NOAA

1
NOAAs National Weather ServiceTools To Access
the NDFD

• Arthur TaylorRS Information Systems /
  Meteorological Development Laboratory
• National Digital Forecast Database Technical
  Workshop
• August 13, 2003

2
NDFD How do I use it?

• Since NDFD uses the WMOs GRIB2 format, which is
  relatively new, NWS is providing a decoder
  library. The current versions of the library are
  located at
• http//www.nws.noaa.gov/mdl/iwt/grib2/decoder.htm
• http//www.nws.noaa.gov/mdl/iwt/grib2/encoder.htm
• In addition, NWS is providing a driver degrib
  (aka NDFD_GRIB2Decoder) for the library.
  Degribs primary purposes are
• Allow users to convert GRIB2 to other formats for
  use with various Geographic Information Systems
  (GIS), without need for a programmer.
• Provide an example of how to call the decoder
  libraries
• Enable some form of access to the data without
  requiring other packages
• Generate Images
• Probe a give lat / lon location for all the
  relevant data

3
Degrib Installation

• Degrib can be downloaded from
• http//www.nws.noaa.gov/mdl/NDFD_GRIB2Decoder/regi
  ster.htm
• On the download page, MS-Windows users should get
  ndfd-demo.exe, which contains
• An installation wizard
• Compiled code
• Source code for the libraries, and the degrib
  and tkdegrib programs (superImageGen and
  htmlmaker source code are not provided)
• Documentation
• Unix users should get degrib-unix.tar.gz, which
  contains
• Source code for the libraries and the degrib
  and tkdegrib programs
• Documentation.
• To compile the code you need
• FORTRAN (g77 should work) for the decoder
  library
• C (gcc should work) for the drivers and
  projection library
• Optional Tcl/Tk (free from http//scriptics.com)
  for the Graphical User Interface

4
Degrib Data download

• Step 1 Download some data.
• The GUI version of degrib, tkdegrib, provides a
  convenient interface to get NDFD either via ftp
  or http.
• Highlight the desired sector
• Click on either Download by ftp or Download by
  http
• Alternatively, you can use various UNIX tools to
  get the data directly from
• http//weather.noaa.gov/pub/SL.us008001/ST.expr/DF
  .gr2/DC.ndfd/
• ftp//tgftp.nws.noaa.gov/SL.us008001/ST.expr/DF.gr
  2/DC.ndfd/

5
Degrib Convert

• Currently degrib can convert to the following
  formats
• ESRI Point .shp files
• ESRI Polygons .shp files
• GrADS lat / lon grids
• GrADS Projected grids
• .flt files for use with ESRI Spatial Analyst
• .flt files for use with other programs that can
  read NxM 4 byte floats.
• In addition, degrib creates a .txt file which
  contains the meta data that was in the GRIB2
  message.

6
Degrib Convert to .shp file

• To convert to .shp format
• Double click on the GRIB2 file (top pane)
• Select message to convert (middle pane)
• Choose an output file name
• Click on Generate .shp files
• Polygon .shp creates better images in ESRI and
  is easier to manipulate, but it is larger than
  the Point .shp
• Include Missing Values allows you to study the
  entire grid, or limit the result to where data
  exists

7
CONUS MaxT in ArcView
8
Polygon vs Point, DC area
9
Degrib Convert to .flt file

• To convert to .flt file (for use with GrADS or
  ESRI Spatial Analyst)
• Double click on the GRIB2 file (top pane)
• Select message to convert (middle pane)
• Choose an output file name
• Click on Generate .flt files
• GrADS .ctl file creates a control file which
  GrADS can use to access the .flt file
• Interpolate bi-linear interpolates to a lat /
  lon coverage grid.
• M.S.B. first creates the .flt files in Big
  Endian format.

10
CONUS MaxT in GrADS
11
NDFD, GRIB2 Weather

• To encode Weather (Wx), NDFD disseminates ugly
  strings.
• Advantage A flexible format that can encode a
  description of weather such as Chance of
  thunderstorms and chance of heavy rain showers
• Difficulty An ugly string is not a number, so
  it is challenging to store in GRIB2.
• Solution Use GRIB2 section 2 to provide an ASCII
  look up table, and store the numeric values in
  the regular GRIB2
• Note each weather grid, for each forecast
  projection, has a different ASCII look up table,
  so without section 2 it has no meaning.
• Some Questions
• What does ChcTltNoIntengtltNoVisgtChcRWltNoVi
  sgt mean, and how, for example, is an Emergency
  Manager supposed to know that?
• What can be done for the .flt file?

