![](media/image1.jpeg){width="0.9159722222222222in"
height="0.9166666666666666in"}

**Representing the National Center for Environmental Prediction /
Aviation Weather Center (NCEP/AWC) Graphical Area Forecast (GFA) Data in
BUFR**

**Version 1.0**

**November 2005**

Table of Contents

Document Identification Sheet

+-----------------------------+--------------+-------------------------+
| **DOCUMENT DESCRIPTION**    |              |                         |
+-----------------------------+--------------+-------------------------+
| **Document title:           |              |                         |
| Representing AWC Graphical  |              |                         |
| Area Forecast (GFA) Data in |              |                         |
| BUFR.**                     |              |                         |
+-----------------------------+--------------+-------------------------+
| **Document Reference        | **Issue :    |                         |
| Number**                    | DRAFT 1.0**  |                         |
+-----------------------------+--------------+-------------------------+
|                             | **Date Of    |                         |
|                             | Issue :      |                         |
|                             | 9/2005**     |                         |
+-----------------------------+--------------+-------------------------+
| **Abstract**                |              |                         |
|                             |              |                         |
| This document provides      |              |                         |
| guidelines for the correct  |              |                         |
| depiction of AWC GFA data   |              |                         |
| from BUFR code.             |              |                         |
+-----------------------------+--------------+-------------------------+
| **Keywords: GFA BUFR**      |              |                         |
+-----------------------------+--------------+-------------------------+
| **Disk Reference/ File      |              |                         |
| Name**                      |              |                         |
+-----------------------------+--------------+-------------------------+
| **Contact : C. Wallace**    | **Tel:**     | **E-mail:**             |
|                             |              |                         |
| **Aviation Weather Center** | **(816)      | **Cli                   |
|                             | 584-7248**   | nton.Wallace@noaa.gov** |
| **Kansas City, Missouri**   |              |                         |
+-----------------------------+--------------+-------------------------+

Document Change Record

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  **Issue**   **Date**      **Reason for Change**            **Section Pages
                                                             Affected**

                                                             
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1.  **The BUFR Format**

    1.  **Introduction**

> BUFR stands for Binary Universal Form for the Representation of
> meteorological data. It is a standard developed by the World
> Meteorological Organization (WMO; see WMO Manual 306 Part B for
> technical specification, which can be procured via the WMO web site -
> http://www.wmo.ch/index-en.html) for the efficient storage of
> meteorological features in a machine independent form, where all the
> information to describe the features are contained within the data.
>
> This document has been prepared by the Aviation Weather Center (AWC)
> for the purpose of providing guidance to software developers who have
> the task of constructing Graphical Area Forecast (GFA) BUFR
> visualization software**.** The document is designed to assist
> developers in the construction of compliant visualization software
> that receives its data input from text files obtained from BUFR
> decoding software supplied by the AWC
>
> The AWC has produced this document with the intention of circulating
> it to all interested parties. If additional guidance or advice in
> regard to any of the items included in this document is required, then
> users, software manufacturers and State Authorities are invited to
> contact the AWC. A consultancy service is available to assist these
> users. Please contact Clinton Wallace for further information: -
> E-mail: <Clinton.Wallace@noaa.gov> Tel: (816) 584-7248.

2.  **Scope of Document**

3.  **Concepts**

> To produce a BUFR file two elements are needed: 1) A file of raw data
> and 2) a set of tables containing descriptors. When the raw data is
> encoded each data value is attached to a descriptor which defines what
> that data represents. The decoding process reads the BUFR file, looks
> up the descriptor in the relevant table and writes out the information
> in whatever format is needed.

1.  ***BUFR Tables***

> The binary BUFR files contain a set of tables' descriptors and data
> values. To be able to understand what the values represent the
> descriptors need to be decoded from a set of common tables that sit on
> the local machine. This format means that the BUFR messages are very
> small and are machine independent. They can be understood and decoded
> by any BUFR decoder which has the latest tables available.

