DeGRIB NDFD Weather

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:

  1. Coverage / Probability

  2. Weather Type

  3. Intensity

  4. Visibility

  5. 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

Hail was removed 8/12/2004

FR

Frost

ZL

Freezing Drizzle

ZR

Freezing Rain

IP

Ice Pellets (sleet)

S

Snow

SW

Snow Showers

T

Thunderstorms

 

 

Added 1/20/2004

BN

Blowing Sand

ZF

Freezing Fog

IC

Ice Crystals

IF

Ice Fog

VA

Volcanic Ash

ZY

Freezing Spray

WP

Water Spouts

 

 

 

The possibilities for Intensity are:

Code Meaning Code Meaning

<NoInten>

No Intensity

--

Very Light

-

Light

m

Moderate

+

Heavy

 

 

 

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

 

 

Added 8/13/2004

OGA

On Grassy Areas

Dry

dry

TOR

Tornado

Primary

Highest Ranking

Mention

Include Unconditionally

OR

or

MX

mixture

 

 


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:

  1. Output the weather string:
    degrib wx.bin -P -pnt 35,-76 -WxParse 0

  2. Convert the weather string to english:
    degrib wx.bin -P -pnt 35,-76 -WxParse 1

  3. Convert 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:

  1. Simple weather code 1: 6/2003 version

  2. Simple weather code 2 & 3: 1/2004 & 2/2004 version

  3. 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 wxshp.php.)

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

  1. 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)

  2. 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

  1. 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.

  2. 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.

  3. 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 degrib_wxshp)

  • Cover: A numeric value for coverage. (see degrib_wxshp)

  • Hazard: A numeric value for hazards. (see degrib_wxshp)

DeGRIB for NDFD