12
Weather .shp files

• Degrib looks up the value, and parses it when it
  saves Wx to a .shp file
• Wx-Index Ugly string index used in the GRIB2
  message.
• Visibility The lowest visibility in the 5 ugly
  string words (in statute miles).
• NDFD wxCode An encoding of the ugly string using
  the first wx-type, intensity, and coverage, and
  the second wx-type.
• Weather 1 English translation of the ugly word
• Wx-Inten 1 A number code for the wx-type and
  wx-intensity
• Cover 1 A number code for the coverage
• Hazard 1 A number code for hazards.
• There can be 5 hazards per word, there are 9
  types of hazards. So each hazard is given a
  digit, the digits are sorted. Result 00045
  45 for Damaging Wind (4) and Small Hail (5)

13
Weather Codes
Coverage Table
0 No Coverage
1 Isolated
2 Scattered
3 Numerous
4 Widespread
5 Occasional
6 Slight Chance of
7 Chance of
8 Likely
9 Definite
10 Patchy
11 Areas of
Wx-Inten Table
0 No Weather
1-5 Smoke (no Intensity, very light, light, moderate, heavy)
6-10 Blowing Dust (no Intensity, very light, light, moderate, heavy)
11-15 Blowing Snow (no Intensity, very light, light, moderate, heavy)
16-20 Haze (no Intensity, very light, light, moderate, heavy)
21-25 Fog (no Intensity, very light, light, moderate, heavy)
26-30 Drizzle (no Intensity, very light, light, moderate, heavy)
31-35 Rain (no Intensity, very light, light, moderate, heavy)
36-40 Rain Showers (no Intensity, very light, light, moderate, heavy)
41-45 Hail (no Intensity, very light, light, moderate, heavy)
46-50 Frost (no Intensity, very light, light, moderate, heavy)
51-55 Freezing Drizzle (no Intensity, very light, light, moderate, heavy)
56-60 Freezing Rain (no Intensity, very light, light, moderate, heavy)
61-65 Ice Pellets (no Intensity, very light, light, moderate, heavy)
66-70 Snow (no Intensity, very light, light, moderate, heavy)
71-75 Snow Showers (no Intensity, very light, light, moderate, heavy)
76-80 Thunderstorms (no Intensity, very light, light, moderate, heavy)
Hazards Table
0 No Hazards
1 Frequent Lightning
2 Gusty Winds
3 Heavy Rain
4 Damaging Wind
5 Small Hail
6 Large Hail
7 Outlying Areas
8 On Bridges and Overpasses
14
Example Weather in ArcView

• In /degrib/ArcView/, there is a weather.avl
  which was applied to the Wx-Inten 1 to create
  this image.
• Problem Chance of thunderstorms (T), and severe
  T have the same color.
• Intent get people started.
• If you have a better .avl, and want to share, let
  me know.

15
Weather .flt -SimpleWx
0 ltNoWxgt 20 R/IP (Rain / Ice Pellets) Low 40 R/ZR (Rain / Freezing Rain) High
1 L (Drizzle) Low Probability 21 S/IP (Snow / Ice Pellets) Low 41 ZR- (light Freezing Rain) High
2 R- (light Rain) Low 22 R/S (Rain / Snow) High Probability 42 ZR (Freezing Rain) High
3 R (Rain) Low 23 RW/SW (Rain / Snow Showers) High 43 ZR (heavy Freezing Rain) High
4 R (heavy Rain) Low 24 R/IP (Rain / Ice Pellets) High 44 R/ZR (Rain / Freezing Rain) High
5 R/T (Rain Thunder) Low 25 S/IP (Snow / Ice Pellets) High 45 ZR/IP (Freezing Rain / Ice Pellets) High
6 RW (Rain Showers) Low 26 IP- (light Ice) Low 46 SW (Snow Showers) Low Probability
7 RW/T (Rain Showers Thunder) Low 27 IP (Ice) Low 47 S- (light Snow) Low
8 T (Thunderstorms) Low 28 IP (heavy Ice) Low 48 S (Snow) Low
9 L (Drizzle) High Probability 29 ZL (Freezing Drizzle) Low 49 S (heavy Snow) Low
10 R- (light Rain) High 30 R/ZL (Rain / Freezing Drizzle) Low 50 SW (Snow Showers) High Probability
11 R (Rain) High 31 ZR- (light Freezing Rain) Low 51 S- (light Snow) High
12 R (heavy Rain) High 32 ZR (Freezing Rain) Low 52 S (Snow) High
13 R/T (Rain Thunder) High 33 ZR (heavy Freezing Rain) Low 53 S (heavy Snow) High
14 RW (Rain Showers) High 34 R/ZR (Rain / Freezing Rain) Low 54 Fog
15 RW/T (Rain Showers Thunder) High 35 ZR/IP (Freezing Rain / Ice Pellets) Low 55 Haze
16 T (Thunderstorms) High 36 IP- (light Ice) High 56 Smoke
17 Severe Thunder storms 37 IP (Ice) High 57 Blowing Snow
18 R/S (Rain / Snow) Low Probability 38 IP (heavy Ice) High 58 Blowing Dust
19 RW/SW (Rain / Snow Showers) Low 39 ZL (Freezing Drizzle) High
16
Example .flt -SimpleWx
17
NDFD CONUS Map Projection