2.  ***Representation***

> Data held in the BUFR format is completely independent of the way in
> which the data is depicted on GFA charts. Only the information that
> describes the feature is encoded. For example, an area of aircraft
> icing is a list of points with the height of the base and top. There
> is nothing in the BUFR bulletin about how the icing area should be
> drawn, or how the attributes are to be displayed. This depiction is
> arbitrary, and is determined by the graphical display program. This
> document has been produced to assist in this regard. It is recommended
> that the overall aim of BUFR visualization, as stated in section 1.1,
> should be carefully considered.

3.  ***Standards***

> Although no information is given in BUFR on how to visually represent
> the data, rules have been laid down by the International Civil
> Aviation Organization (ICAO) and WMO. The ICAO requirements are laid
> out in *Annex 3, Meteorological Service for International Air
> Navigation* in the *International Standards and Recommended Practices*
> document. WMO Manual 306 Part B should be the standard used for the
> BUFR code itself.

4.  ***Open and Closed Areas***

> The boundaries of areas of some of the GFA elements are described as
> being either "open" or "closed". Closed areas are defined as regions
> that have identical first and last coordinates. Open areas have
> different start and end coordinates. Both open and closed areas are
> used in the GFA.

5.  ***Unit Conversions***

6.  ***WMO Message Header Ids***

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2.  **Header Representation**

> A BUFR message will always be packaged between the characters 'BUFR'
> and '7777'. Before the data representing the features appears, a
> header is always found that details where the message has come from,
> the date and valid times, regional information, and ICAO information.

1.  **Message Header for Graphical AIRMET (Tango, Sierra, and Zulu)**

2.  **Message Header for Graphical Area Forecast**

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3.  **Features Represented**

    1.  **Graphical AIRMET Sierra**

> Graphical AIRMET Sierra consists of the following phenomena:

-   IFR Ceiling

-   IFR Visibility

-   Mountain Obscuration

    1.  **Graphical AIRMET Tango**

> Graphical AIRMET Tango consists of the following phenomena:

-   Moderate Turbulence

-   Sustained Strong Surface Winds (\> 30 knots)

-   Low Level Wind Shear

    1.  **Graphical AIRMET Zulu**

> Graphical AIRMET Zulu consists of the following phenomena:

-   Moderate Icing

-   Freezing Levels

-   Multiple Freezing Levels

    1.  **Other Graphical Area Forecast Elements**

> The GFA consists of all of the above phenomena in addition to:

-   Thunderstorms

-   Mountain Wave Turbulence

-   Pressure Centers and Fronts

-   Tropical Storms

-   Precipitation

-   Volcanic Eruption

-   MVFR Visibility

-   Towering Cumulus Clouds

-   Clouds

4.  **Graphical AIRMET Sierra**

    1.  **IFR Ceiling Representation**

> IFR CIG is represented on a G-AIRMET Sierra chart as an area drawn
> with a line. IFR CIG will depict areas of cloud ceilings with bases
> less than 1000 feet above ground level (AGL). The appropriate text
> label is located at the center of the hazard area polygon. There is no
> symbol associated with areas of IFR CIG.

1.  ***BUFR Sequence***

> Table 1 shows the BUFR sequence for *IFR CIG*. In BUFR, how the data
> is depicted is not specified. Only the points describing the area and
> the attributes associated with that area are held.

  --------- -------- -----------------------------------------------------
                     **GFA IFR CIG and Visibility**

  3 16 054  1 12 000 Replicate 12 descriptors (Number of replications =
                     Number of areas of IFR CIG)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            0 20 006 Flight rules, 1=IFR

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 027 Description of feature

            0 20 008 Cloud distribution for aviation, 3=Broken, 4=Overcast

            0 20 014 Height of top of cloud

            0 20 001 Horizontal visibility (m)

            0 03 042 Description of feature, 1=ABV/AOA, 3=BLW/AOB,\
                     7=Missing

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 1: G-AIRMET Sierra IFR CIG BUFR Sequence**

