo1

2528770

Southern Rockies

 

 

 

Nx

267

 

Ny

190

 

La1

3031159

 

Lo1

2451204

Upper Mississippi Valley

 

 

 

Nx

245

 

Ny

270

 

La1

3818489

 

Lo1

2597956

Polar Stereographic

Sector Name

Item

Value

Alaska

 

 

 

Nx

825

 

Ny

553

 

La1

4053010

 

Lo1

1814290

Mercator

Sector Name

Item

Value

Puerto Rico

 

 

 

Nx

339

 

Ny

227

 

La1

1697739

 

Lo1

2919721

 

La2

195445

 

Lo2

296016

 

LaD

2000000

Hawaii

 

 

 

Nx

321

 

Ny

225

 

La1

180726

 

Lo1

1984750

 

La2

230877

 

Lo2

206131

 

LaD

2000000

Guam

 

 

 

Nx

193

 

Ny

193

 

La1

1234988

 

Lo1

1436865

 

La2

1679439

 

Lo2

1482800

 

LaD

2000000

NDFD Hazard Keys
 

Code

Phenomenon/Significance

Code

Phenomenon/Significance

Code

Phenomenon/Significance

Code

Phenomenon/Significance

AF.W

AshFall Warning

GL.A

Gale Watch

<None>

No Hazard

WC.W

Wind Chill Warning

AF.Y

AshFall Advisory

GL.W

Gale Warning

RB.Y

Small Craft Advisory for Rough Bar

WC.Y

Wind Chill Advisory

AS.Y

Air Stagnation Advisory

HF.A

Hurricane Force Wind Watch

SB.Y

Snow and Blowing Snow Advisory

WI.Y

Wind Advisory

BS.Y

Blowing Snow Advisory

HF.W

Hurricane Force Wind Warning

SC.Y

Small Craft Advisory

WS.A

Winter Storm Watch

BW.Y

Brisk Wind Advisory

HI.A

Hurricane Wind Watch

SE.A

Hazardous Seas Watch

WS.W

Winter Storm Warning

BZ.A

Blizzard Watch

HI.W

Hurricane Wind Warning

SE.W

Hazardous Seas Warning

WW.Y

Winter Weather Advisory

BZ.W

Blizzard Warning

HS.W

Heavy Snow Warning

SI.Y

Small Craft Advisory for Winds

ZF.Y

Freezing Fog Advisory

CF.A

Coastal Flood Watch

HT.Y

Heat Advisory

SM.Y

Dense Smoke Advisory

ZR.Y

Freezing Rain Advisory

CF.S

Coastal Flood Statement

HU.A

Hurricane Watch

SN.Y

Snow Advisory

ZY.Y

Freezing Spray Advisory

CF.W

Coastal Flood Warning

HU.S

Hurricane Statement

SR.A

Storm Watch

 

 

CF.Y

Coastal Flood Advisory

HU.W

Hurricane Warning

SR.W

Storm Warning

 

 

DS.W

Dust Storm Warning

HW.A

High Wind Watch

SU.W

High Surf Warning

 

 

DU.Y

Blowing Dust Advisory

HW.W

High Wind Warning

SU.Y

High Surf Advisory

 

 

EC.A

Extreme Cold Watch

HZ.A

Hard Freeze Watch

SV.A

Severe Thunderstorm Watch

 

 

EC.W

Extreme Cold Warning

HZ.W

Hard Freeze Warning

SV.W

Severe Thunderstorm Warning

 

 

EH.A

Excessive Heat Watch

IP.W

Sleet Warning

SW.Y

Small Craft Advisory for Hazardous Seas

 

 

EH.W

Excessive Heat Warning

IP.Y

Sleet Advisory

TI.A

Tropical Storm Wind Watch

 

 

EW.W

Extreme Wind Warning

IS.W

Ice Storm Warning

TI.W

Tropical Storm Wind Warning

 

 

FA.A

Areal Flood Watch

LB.Y

Lake Effect Snow and Blowing Snow Advis.

TO.A

Tornado Watch

 

 

FA.W

Areal Flood Warning

LE.A

Lake Effect Snow Watch

TO.W

Tornado Warning

 

 

FA.Y

Areal Flood Advisory

LE.W

Lake Effect Snow Warning

TR.A

Tropical Storm Watch

 

 

FF.A

Flash Flood Watch

LE.Y

Lake Effect Snow Advisory

TR.S

Tropical Storm Advisory

 

 

FF.W

Flash Flood Warning

LO.Y

Low Water Advisory

TR.W

Tropical Storm Warning

 

 

FG.Y

Dense Fog Advisory

LS.A

Lake Shore Flood Watch

TS.A

Tsunami Watch

 

 

FL.A

Flood Watch

LS.S

Lake Shore Flood Statement

TS.W

Tsunami Warning

 

 

FL.W

Flood Warning

LS.W

Lake Shore Flood Warning

TS.Y

Tsunami Advisory

 

 

FL.Y

Flood Advisory

LS.Y

Lake Shore Flood Advisory

TY.A

Typhoon Watch

 

 

FR.Y

Frost Advisory

LW.Y

Lake Wind Advisory

TY.S

Typhoon Statement

 

 

FW.A

Fire Weather Watch

MA.S

Marine Weather Statement

TY.W

Typhoon Warning

 

 

FW.W

Fire Weather Warning

MA.W

Marine Weather Warning

UP.A

Heavy Freezing Spray Watch

 

 

FZ.A

Freeze Watch

MF.Y

Dense Fog Advisory

UP.W

Heavy Freezing Spray Warning

 

 

FZ.W

Freeze Warning

MH.Y

AshFall Advisory

UP.Y

Heavy Freezing Spray Advisory

 

 

 

 

MS.Y

Dense Smoke Advisory

WC.A

Wind Chill Watch