noaa’s national weather service ndfd dissemination services allan darling office of the cio,...

NOAA’sNOAA’sNational Weather ServiceNational Weather ServiceNDFD Dissemination ServicesNDFD Dissemination Services

Allan DarlingAllan Darling

Office of the CIO, Telecommunication Operations CenterOffice of the CIO, Telecommunication Operations Center

National Digital Forecast Database Technical WorkshopNational Digital Forecast Database Technical Workshop

August 13, 2003August 13, 2003

NDFD Technical Workshop 2003NDFD Technical Workshop 2003

NDFD Dissemination ServicesNDFD Dissemination Services

What will we cover?

• Where to find NDFD product files

• Information about the servers where the data is stored

• How files are named

• How files are constructed

• How product headings are formed

• What a “super heading” is

•Where to go for more information



Where to find NDFD product files –

Files are available via:

ftp://tgftp.nws.noaa.gov

http://weather.noaa.gov/pub

ftp://ptgftp.nws.noaa.gov

(Access to ptgftp.nws.noaa.gov is limited to SAS customers - see http://weather.gov/datamgmt/fos/fospage.html for more information about Server Access Services.



About the servers –

All servers are classed a operational systems with 24x7 support and monitoring

tgftp.nws.noaa.gov – Cluster of five public anonymous FTP servers

weather.noaa.gov – Cluster of five public HTTP servers

ptgftp.nws.noaa.gov – Cluster of two restricted access anonymous FTP servers



Where to find NDFD product files –

On each server, NDFD data is found under the path:

/SL.us008001/ST.expr/DF.gr2/DC.ndfd/...

The path indicates that the data is on the public NWSTG FTP server, is experimental, is encoded in WMO GRIB Edition 2 format, and is all related to the NDFD data category.See http://www.nws.noaa.gov/datamgmt/filstnd.html for more information about the directory and file naming standards used on the NWSTG FTP and HTTP Servers



How files are named –

Following the data format and category directories, the last directory and the file name specify:

• the geographic area (/AR.aaaaaaaa)

• the data subcategory (/ds.sssss)

A list of all the NDFD Sectors (geographic areas) and the data subcategories is available at http://www.nws.noaa.gov/datamgmt/doc/ndfdelem.xls This spreadsheet also defines the NDFD sectors by Lat/Lon and grid points



How files are named –

The file

ftp://tgftp.nws.noaa.gov/SL.us008001/ST.expr/DF.gr2/DC.ndfd/AR.midatlan/ds.maxt.bin

contains the daytime maximum temperature for the Mid-Atlantic sector.



How files are constructed –

Files are comprised of:

• A flag field separator block (option 2)

• A super heading

• One or more GRIB products each comprised of• A flag field separator block (option 2)

• A WMO Heading

• A GRIB product



How files are constructed –

A flag field separator block (option 2) is a file delimiter that provides the length of the product that follows it. The format is:

****nnnnnnnnnn****lf

Where nnnnnnnnnn is the length of the product following the seperator, in bytes and lf is an ASCII line feed. See http://weather.gov/tg/fstandrd.html for more details.



How files are constructed –****0000149136****YGCZ99 KWBN 031906****0000018449****YGCB00 KWBN 031906GRIB..................7777****0000018847****YGCC00 KWBN 031906GRIB.....................7777...****0000018051****YGCI00 KWBN 031906GRIB.................7777



How product headings are formed –

Generic WMO Heading: T1T2A1A2ii CCCC

Generic NDFD Heading: YT2A1A2ii KWBN

T2 specified the data type (data subcategory)

A1 specifies the geographic designator (NDFD sector)

A2 and ii together specify the NDFD reference time (not represented in the directory or file names)




Generic NDFD Heading: YT2A1A2ii KWBN

The possible values for T2 , A1 , A2 , and ii and their meanings are specified on the NDFD WMO Heading Reference page at

http://weather.gov/datamgmt/doc/ndfdref.html



A = SKY COVER

B = WIND DIRECTION

C = WIND SPEED

D = PROBABILITY OF PRECIPITATION (12 HOURS)

E = SURFACE TEMPERATURE

F = DEWPOINT TEMPERATURE

G = DAYTIME MAXIMUM TEMPERATURE

H = NIGHTTIME MINIMUM TEMPERATURE

I = QUANTITATIVE PRECIPITATION

J = WEATHER

K = WAVE HEIGHT

S = SNOWFALL AMOUNT

U = FREE AIR WIND DIRECTION

V = FREE AIR WIND SPEED


T2 – data type



****0000149136****YGCZ99 KWBN 031906****0000018449****YGCB00 KWBN 031906GRIB..................7777****0000018847****YGCC00 KWBN 031906GRIB.....................7777...****0000018051****YGCI00 KWBN 031906GRIB.................7777

YGCB00 KWBN

Y -NDFD ProductG – Daytime Maximum TemperatureC – Mid-Atlantic SectorB – Day 100 – Hour 0

Decoding a product heading -



What is a “super heading”?

In order to aggregate all of the forecast periods for one data subcategory and one sector, the “super heading” was developed.

The super heading specifies the data subcategory in T2 and the geographic sector in A1. A2 and ii are fixed as “Z99”:

NDFD Super Heading: YT2A1Z99 KWBN




YGCZ99 KWBN

Y -NDFD ProductG – Daytime Maximum TemperatureC – Mid-Atlantic SectorZ99 – Super Heading

The super heading contains one or more instances of a flag field separator, WMO heading and GRIB product.

What is a “super heading”?




****0000149136****YGCZ99 KWBN 031906

149136 is the length, in bytes, of the super heading and all the following groups of flag field separators, WMO headings, and GRIB products.

Super heading flag field separator -




****0000018449****YGCB00 KWBN 031906GRIB.............7777

18449 is the length, in bytes, of the single heading and GRIB product.

“Regular” flag field separator -



For more dissemination information –

NWSTG Data Management NDFD Reference - http://weather.gov/datamgmt/doc/ndfdindex.html

Directory and File Naming Standards –

http://weather.gov/datamgmt/filstnd.html

Family of Services Main Page –

http://weather.gov/datamgmt/fos/fosindex.html

Gateway File Standards and Content Structures –

http://weather.gov/tg/fstandrd.html

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