2.  ***Feature Header***

> **IFR CIG Type of feature**
>
> **1 Number of areas of IFR CIG in the list**

3.  ***Feature Data***

> *1st row = heights of CIG base and top in meters, 2nd row =*
>
> *number of points in area. These are followed by two columns
> containing latitude and longitude data. The numbers in the last row
> indicate the flight rules (1=IFR) and the cloud distribution for
> aviation (3=BROKEN, 4=OVERCAST)).*

2.  **IFR Visibility Representation**

> IFR visibility is represented on a G-AIRMET Sierra chart as an area
> drawn with a line. IFR visibility will depict areas where the
> prevailing visibility is less than 3 statute miles. The appropriate
> text label is located at the center of the hazard area polygon. There
> is no symbol associated with areas of IFR visibility
>
> .

1.  ***BUFR Sequence***

> BUFR sequence for *IFR VIS* is shown in Table 1. In BUFR, how the data
> is depicted is not specified. Only the points describing the area and
> the attributes associated with that area are held.

2.  ***Feature Header***

> **IFR VIS Type of feature**
>
> **1 Number of areas of IFR VIS in the list**

3.  ***Feature Data***

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3.  **Mountain Obscuration Representation**

> Mountain obscuration is represented on a G-AIRMET Sierra chart as a
> single line. The appropriate label for mountain obscuration (Figure 1)
> is located at the center of the hazard area polygon.
>
> ![](media/image2.png)
>
> **Figure 1: Mountain obscuration label**

1.  ***BUFR Sequence***

> Table 3 shows the BUFR sequence for *mountain obscuration*. In BUFR,
> how the data is depicted is not specified. Only the points describing
> the line and the attributes associated with that line are held.

  --------- -------- -----------------------------------------------------
                     **GFA Mountain Obscuration**

  3 16 055  1 08 000 Replicate 8 descriptors (Number of replications =
                     Number of areas of mountain obscuration)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            0 20 025 Obscuration, 14=Mountain

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 027 Description of feature

            0 08 011 Meteorological feature, 12=Cloud, 63=Missing

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 2: G-AIRMET Sierra Mountain Obscuration BUFR Sequence**

2.  ***Feature Header***

> **MT OBSC Type of feature**
>
> **1 Number of lines of mountain obscuration in the list**

3.  ***Feature Data***

> *1st row = number of points on the line. These are followed by two
> columns containing latitude and longitude data. A single number in the
> last row indicates the type of obscuration (14=MOUNTAIN).*

5.  **Graphical AIRMET Tango**

    1.  **Moderate Turbulence Representation**

> Moderate turbulence is represented on a G-AIRMET Tango chart as an
> area drawn with a line. The appropriate intensity label is located at
> the center of the hazard area polygon. The base and top of the
> turbulence layer (100's feet AMSL or FL) will be included in the drawn
> area
>
> Please note that open and closed boundaries are used for encoding
> turbulence information -- see section 1.3.4.

1.  ***BUFR Sequence***

> Table 4 shows the BUFR sequence for *turbulence*. In BUFR, how the
> data is depicted is not specified. Only the points describing the area
> and the attributes associated with that area are held.

  --------- -------- ----------------------------------------------------
                     **GFA Turbulence**

  3 16 056  1 09 000 Replicate 9 descriptors (Number of replications =
                     Number of areas of CAT and/or mountain wave
                     turbulence)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 3=Volume

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 027 Description of feature

            0 08 011 Meteorological feature, 13=Turbulence, 23=Mountain
                     wave

            0 11 031 Degree of turbulence, 6=Moderate, 7=Severe

            0 08 011 Meteorological feature, Missing=Cancel

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- ----------------------------------------------------

> **Table 3: G-AIRMET Tango Moderate Turbulence BUFR Sequence**

2.  ***Feature Header***

> Contains the type of data to follow and the number of features in the
> list.
>
> **TURB Type of feature**
>
> **2 Number of turbulence areas in the list**

