NOAA’s NOAA’s National Weather Service National Weather Service Tools To Access the NDFD Tools To Access the NDFD Arthur Taylor Arthur Taylor RS Information Systems / Meteorological Development Laboratory RS Information Systems / Meteorological Development Laboratory National Digital Forecast Database Technical Workshop National Digital Forecast Database Technical Workshop August 13, 2003 August 13, 2003
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NOAA’s National Weather Service Tools To Access the NDFD
NOAA’s National Weather Service Tools To Access the NDFD. Arthur Taylor RS Information Systems / Meteorological Development Laboratory National Digital Forecast Database Technical Workshop August 13, 2003. NDFD: How do I use it?. - PowerPoint PPT Presentation
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NOAA’s NOAA’s National Weather ServiceNational Weather ServiceTools To Access the NDFDTools To Access the NDFD
Arthur TaylorArthur TaylorRS Information Systems / Meteorological Development Laboratory RS Information Systems / Meteorological Development Laboratory
National Digital Forecast Database Technical WorkshopNational Digital Forecast Database Technical Workshop
• Since NDFD uses the WMO’s GRIB2 format, which is relatively Since NDFD uses the WMO’s GRIB2 format, which is relatively new, NWS is providing a decoder library. The current versions new, NWS is providing a decoder library. The current versions of the library are located at:of the library are located at:– http://www.nws.noaa.gov/mdl/iwt/grib2/decoder.htmhttp://www.nws.noaa.gov/mdl/iwt/grib2/decoder.htm
• In addition, NWS is providing a driver “degrib” (aka In addition, NWS is providing a driver “degrib” (aka “NDFD_GRIB2Decoder”) for the library. Degrib’s primary “NDFD_GRIB2Decoder”) for the library. Degrib’s primary purposes are:purposes are:– Allow users to convert GRIB2 to other formats for use with various Allow users to convert GRIB2 to other formats for use with various
Geographic Information Systems (GIS), without need for a programmer.Geographic Information Systems (GIS), without need for a programmer.
– Provide an example of how to call the decoder librariesProvide an example of how to call the decoder libraries
– Enable some form of access to the data without requiring other packagesEnable some form of access to the data without requiring other packages• Generate ImagesGenerate Images
• Probe a give lat / lon location for all the relevant dataProbe a give lat / lon location for all the relevant data
•Degrib can be downloaded from:Degrib can be downloaded from:– http://www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder/register.htmhttp://www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder/register.htm
• On the download page, MS-Windows users should get “ndfd-On the download page, MS-Windows users should get “ndfd-demo.exe”, which contains:demo.exe”, which contains:
• An installation wizardAn installation wizard
• Compiled codeCompiled code
• Source code for the libraries, and the “degrib” and “tkdegrib” programs Source code for the libraries, and the “degrib” and “tkdegrib” programs (superImageGen and htmlmaker source code are not provided)(superImageGen and htmlmaker source code are not provided)
• DocumentationDocumentation
• Unix users should get “degrib-unix.tar.gz”, which contains:Unix users should get “degrib-unix.tar.gz”, which contains:• Source code for the libraries and the “degrib” and “tkdegrib” programsSource code for the libraries and the “degrib” and “tkdegrib” programs
• Documentation.Documentation.
• To compile the code you need: To compile the code you need: • FORTRAN (g77 should work) : for the decoder libraryFORTRAN (g77 should work) : for the decoder library
• C (gcc should work) : for the “drivers” and projection libraryC (gcc should work) : for the “drivers” and projection library
• Optional : Tcl/Tk (free from Optional : Tcl/Tk (free from http://scriptics.comhttp://scriptics.com) : for the Graphical User Interface) : for the Graphical User Interface
Step 1: Download some data.Step 1: Download some data.• The GUI version of degrib, The GUI version of degrib,
“tkdegrib”, provides a “tkdegrib”, provides a convenient interface to get convenient interface to get NDFD either via ftp or http.NDFD either via ftp or http.– Highlight the desired sectorHighlight the desired sector
– Click on either “Download by ftp” Click on either “Download by ftp” or “Download by http”or “Download by http”
• Alternatively, you can use Alternatively, you can use various UNIX tools to get the various UNIX tools to get the data directly from:data directly from:– http://weather.noaa.gov/pub/SL.uhttp://weather.noaa.gov/pub/SL.u
Currently degrib can convert Currently degrib can convert to the following formats:to the following formats:• ESRI Point .shp filesESRI Point .shp files
• .flt files for use with ESRI .flt files for use with ESRI Spatial AnalystSpatial Analyst
• .flt files for use with other .flt files for use with other programs that can read NxM programs that can read NxM 4 byte floats.4 byte floats.
