Getting it Right
The Graphical Area Forecast
(GAF) Working Group included
representatives of just about
everyone who has an interest in
low-level aviation weather. The
core group included people from
Airservices Australia, CASA, the
Australian Defence Force, Bureau
of Meteorology, regional airlines,
GA and airline pilot associations,
sport and gliding organisations.
Meteorologists are a pretty
bright bunch, and they love solving
problems. However, like everyone
they must work within tight
resource constraints, so while we
could ask for almost anything, it
needed to be produced efficiently.
Big questions soon emerged
including what the GAF would
contain and how it might
look, particularly in relation
to symbology, abbreviations,
formatting, distribution and
updates.Okay... So,
what’s a GAF?
From 9 November 2017 (and
probably by the time you read
this), the 28 existing ARFORs are
replaced by ten GAFs. These are
broadly state-based, with separate
east-west, or north-south divisions
of the larger states, and each fits
on a single page.The title block contains the
validity period and time applicable
to the position of weather features.
Like the ARFOR, all heights are
given above sea level, and a legend
reminds the reader of essential
facts that link cloud types with
thunderstorms, severe icing and
turbulence.
If you’ve f lown at f light levels
you’d be aware of the SIGWX
charts: the GAF is a similar
concept, but the critical weather
information is localised, more
easily identifiable and tailored for
low-level f light operations.
For a complete weather briefing
it’s critical that pilots also check
SIGMETs and AIRMETs; the
latter providing updates when
conditions worse than forecast
subsequently become expected.
As before, pre-f light planning56 Graphical Weather Forecasts
AUSTRALIAN FLYING November – December 2017A GAF is identified by its state
and division; for example, the
GAF for the northern part of
Western Australia will be known
as WA-N, and for the eastern part
of NSW, NSW-E. Each GAF’s
boundaries are shown on its chart
by heavy boundary lines.
As the name implies, each GAF
is a graphical chart of the area,
divided into sub-areas by wiggly
lines.
Because there is no need for a list
of defining waypoints, there can
be as many sub-areas as needed,
each identified with a letter. The
sub-areas themselves can also be
split where there are variations
in particular phenomena: for
example, the TAS GAF might
contain sub-areas A and B, with
part of B, denoted as B1, containing
a forecast thunderstorm. The chart
shows tropical cyclones, cold fronts
and troughs, “weather features”,
with their direction and speed.
There’s also a remarks box, which
will include forecast weather for
critical locations.
A table adjacent to the chart
maps each sub-area to forecast
surface visibility and weather;
cloud, icing and turbulence; and
freezing level. So that a pilot
can quickly visualise how the
sub-areas will affect their f light,
various place names are shown,
along with critical locations.should always include a check of
applicable NOTAMs.
While the GAF provides much
more weather information, in a
more comprehensible format than
the ARFOR, a GAF won’t tell you
the forecast enroute winds.Grid Point
Enroute Winds
For a long time, forecast winds
for high f light levels have been
presented in boxes, across grid
points on a chart, appropriately
termed Grid Point Wind and
Temperature charts, or GPWT.
To support transition to the
GAF, in November last year the
vertical extent of the ARFOR
was reduced to 10,000 feet, and
consequently, area winds at two
altitudes above 10,000 feet were“ A little time now, before you
next fly, will save a lot of
frustration later on.”
Sample TAS GAF for TasmaniaGPWT Forecasts broadly correspond with GAF
boundaries and are available up to 21 hours in advance.BUREAU OF METEOROLOGY