3.  ***From Line and Example***

> 60E BIS TO 60SE DLH TO 50WNW PXV TO 50E HLC TO 50SW RAP TO 60E BIS
>
> 20SW END TO 50SSW ARG TO 50SW VUZ TO 30ENE BTR TO 50SSE AUS TO 50WSW
> ABI TO 20SW END

![](media/image3.png){width="3.6145833333333335in"
height="3.2194444444444446in"}

4.  ***Feature Data***

> *1st row = heights of moderate turbulence base and top in meters, 2nd
> row = number of points in area. These are followed by two columns
> containing latitude and longitude data. The numbers in the last row
> indicate the meteorological feature (13=TURBULENCE) and the degree of
> turbulence (6=MODERATE).*

2.  **Sustained Strong Surface Winds Representation**

> Areas where the sustained surface winds are in excess of 30 knots
> specified at 10 meters above the ground are represented on a G-AIRMET
> Tango chart as an area drawn with a line. The appropriate speed in
> knots will be delineated on a label located in the center of the
> hazard area polygon.
>
> Please note that open and closed boundaries are used for encoding
> turbulence information -- see section 1.3.4.

1.  ***BUFR Sequence***

> Table 5 shows the BUFR sequence for *sustained strong surface winds*.
> In BUFR, how the data is depicted is not specified. Only the points
> describing the area and the attributes associated with that area are
> held.

  --------- -------- -----------------------------------------------------
                     **GFA Strong Surface Winds**

  3 16 057  1 09 000 Replicate 9 descriptors (Number of replications =
                     Number of areas of surface wind speed)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            1 01 000 Replicate 1descriptor

            0 31 001 Replication count

            3 01 023 Latitude, longitude

            0 11 012 Wind speed at 10 m

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 4: G-AIRMET Tango Sustained Strong Surface**
>
> **Winds BUFR Sequence**

2.  ***Feature Header***

> Contains the type of data to follow and the number of features in the
> list.
>
> **SFCWIND Type of feature**
>
> **1 Number of areas of sustained strong surface winds in the list**

3.  ***From Line and Example***

> 30N YOW TO 30E MPV TO 30ESE ALB TO 30NNE HTO TO 30WNW HAR TO 40S JHW
> TO 20WNW BUF TO 50SSW YOW TO 30N YOW
>
> ![](media/image4.png){width="3.8645833333333335in"
> height="3.441666666666667in"}

4.  ***Feature Data***

> *1st row = number of points in area. These are followed by two columns
> containing latitude and longitude data. A single number in the last
> row indicates the wind speed in knots at 10 meters.*

3.  **Low Level Wind Shear Representation**

> Areas of wind shear, other than that which is convectively induced,
> that exceed 10 knots per 100 feet below 2000 feet AGL are represented
> on a G-AIRMET Tango chart as an area. A text box with 'LLWS' inside it
> is associated with the area.

1.  ***BUFR Sequence***

> Table 6 shows the BUFR sequence for *low level wind shear*. In BUFR,
> how the data is depicted is not specified. Only the points describing
> the line and the attributes associated with that line are held.

  --------- -------- -----------------------------------------------------
                     **GFA Low Level Wind Shear**

  3 16 058  1 08 000 Replicate 8 descriptors (Number of replications =
                     Number of areas of low level wind shear)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            1 01 000 Replicate 1descriptor

            0 31 001 Replication count

            3 01 023 Latitude, longitude

            0 07 007 Height (m)

            0 11 063 Wind shear

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 5: G-AIRMET Tango Low Level Wind Shear BUFR Sequence**

2.  ***Feature Header***

> **LLWS Type of feature**
>
> **1 Number of areas of low level wind shear**

3.  ***From Line and Example***

30WSW MOT TO 20SW BJI TO 30NNW FOD TO 30SE ANW TO 60NNW

RAP TO 30WSW MOT

> ![](media/image5.png){width="3.6145833333333335in"
> height="3.2194444444444446in"}

4.  ***Feature Data***

> *1st row = number of points on the line. These are followed by two
> columns containing latitude and longitude data. The numbers in the
> last row indicate height in meters and the wind shear.*

6.  **Graphical AIRMET Zulu**

    1.  **Moderate Icing Representation**

> Moderate icing is represented on a G-AIRMET Zulu chart as an area
> drawn with a line. The appropriate intensity label is located at the
> center of the hazard area polygon. The base and top of the icing layer
> (100's feet AMSL or FL) will be included in the drawn area.
>
> Please note that open and closed boundaries are used for encoding
> icing information -- see section 1.3.4.