In addition, degrib creates In addition, degrib creates a .txt file which contains the a .txt file which contains the meta data that was in the meta data that was in the GRIB2 message.GRIB2 message.
Degrib: Convert to .shp fileDegrib: Convert to .shp file
To convert to .shp format:To convert to .shp format:– Double click on the GRIB2 file Double click on the GRIB2 file
(top pane)(top pane)
– Select message to convert Select message to convert (middle pane)(middle pane)
– Choose an “output file name”Choose an “output file name”
– Click on “Generate .shp files”Click on “Generate .shp files”
• ““Polygon .shp” creates Polygon .shp” creates better images in ESRI and is better images in ESRI and is easier to manipulate, but it is easier to manipulate, but it is larger than the “Point .shp”larger than the “Point .shp”
• ““Include Missing Values” Include Missing Values” allows you to study the allows you to study the entire grid, or limit the result entire grid, or limit the result to where data existsto where data exists
Degrib: Convert to .flt fileDegrib: Convert to .flt file
To convert to .flt file (for use To convert to .flt file (for use with GrADS or ESRI Spatial with GrADS or ESRI Spatial Analyst):Analyst):
– Double click on the GRIB2 file Double click on the GRIB2 file (top pane)(top pane)
– Select message to convert Select message to convert (middle pane)(middle pane)
– Choose an “output file name”Choose an “output file name”– Click on “Generate .flt files”Click on “Generate .flt files”
• ““GrADS .ctl file”: creates a GrADS .ctl file”: creates a control file which GrADS can control file which GrADS can use to access the .flt fileuse to access the .flt file
• ““Interpolate”: bi-linear Interpolate”: bi-linear interpolates to a lat / lon interpolates to a lat / lon coverage grid.coverage grid.
• ““M.S.B. first”: creates the .flt M.S.B. first”: creates the .flt files in “Big Endian” format.files in “Big Endian” format.
To encode Weather (Wx), NDFD disseminates “ugly To encode Weather (Wx), NDFD disseminates “ugly strings”.strings”.• Advantage: A flexible format that can encode a description of Advantage: A flexible format that can encode a description of
weather such as “Chance of thunderstorms and chance of weather such as “Chance of thunderstorms and chance of heavy rain showers”heavy rain showers”
Difficulty: An “ugly string” is not a number, so it is Difficulty: An “ugly string” is not a number, so it is challenging to store in GRIB2.challenging to store in GRIB2.• Solution: Use GRIB2 section 2 to provide an ASCII look up table, Solution: Use GRIB2 section 2 to provide an ASCII look up table,
and store the numeric values in the regular GRIB2and store the numeric values in the regular GRIB2– Note: each weather grid, for each forecast projection, has a different Note: each weather grid, for each forecast projection, has a different
ASCII look up table, so without section 2 it has no meaning.ASCII look up table, so without section 2 it has no meaning.
• Some Questions:Some Questions:– What does “Chc:T:<NoInten>:<NoVis>:^Chc:RW:+:<NoVis>:” mean, and What does “Chc:T:<NoInten>:<NoVis>:^Chc:RW:+:<NoVis>:” mean, and
how, for example, is an Emergency Manager supposed to know that?how, for example, is an Emergency Manager supposed to know that?– What can be done for the .flt file? What can be done for the .flt file?
Degrib looks up the value, and parses it Degrib looks up the value, and parses it when it saves Wx to a .shp filewhen it saves Wx to a .shp file• Wx-Index: Ugly string index used in the Wx-Index: Ugly string index used in the
GRIB2 message.GRIB2 message.• Visibility: The lowest visibility in the 5 Visibility: The lowest visibility in the 5
“ugly string words” (in statute miles).“ugly string words” (in statute miles).• NDFD wxCode: An encoding of the ugly NDFD wxCode: An encoding of the ugly
string using the first wx-type, intensity, and string using the first wx-type, intensity, and coverage, and the second wx-type.coverage, and the second wx-type.
• Weather 1: English translation of the “ugly Weather 1: English translation of the “ugly word”word”
• Wx-Inten 1: A number code for the wx-type Wx-Inten 1: A number code for the wx-type and wx-intensityand wx-intensity
• Cover 1: A number code for the coverageCover 1: A number code for the coverage• Hazard 1: A number code for hazards.Hazard 1: A number code for hazards.
