DeGRIB NDFD Weather - MDL
How NDFD Treats Weather
Weather in NDFD is handled by including a weather 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 which refer to that entry in the weather string table. The entries consist of ASCII weather strings which have upto 5 weather words separated by '^'.
Each weather word has 5 pieces separated by ':'. The 5 pieces of the weather word are as follows:
Coverage / Probability
Weather Type
Intensity
Visibility
Hazards (Attributes)
The possibilities for Coverage / Probability are:
Code | Meaning | Code | Meaning |
---|---|---|---|
<NoCov> | No Coverage / probability | Iso | Isolated |
Sct | Scattered | Num | Numerous |
Wide | Widespread | Ocnl | Occasional |
SChc | Slight Chance | Chc | Chance of |
Lkly | Likely | Def | Definite |
Patchy | Patchy | Areas | Areas of |
Added 8/13/2004 | |||
Pds | Periods of | Frq | Frequent |
Inter | Intermittent | Brf | Brief |
The possibilities for Weather Type are:
Code | Meaning | Code | Meaning |
---|---|---|---|
<NoWx> | No Weather | K | Smoke |
BD | Blowing Dust | BS | Blowing Snow |
H | Haze | F | Fog |
L | Drizzle | R | Rain |
RW | Rain Showers | A | Hail |
FR | Frost | ZL | Freezing Drizzle |
ZR | Freezing Rain | IP | Ice Pellets (sleet) |
S | Snow | SW | Snow Showers |
T | Thunderstorms |
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BN | Blowing Sand | ZF | Freezing Fog |
IC | Ice Crystals | IF | Ice Fog |
VA | Volcanic Ash | ZY | Freezing Spray |
WP | Water Spouts |
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The possibilities for Intensity are:
Code | Meaning | Code | Meaning |
---|---|---|---|
<NoInten> | No Intensity | -- | Very Light |
- | Light | m | Moderate |
+ | Heavy |
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The possibilities for Visibility are:
<NoVis>, 0SM, 1/4SM, 1/2SM, 3/4SM, 1SM, 11/2SM, 2SM, 21/2SM, 3SM, 4SM, 5SM, 6SM, P6SM
The posibilities for Hazards (Attributes) are:
(Hazards (or Attributes) are broken up into up to 5 pieces separated by ','s. )
Code | Meaning | Code | Meaning |
---|---|---|---|
None | None | FL | Frequent Lightning |
GW | Gusty Winds | HvyRn | Heavy Rain |
DmgW | Damaging Wind | SmA | Small Hail |
LgA | Large Hail | OLA | Outlying Areas |
OBO | on Bridges and Overpasses |
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Added 8/13/2004 | |||
OGA | On Grassy Areas | Dry | dry |
TOR | Tornado | Primary | Highest Ranking |
Mention | Include Unconditionally | OR | or |
MX | mixture |
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Handling Weather in Degrib
Handing Weather: Degrib -P Option
Degrib has several different ways of handling weather. Starting with the "degrib -P" option, it can:
Output the weather string:
degrib wx.bin -P -pnt 35,-76 -WxParse 0Convert the weather string to english:
degrib wx.bin -P -pnt 35,-76 -WxParse 1Convert the weather string to an NDFD simple weather code:
degrib wx.bin -P -pnt 35,-76 -WxParse 2
What is an NDFD simple weather code?
In order to create graphical images of weather, NDFD needed a way to combine the various possibilities of weather into a discrete number of colors. So they came up with NDFD simple weather codes
degrib currently (as of 12/15/2006) recognizes four iterations of simple weather codes, as follows:
Simple weather code 1: 6/2003 version
Simple weather code 2 & 3: 1/2004 & 2/2004 version
Simple weather code 4: 11/2004 version
(Note: If you are interested in encoding schemes, you might also be interested in how we encoded the weather for ESRI Shapefiles. You may also view https://vlab.noaa.gov/web/mdl/degrib-ndfd-weather-shape-file-fields.)
To get a particular simple weather code using the -P option use:
degrib wx.bin -P -pnt 35,-76 -WxParse 2 -SimpleVer 2
Note: -SimpleVer defaults to the most recent one (currently 4).
Handling Weather: 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
degrib wx.bin -C -Flt -Met -msg 1 => convert the message to a NxM 4 byte float file where each cell contains the number in the weather string lookup table contained in the .txt file (created with the default -Met option)
degrib wx.bin -C -Flt -nMet -msg 1 -SimpleVer 2 -SimpleWx => convert the message to a NxM 4 byte float file using simple weather scheme 2 (see above).
The -C -Csv option
degrib wx.bin -C -Csv -msg 1 => convert the message to an ASCII comma delimited file with a x, y, lat, lon, and weather value for each cell. In this case the weather value is the weather string.
degrib wx.bin -C -Csv -msg 1 -WxParse 1 => convert the message to an ASCII comma delimited file with a x, y, lat, lon, and weather value for each cell. In this case the weather value is the weather string converted to english.
degrib wx.bin -C -Csv -msg 1 -WxParse 2 => convert the message to an ASCII comma delimited file with a x, y, lat, lon, and weather value for each cell. In this case the weather value is the weather string converted to an NDFD simple weather code (see above).
The -C -Shp (and -C -Shp2) options
With shapefiles, I could get creative, so I broke up the weather into more of its component parts. The data I provide are as follows:
Wx: The original weather string.
Wx-index: The index into the original weather table that came with the message.
Visibility: The minimum visibility in the 5 weather words, in 1/32 of a statute mile.
Ndfdwxcode: The NDFD simple weather code (see above)
Next, for each of the 5 weather words, I provide the following:
Weather: An english translation of the weather word.
Wx-inten: A combination of the weather type and the intensity. (see https://vlab.noaa.gov/web/mdl/degrib-ndfd-weather-shape-file-fields)
Cover: A numeric value for coverage. (see https://vlab.noaa.gov/web/mdl/degrib-ndfd-weather-shape-file-fields)
Hazard: A numeric value for hazards. (see https://vlab.noaa.gov/web/mdl/degrib-ndfd-weather-shape-file-fields)