1.  ***BUFR Sequence***

> Table 7 shows the BUFR sequence for *moderate icing*. In BUFR, how the
> data is depicted is not specified. Only the points describing the line
> and the attributes associated with that line are held.

  --------- -------- ----------------------------------------------------
                     **GFA Icing**

  3 16 059  1 09 000 Replicate 9 descriptors (Number of replications =
                     Number of areas of icing)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            0 08 011 Meteorological feature, 15=Airframe Icing

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 027 Description of feature

            0 20 041 Airframe icing, 4=Moderate Icing, 7=Severe Icing

            2 04 000 Add associated field, Cancel

            0 08 011 Meteorological feature, Missing=Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- ----------------------------------------------------

> **Table 6: G-AIRMET Zulu Moderate Icing BUFR Sequence**

2.  ***Feature Header***

> Contains the type of data to follow and the number of features in the
> list.
>
> **ICING Type of feature**
>
> **1 Number of icing areas in the list**

3.  ***From Line and Example***

> 40WNW GSO TO 40NW ILM TO 40W CRG TO 30S ABY TO 20NNW ATL TO
>
> 40WNW GSO

![](media/image6.png){width="3.8645833333333335in"
height="3.441666666666667in"}

4.  ***Feature Data***

> *1st row = heights of aircraft icing base and top in meters, 2nd row =
> number of points in area. These are followed by two columns containing
> latitude and longitude data. A single number in the last row indicates
> the degree of aircraft icing (4=MODERATE).*

2.  **Freezing Level Representation**

> The freezing level heights are delineated by a single line on the GFA
> chart at 4000 feet AMSL intervals. A text box which details the height
> of the lowest freezing level (in hundreds of feet AMSL or SFC) is
> associated with each freezing level.

1.  ***BUFR Sequence***

> Table 8 shows the BUFR sequence for *freezing level heights*. In BUFR,
> how the data is depicted is not specified. Only the points describing
> the line and the attributes associated with that line are held.

  --------- -------- -----------------------------------------------------
                     **GFA Freezing Level(s)**

  3 16 060  0 08 040 Flight level significance, 13=Zero degrees Celsius
                     crossing

            1 06 000 Replicate 6 descriptors (Number of replications =
                     Number of areas of freezing levels)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 1=Line

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 027 Description of feature

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel

            0 08 040 Flight level significance, Missing = Cancel
  --------- -------- -----------------------------------------------------

> **Table 7: GFA Freezing Level(s) BUFR Sequence**

2.  ***Feature Header***

> **FZLVL Type of feature**
>
> **1 Number of freezing levels**

3.  ***Feature Data***

> *1st row = number of points on the line. These are followed by two
> columns containing latitude and longitude data. A single number in the
> last row indicates the flight level significance (13=ZERO DEGREES
> CELSIUS CROSSING).*

3.  **Multiple Freezing Levels Representation**

> Multiple freezing level heights are delineated by single lines on the
> GFA chart at 4000 feet AMSL intervals. A text box which details the
> height of the lowest freezing level (in hundreds of feet AMSL or SFC)
> is associated with each freezing level.

1.  ***BUFR Sequence***

> The BUFR sequence described in section 6*.2.1* can be used for
> multiple freezing levels.

