Graphical sigmets – a useful aid to situational awareness

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The Bureau of Meteorology will begin issuing graphical representations of their text SIGMETs on 29 May 2014.

They will help extend pilots’ situational awareness, but the text SIGMET must continue to be used for flight planning purposes.

The geographical coverage of the graphical product will be the same as for the text product, and is limited to those areas in the Australian flight information regions (FIRs) listed in AIP Book GEN 3.5 sections 5.1.9-11.

The following three graphics will be automatically generated and issued every ten minutes, as well as when a text SIGMET is issued:

  • Low-level SIGMETs (affecting airspace below FL100)
  • High-level SIGMETs (affecting airspace above FL100)
  • All-level SIGMETs

There will be a slight delay between the issue of the text SIGMET and the subsequent update of the graphic.

Users are to consider the product as being valid only for the time of issue. Therefore, users need to ensure they are looking at the latest product (the issue time is shown in the bottom left-hand corner of the graphic).

The graphics will be issued even if there are no text SIGMETs current.

When the vertical extent of a phenomenon crosses FL100, the SIGMET will be shown on both the low-level and high-level graphics.

Two SIGMETs will be displayed for one phenomenon when:

  • an extended (EXTD) SIGMET is first issued and the previous SIGMET (for the same phenomenon) is yet to expire
  • a (NEW) SIGMET is first issued in response to a significant change to an event given in a previous SIGMET, and the previous SIGMET is yet to be cancelled.

If a text SIGMET cannot be rendered graphically, it will be displayed in text format on the graphic. An example of each of the three graphics (low, high and all) is given below. The associated text SIGMETs are given after the graphics.

Low-level graphical SIGMET
Low-level graphical SIGMET
High-level graphical SIGMET
High-level graphical SIGMET
All-level graphical SIGMET
All-level graphical SIGMET

YMMM SIGMET B01 VALID 240040/240440 YMHF –

YMMM MELBOURNE FIR SEV TURB FCST WI LRP – LKEC – 4300S 14900E – SEC – YMSY SFC/8000FT STNR INTSF
RMK: ME NEW

YMMM SIGMET J06 VALID 232145/240145 YPRF –
YMMM MELBOURNE FIR EMBD TS FCST WI S2500 E12400 – S2350 E11840 – S2110 E11600 – S1958 E12100 – S2130 E12820 TOP FL450 STNR NC
RMK: MW EXTD J05 201745/202145 SEE ALSO I06

YBBB SIGMET I06 232145/240145 YPRF –
YBBB BRISBANE FIR EMBD TS FCST WI S2500 E12400 – S2350 E11840 – S2110 E11600 – S1958 E12100 – S2130 E12820 TOP FL450 STNR NC
RMK: BN EXTD I05 201745/202145 SEE ALSO J06

YBBB SIGMET H06 VALID 232158/240158 YMMC-
YBBB BRISBANE FIR SEV ICE FCST WI S3000 E12200 – S2500 E11800 –
S2500 E12800 – S2000 E13700 – S2400 E13600 – S3000 E13000 FL140/230 STNR NC
RMK: BN EXTD H05 201758/202158 SEE ALSO YMMM E06=

YMMM SIGMET E06 VALID 232158/240158 YMMC-
YMMM MELBOURNE FIR SEV ICE FCST WI S3000 E12200 – S2500 E11800 – S2500 E12800 – S2000 E13700 – S2400 E13600 – S3000 E13000 FL140/230
STNR NC
RMK: MM EXTD E05 201758/202158 SEE ALSO YBBB H06=

Each polygon describing the horizontal extent of the event will be accompanied by a box giving other information included in the text product. A decoding of the information in the westernmost box in the graphics above is:Decoding of the phenomenon symbols used in the SIGMET graphics

A full decoding of the phenomenon symbols used in these graphics can be found in AIP Book GEN 3.5 section 23.

Visit the Bureau of Meteorology’s Aviation Weather Service for more information.

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