– There can be 5 hazards per word, there are 9 There can be 5 hazards per word, there are 9 types of hazards. So each hazard is given a types of hazards. So each hazard is given a digit, the digits are sorted. Result: “00045” = 45 digit, the digits are sorted. Result: “00045” = 45 for “Damaging Wind (4) and “Small Hail (5)”for “Damaging Wind (4) and “Small Hail (5)”
Example: Weather in ArcViewExample: Weather in ArcView
In “/degrib/ArcView/”, In “/degrib/ArcView/”, there is a weather.avl there is a weather.avl which was applied to which was applied to the “Wx-Inten 1” to the “Wx-Inten 1” to create this image.create this image.• Problem: Chance of Problem: Chance of
thunderstorms (T), thunderstorms (T), and severe T have the and severe T have the same color.same color.
• Intent: get people Intent: get people started.started.
• If you have a If you have a better .avl, and want better .avl, and want to share, let me know.to share, let me know.
For CONUS (continental U.S.), NDFD uses a Lambert Conformal For CONUS (continental U.S.), NDFD uses a Lambert Conformal Conic Map Projection:Conic Map Projection:• Tangent latitutude 25, orientation longitude -95, mesh latitude 25, mesh Tangent latitutude 25, orientation longitude -95, mesh latitude 25, mesh
size 5079.406 m.size 5079.406 m.
• In ESRI ArcMap that would be:In ESRI ArcMap that would be:– 1st Parallel = 21st Parallel = 2ndnd Parallel = 25 degrees north (tangent latitude) Parallel = 25 degrees north (tangent latitude)
– Lon of center of projection = -95 degrees (orientation longitude) Lon of center of projection = -95 degrees (orientation longitude)
– Lat of center of projection = 25 degrees (tangent latitude) Lat of center of projection = 25 degrees (tangent latitude)
– False easting = 0 m, False northing = 0 m, X Shift = 0, Y Shift = 0 False easting = 0 m, False northing = 0 m, X Shift = 0, Y Shift = 0
In addition, NDFD uses a spherical earth with radius 6371.2 kmIn addition, NDFD uses a spherical earth with radius 6371.2 km– Note: 6367.47 km is currently in the GRIB2 messages, but NDFD used the same Note: 6367.47 km is currently in the GRIB2 messages, but NDFD used the same
methods that NCEP used, which depended on the 6371.2 km sphere.methods that NCEP used, which depended on the 6371.2 km sphere.
To assist ESRI ArcView 3.x, degrib creates a .ave (ArcView Avenue To assist ESRI ArcView 3.x, degrib creates a .ave (ArcView Avenue script) to set the projection and radius correctly.script) to set the projection and radius correctly.
This is for people who know their lat/lon and just want This is for people who know their lat/lon and just want text output. To probe a point from a command prompt text output. To probe a point from a command prompt (not available yet in “tkdegrib”) :(not available yet in “tkdegrib”) :
• The first example probes just 1 point, while the second reads a The first example probes just 1 point, while the second reads a file which is of the form: Station ID, lat, lon per line. The second file which is of the form: Station ID, lat, lon per line. The second form allows for numerous stations.form allows for numerous stations.
• By default, probe chooses the “nearest” grid cell, but using the By default, probe chooses the “nearest” grid cell, but using the “-Interp” option, causes it to perform bi-linear interpolation.“-Interp” option, causes it to perform bi-linear interpolation.
Everything previously discussed can be done using Everything previously discussed can be done using degrib, except data download, so the degrib step can degrib, except data download, so the degrib step can be automated. See (./degrib1.2/docs/degrib.txt for help)be automated. See (./degrib1.2/docs/degrib.txt for help)
Maintain the program by keeping up with NDFD as more Maintain the program by keeping up with NDFD as more variables / sectors are introduced.variables / sectors are introduced.
– In order to inform users of updates, degrib has an “announcement mailing In order to inform users of updates, degrib has an “announcement mailing list”, which currently has 119 people on it.list”, which currently has 119 people on it.
Improvements: Based on user feedback, current Improvements: Based on user feedback, current thoughts are:thoughts are:
– Create merged polygons. Instead of a polygon per cell, join similar Create merged polygons. Instead of a polygon per cell, join similar values together to form large polygons.values together to form large polygons.
– Create some form of graphical probe point capabilityCreate some form of graphical probe point capability– Create some form of un-compressed database so that a CGI callable Create some form of un-compressed database so that a CGI callable
probe program can be used to access the data quicklyprobe program can be used to access the data quickly– Add some way for UNIX users (without GrADS) to plot the imagesAdd some way for UNIX users (without GrADS) to plot the images– Add some way for users to zoom in on a mapAdd some way for users to zoom in on a map– Interface to more file formatsInterface to more file formats