2.  ***Feature Header***

> **FZLVL Type of feature**
>
> **3 Number of freezing levels**

3.  ***Feature Data***

> *1st row = number of points on the line. These are followed by two
> columns containing latitude and longitude data. A single number in the
> last row indicates the flight level significance (13=ZERO DEGREES
> CELSIUS CROSSING).*

7.  **Other Graphical Area Forecast Elements**

    1.  **Thunderstorm Representation**

> Thunderstorms are represented on a GFA chart as an area or volume
> drawn with a line, that is not included in an active SIGMET. The
> appropriate label is located at the center of the hazard polygon. The
> label will include the following information:

-   Optional modifiers

    -   OBSC (occasional)

    -   EMBD (embedded)

-   Frequency or coverage

    -   ISOL (isolated)

    -   OCNL (occasional)

    -   FRQ (frequent)

-   Optional hail indicator

-   Height of max cloud top

-   Height of cloud base

    1.  ***BUFR Sequence***

> Table 9 shows the BUFR sequence for *thunderstorms*. In BUFR, how the
> data is depicted is not specified. Only the points describing the line
> and the attributes associated with that line are held.

  --------- ----------- --------------------------------------------------
                        **GFA Thunderstorms**

  3 16 061  3 16 050    GFA Header

            0 08 011    Meteorological feature, 21=Thunderstorm

            1 10 000    Replicate 10 descriptors (Number of replications =
                        Number of areas of forecast thunderstorms)

            0 31 001    Replication count

            0 08 007    Dimensional significance, 2=Area

            0 20 021    Type of precipitation, 14=Hail

            2 04 001    Add associated field

            0 31 021    Associated field significance, 21: 0=original
                        value, 1=substituted/corrected value

            3 01 027    Latitude, longitude, flight level (base and top)

            0 20 008    Cloud distribution for aviation, 8=Isolated,
                        10=Occasional, 12=Frequent, 15=Obscured,
                        16=Embedded

            0 20 013    Height of base of cloud

            0 20 014    Height of top of cloud

            2 04 000    Add associated field, Cancel

            0 08 007    Dimensional significance Missing=Cancel

            0 08 011    Meteorological feature, Missing=Cancel
  --------- ----------- --------------------------------------------------

> **Table 8: GFA Thunderstorms BUFR Sequence**

2.  ***Feature Header***

> **TSTM Type of feature**
>
> **2 Number of thunderstorms**

3.  ***Feature Data***

> *1st row = heights of thunderstorms base and top in meters, 2nd row =
> number of points in area. These are followed by two columns containing
> latitude and longitude data. The numbers in the last row indicate the
> meteorological feature (21=THUNDERSTORM), the type of precipitation
> (14=HAIL), and the cloud distribution for aviation (8=ISOLATED,
> 10=OCCASIONAL, 12=FREQUENT, 15=OBSCURED, or 16=EMBEDDED).*

1.  **Mountain Wave Representation**

> Mountain waves are represented on a GFA chart as an area drawn with a
> line. The appropriate intensity label is located at the center of the
> hazard area polygon. The base and top of the turbulence layer (100's
> feet AMSL or FL) will be included in the drawn area.
>
> Please note that open and closed boundaries are used for encoding
> turbulence information -- see section 1.3.4.

1.  ***BUFR Sequence***

> The BUFR sequence described in section *4.1.1* can be used for
> mountain waves.

2.  ***Feature Header***

> Contains the type of data to follow and the number of features in the
> list.
>
> **MTW Type of feature**
>
> **2 Number of mountain wave areas in the list**

3.  ***Feature Data***

> *1st row = heights of mountain wave base and top in meters, 2nd row =
> number of points in area. These are followed by two columns containing
> latitude and longitude data. The numbers in the last row indicate the
> meteorological feature (23=MOUNTAIN WAVE) and the degree of turbulence
> (6=MODERATE, 7=SEVERE).*

2.  **Pressure Centers and Fronts Representation**

    1.  ***BUFR Sequence***

> Table 10 shows the BUFR sequence for *pressure centers and fronts*. In
> BUFR, how the data is depicted is not specified. Only the points
> describing the line and the attributes associated with that line are
> held.