• For CONUS (continental U.S.), NDFD uses a Lambert
  Conformal Conic Map Projection
• Tangent latitutude 25, orientation longitude -95,
  mesh latitude 25, mesh size 5079.406 m.
• In ESRI ArcMap that would be
• 1st Parallel 2nd Parallel 25 degrees north
  (tangent latitude)
• Lon of center of projection -95 degrees
  (orientation longitude)
• Lat of center of projection 25 degrees (tangent
  latitude)
• 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 km
• 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.
• To assist ESRI ArcView 3.x, degrib creates a .ave
  (ArcView Avenue script) to set the projection and
  radius correctly.

18
Un-projected vs Projected
19
When Earth Radii go Bad.
GOOD Point used 6371.2 km Polygon used 6371.2 km
BAD Point used 6371.2 km Polygon used 6367.47 km
20
Degrib Using superImageGen

• To generate images using superImageGen
• Select the Download tab
• Highlight the sector in question
• Download the data
• Click on Generate Images
• This results in the following
• Tkdegrib generates a set of .mosaic files
• superImageGen generates the corresponding .png
  images
• htmlmaker generates a set of web pages to browse
  the .png files
• IE is called to view the web pages.

21
CONUS MaxT using superImageGen
22
Degrib Probe point

• This is for people who know their lat/lon and
  just want text output. To probe a point from a
  command prompt (not available yet in tkdegrib)
  
• C\ndfd\degrib1.2\bin\degrib maxt.bin P pnt
  38.99,-77.03
• C\ndfd\degrib1.2\bin\degrib maxt.bin P pntFile
  point.txt
• 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 form allows
  for numerous stations.
• By default, probe chooses the nearest grid
  cell, but using the -Interp option, causes it
  to perform bi-linear interpolation.
• Everything previously discussed can be done using
  degrib, except data download, so the degrib step
  can be automated. See (./degrib1.2/docs/degrib.tx
  t for help)

23
Probe point (MaxT, MinT, PoP)
element, unit, refTime, validTime,
(38.993600,-77.022400) PoP12, , 200307212300,
200307220000, 39.000 PoP12, , 200307212300,
200307221200, 39.000 PoP12, , 200307212300,
200307230000, 50.000 PoP12, , 200307212300,
200307231200, 50.000 PoP12, , 200307212300,
200307240000, 50.000 PoP12, , 200307212300,
200307241200, 50.000 PoP12, , 200307212300,
200307250000, 20.000 PoP12, , 200307212300,
200307251200, 20.000 PoP12, , 200307212300,
200307260000, 14.000 PoP12, , 200307212300,
200307261200, 5.000 PoP12, , 200307212300,
200307270000, 5.000 PoP12, , 200307212300,
200307271200, 11.000 PoP12, , 200307212300,
200307280000, 11.000 PoP12, , 200307212300,
200307281200, 21.000 PoP12, , 200307212300,
200307290000, 21.000
element, unit, refTime, validTime,
(38.993600,-77.022400) MaxT, F, 200307212300,
200307230000, 86.882 MaxT, F, 200307212300,
200307240000, 82.375 MaxT, F, 200307212300,
200307250000, 85.233 MaxT, F, 200307212300,
200307260000, 87.753 MaxT, F, 200307212300,
200307270000, 89.395 MaxT, F, 200307212300,
200307280000, 87.775 MaxT, F, 200307212300,
200307290000, 86.800 element, unit, refTime,
validTime, (38.993600,-77.022400) MinT, F,
200307212300, 200307221200, 72.625 MinT, F,
200307212300, 200307231200, 73.165 MinT, F,
200307212300, 200307241200, 69.025 MinT, F,
200307212300, 200307251200, 65.965 MinT, F,
200307212300, 200307261200, 67.945 MinT, F,
200307212300, 200307271200, 69.745 MinT, F,
200307212300, 200307281200, 69.025
24
Degrib Future?

• Maintain the program by keeping up with NDFD as
  more variables / sectors are introduced.
• In order to inform users of updates, degrib has
  an announcement mailing list, which currently
  has 119 people on it.
• Improvements Based on user feedback, current
  thoughts are
• Create merged polygons. Instead of a polygon per
  cell, join similar values together to form large
  polygons.
• Create some form of graphical probe point
  capability
• Create some form of un-compressed database so
  that a CGI callable probe program can be used to
  access the data quickly
• Add some way for UNIX users (without GrADS) to
  plot the images
• Add some way for users to zoom in on a map
• Interface to more file formats