How NDFD Treats wwaHazards

wwaHazards(Watch, Warning, Advisory Hazards) in NDFD is handled by including a wwaHazard string table in the local use section of the GRIB2 message. The grid cell values in the data part of the GRIB2 message are numbers(Codes) which refer to that entry in the wwaHazard string table. The entries consist of ASCII wwaHazard strings which have up to 5 wwaHazards separated by '^'.  Simple wwaHazards are of the form "AA.B^CC.D" where AA and CC are a two letter descriptor unique to each Hazard, and B and D are either a "W" for Warning, an "A" for Watch, a "Y" for Advisory or a "S" for statement.

Simple Hazard code

In order to create graphical images of wwaHazards, NDFD needed a way to combine the various possibilities of wwaHazards into a discrete number of colors. So they came up with NDFD simple wwaHazards codes. degrib currently (as of 10/2024) recognizes five iterations of simple wwaHazards codes, as follows:

      1 = initial version of NDFD Simple Hazard(WWA) Code
      2 = 9/2008 version of NDFD Simple Hazard(WWA) Code
      3 = 7/2009 version of NDFD Simple Hazard(WWA) Code
      4 = 3/2017 version of NDFD Simple Hazard(WWA) Code
      5 = 10/2024 version of NDFD Simple Hazard(WWA) Code(default)

Note: If there are more than one wwaHazards at a certain grid point, degrib will always pick up on the lowest Code value of a wwaHazard. The lower the Code the higher the priority. For example, what if we have a wwaHazard of "HU.W^EC.A"? See the Simple Hazard(WWA) Code Table below. Hurricane Warning has a Code of "19", and Extreme Cold Watch has a Code of "94", so degrib will pick up on the HU.W and ignore the EC.A. 

Please see Handling wwaHazard in Degrib(below), or our man page, for instructions on how to work with wwaHazards in degrib. 

Current(version 5) Simple Hazard(WWA) Code Table:

Handling wwaHazards in Degrib

Handing wwaHazards: Degrib -P Option

Degrib has several different ways of handling wwaHazards. Starting with the "degrib -P" option, it can:

1. Output the wwaHazards string:
   degrib ds.wwa.bin -P -pnt 35,-76 -WxParse 0
2. Convert the wwaHazards string to english:
   degrib ds.wwa.bin -P -pnt 35,-76 -WxParse 1
3. Convert the wwaHazards string to an NDFD simple wwaHazards code:
   degrib ds.wwa.bin -P -pnt 35,-76 -WxParse 2

Handling wwaHazards: Degrib -C Option

Continuing to the "degrib -C" option, it is limited in some respects by the file formats that it writes to.

The -C -Flt option

1. degrib ds.wwa.bin -C -Flt -Met -msg 1 => convert the message to a NxM 4 byte float file where each cell contains the number in the wwaHazards string lookup table contained in the .txt file (created with the default -Met option)
2. degrib ds.wwa.bin -C -Flt -nMet -msg 1 -SimpleWWA 5=> convert the message to a NxM 4 byte float file using simple wwaHazards scheme 5 (see Table above).

The -C -Csv option

1. degrib ds.wwa.bin -C -Csv -msg 1 => convert the message to an ASCII comma delimited file with a x, y, lat, lon, and wwaHazards value for each cell. In this case the wwaHazards value is the wwaHazards string.
2. degrib ds.wwa.bin -C -Csv -msg 1 -WxParse 1 => convert the message to an ASCII comma delimited file with a x, y, lat, lon, and wwaHazards value for each cell. In this case the wwaHazards value is the wwaHazards string converted to english.
3. degrib ds.wwa.bin -C -Csv -msg 1 -WxParse 2 => convert the message to an ASCII comma delimited file with a x, y, lat, lon, and wwaHazards value for each cell. In this case the wwaHazards value is the wwaHazards string converted to an NDFD simple wwaHazards code (see Table above).