  --------- -------- -----------------------------------------------------
                     **GFA Pressure Centers and Fronts**

  3 16 062  3 16 050 GFA Header

            1 09 000 Replicate 9 descriptors Number of replications =
                     Number of tropical storms)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 0=Point

            0 19 001 Type of synoptic feature, 2=Tropical Storm

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 023 Latitude, longitude

            0 19 005 Direction of motion

            0 19 006 Speed of motion of feature

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel

            1 09 000 Replicate 9 descriptors (Number of replications =
                     Number of pressure centers)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 0=Point

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 023 Latitude, longitude

            0 07 004 Pressure (Pa)

            0 19 005 Direction of motion

            0 19 006 Speed of motion of feature

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel

            1 12 000 Replicate 12 descriptors (Number of replications =
                     Number of fronts)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 1=Line

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            0 08 011 Front, 0=Quasi Stationary front at the surface,
                     2=Warm front at the surface, 4=Cold front at the
                     surface, 6=Occlusion, 26=Trough

            1 01 000 Replicate one descriptor

            0 31 001 Replication count

            3 01 023 Latitude, longitude

            0 19 005 Direction of motion

            0 19 006 Speed of motion of feature

            0 08 011 Front, Missing=Cancel

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 9: GFA Pressure Centers and Fronts BUFR Sequence**

2.  ***Feature Header***

3.  ***Feature Data***

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3.  **Tropical Storms Representation**

    1.  ***BUFR Sequence***

> The BUFR sequence described in section 7*.3.1* can be used for
> tropical storms.

2.  ***Feature Header***

3.  ***Feature Data***

```{=html}
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```
4.  **Precipitation Representation**

    1.  ***BUFR Sequence***

> Table 11 shows the BUFR sequence for *precipitation*. In BUFR, how the
> data is depicted is not specified. Only the points describing the line
> and the attributes associated with that line are held.

  --------- -------- -----------------------------------------------------
                     **GFA Precipitation**

  3 16 062  3 16 050 GFA header

            1 10 000 Replicate 10 descriptors (Number of replications =
                     Number of areas of precipitation)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 023 Latitude, longitude

            0 20 021 Type of Precipitation, 2=Liquid precipitation not
                     freezing, 3=Liquid freezing precipitation, 6=Solid
                     precipitation, 7=Snow

            0 20 022 Character of precipitation, 1=Continuous,
                     2=Intermittent

            0 20 025 Obscuration, 8=Haze, 11=Dust, 12=Sand,

            0 20 024 Intensity of phenomena, 1=Light, 2=Moderate, 3=Heavy,
                     4=Violent

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 10: GFA Precipitation BUFR Sequence**

2.  ***Feature Header***

3.  ***Feature Data***

```{=html}
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```
5.  **Volcanic Eruption(s) Representation**

> The location of active volcanic eruption(s), including the name of the
> volcano and its coordinates are represented with a symbol (Figure 3)
> on the GFA chart.
>
> ![](media/image7.png)
>
> **Figure 3: Volcanic eruption symbol**

1.  ***BUFR Sequence***

> Table 12 shows the BUFR sequence for *volcanic eruptions*. In BUFR,
> how the data is depicted is not specified. Only the points describing
> the line and the attributes associated with that line are held.

  --------- -------- ----------------------------------------------------
                     **GFA Volcanic Eruption(s)**

  3 16 063  3 16 050 GFA header

            0 08 011 Meteorological feature, 17=Volcano

            1 07 000 Replicate 7 descriptors (Number of replications =
                     Number of areas of volcanic ash activity)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 0=Point

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 023 Latitude, longitude

            0 01 022 Name of feature

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel

            0 08 011 Meteorological feature, Missing=Cancel
  --------- -------- ----------------------------------------------------

> **Table 11: GFA Volcanic Eruption(s) BUFR Sequence**

2.  ***Feature Header***

> **VA Type of feature**
>
> **2 Number of volcanic eruptions**

3.  ***Feature Data***

> *1st row = two columns containing latitude and longitude data. The
> numbers in the last row indicate the meteorological feature
> (17=VOLCANO) and the name of the volcano.*

6.  **MVFR Visibility Representation**

    1.  ***BUFR Sequence***

> Table 13 shows the BUFR sequence for *MVFR visibility*. In BUFR, how
> the data is depicted is not specified. Only the points describing the
> line and the attributes associated with that line are held.

  --------- -------- -----------------------------------------------------
                     **GFA MVFR Visibility**

  3 16 064  3 16 050 GFA Header

            1 11 000 Replicate 11 descriptors (Number of replications =
                     Number of areas of MVFR)

            0 31 001 Replication count

            0 08 007 Dimensional significance, 2=Area

            0 20 006 Flight rules, 2=MVFR

            0 20 025 Obscuration, 1=Fog

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            1 01 000 Replicate 1 descriptor

            0 31 001 Replication count

            3 01 023 Latitude, longitude

            0 20 003 Present weather

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 12: GFA MVFR Visibility BUFR Sequence**

2.  ***Feature Header***

3.  ***Feature Data***

```{=html}
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```
7.  **Towering Cumulus Cloud Representation**

    1.  ***BUFR Sequence***

> Table 14 shows the BUFR sequence for *towering cumulus clouds*. In
> BUFR, how the data is depicted is not specified. Only the points
> describing the line and the attributes associated with that line are
> held.

  --------- -------- -----------------------------------------------------
                     **GFA Towering Cumulus Clouds**

  3 16 065  3 16 050 GFA header

            1 11 000 Replicate 11 descriptors (Number of replications =
                     Number of areas of TCU)

            0 31 001 Replication count

            3 01 023 Latitude, longitude

            0 08 007 Dimensional significance, 3=Volume

            0 20 012 Cloud type, 32=Towering Cumulus

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            3 01 027 Description of feature

            0 20 008 Cloud distribution for aviation, 10=occasional,
                     12=Frequent

            0 20 013 Height of base of cloud

            0 20 014 Height of top of cloud

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 13: GFA Towering Cumulus Clouds BUFR Sequence**

2.  ***Feature Header***

3.  ***Feature Data***

```{=html}
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```
8.  **Cloud Representation**

    1.  ***BUFR Sequence***

> Table 15 shows the BUFR sequence for *clouds*. In BUFR, how the data
> is depicted is not specified. Only the points describing the line and
> the attributes associated with that line are held.

  --------- -------- -----------------------------------------------------
                     **GFA Clouds**

  3 16 066  3 16 050 GFA header

            1 12 000 Replicate 12 descriptors (Number of replications =
                     Number of areas of clouds)

            0 31 001 Replication count

            3 01 023 Latitude, longitude

            0 08 007 Dimensional significance, 3=Volume

            2 04 001 Add associated field

            0 31 021 Associated field significance, 21: 0=original value,
                     1=substituted/corrected value

            1 01 000 Replicate 1 descriptor

            0 31 001 Replication count

            3 01 027 Description of feature

            0 20 008 Cloud distribution for aviation, 3=Broken, 4=Overcast

            0 20 013 Height of base of cloud

            0 20 014 Height of top of cloud

            2 04 000 Add associated field, Cancel

            0 08 007 Dimensional significance, Missing=Cancel

            0 08 021 Time significance, Missing=Cancel
  --------- -------- -----------------------------------------------------

> **Table 14: GFA Clouds BUFR Sequence**

2.  ***Feature Header***

3.  ***Feature Data***

```{=html}
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```
8.  **Contact Details**

> The Aviation Weather Center can provide a consultancy service to
> assist individual clients in the construction of GFA visualization
> software that is fully compliant with ICAO Annex 3 and the software
> criteria that have been constructed by the ICAO SADIS Operations
> Group. Please contact the Aviation Weather Center via the contact
> details below for further information.

Clinton E. Wallace

> Chief, Aviation Support Branch

Aviation Weather Center (NOAA/NWS/NCEP)

7220 NW 101st Terrace, Room 101

Phone: 816.584.7248

Fax: 816.880.0650

Email: Clinton.Wallace@noaa.gov