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Graphical Area Forecast (FA) Experiment Help
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| BACKGROUND |
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The Federal Aviation Administration (FAA) and National Weather Service have responded to a call from the users of the National
Aerospace System (NAS) for better weather information by collaborating with industry to develop an enroute, aviation weather
product called the Graphical Area Forecast (GFA). The GFA represents the first major shift away from national text-based aviation
weather products to graphical products. The GFA has been designed to replace the information provided by both the current aviation
area forecast (FA) and AIRMET text products. It is expected that a small number of users may not have access to graphical products
for some period into the future, extending the requirement to provide text products. The FAA has proposed that the U.S. adopt the
International Civil Aviation Organization (ICAO) GAMET area forecast as the standard text format to continue after the GFA becomes
operational. This proposal has been agreed to in principal by a variety of aviation users groups.
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| GFA EXPERIMENT |
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A GFA and GAMET Experiment was carried out at the Aviation Weather Center during December 2003. The first goal of the
Experiment was to generate and archive 10 GFA cases over the western and eastern contiguous United States (CONUS) - 5 in the west
and 5 in the east. The western area covered more than a third of the CONUS, and the eastern area approximately a sixth of the CONUS
( Figure 1). These areas were chosen to because they include both a variety of weather regimes and complex terrain. The Experiment
required that each case contain all of the proposed GFA elements (see below). The vertical domain of the GFA extends from the
surface to approximately 45,000 feet above mean sea level (FL450).
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The second goal of the experiment was to produce GAMET text forecasts for each Air Route Traffic Control Center area (Flight
Information Region - FIR) within the domain of the experiment. Each GAMET was produced by using only the information contained
in the GFA. The GAMET text format is a highly structured form of information, and thus, friendly to computer processing. Section I of
the GAMET (Figure 2) provides hazardous weather information, and Section II (Figure 3) includes other required information.
Sections I and II of the GAMET, taken together, encapsulate all of the required information currently contained in both the FA and
WA products. The proposed GAMET is valid for the first six hours of each GFA. The GAMET generation process for this experiment
was carried out using a manual process. However, it is planned that this process will be automated.
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Each GFA case includes a set of seven “snapshot” forecasts for each element. These forecasts are valid at standard forecast intervals
out to 24 hours (0, 3, 6, 9, 12, 18, and 24). GFA forecasts delineate weather areas precisely in time and space. GAMET text products
were produced from the first three GFA snapshots. The GAMET text tends to give the most conservative or “worst weather”
conditions during the valid period.
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| GFA AND GAMET WEATHER ELEMENTS |
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Hazards:
► sustained surface wind greater than 30 knots
► surface visibility below 3 statute miles - Instrument Flight Rules (IFR)
► significant thunderstorms
► mountain obscuration
► ceiling below 1000 feet above ground (IFR)
► significant towering cumulus cloud (TCU)
► icing
► turbulence
► mountain waves
► low level wind shear
► non-convective SIGMETs
Other Required Information:
► location and expect movement of pressure centers and fronts
► other clouds below FL180 (approximately 18,000 above mean sea level)
► surface visibility between 3 and 5 statute miles - marginal visual flight rules (MVFR)
► freezing level
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| GRAPHICAL ADVANTAGE |
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AWC meteorologists use state-of-the-art guidance information to determine graphical snapshot forecast areas. In Figures 4a, 4b, and
4c, icing guidance is shown with a GFA icing forecast snapshots (white solid lines). Figure 4a shows a mature icing area that is
forecast over northern Idaho and northwest Montana. In Figure 4b, this mature area has diminished, and a new icing area is
developing over north-central Montana along the Canadian border. However, none of the icing is significant at this point in time, and
no GFA icing area is forecast. In Figure 4c, the new area has continued to develop and is now a new GFA icing element. In each case
the precise icing forecast area is delineated, or left out as required.
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In contrast, Figure 4d shows the area delineated by the traditional AIRMET text for the same time 6-hour time period. The GFA
snapshot forecasts are shown inside the AIRMET area for illustration purposes. The AIRMET product is a temporal and spatial smear,
and does not include information about when or where the icing will occur at any give time
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Figure 1 - GFA/GAMET Experiment areas
Figure 2: GAMET Section I - Hazards
Figure 3: GAMET Section II - Other required information
Figure 4a: The GFA forecast depicts the precise area for 00 hour forecast.
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Figure 4b: The GFA forecast depicts the precise area for the 03 hour forecast.
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Figure 4c: The GFA forecast depicts the precise area for the 06 hour forecast.
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Figure 4d: The current AIRMET text product covers the largest possible area for the entire 6 hour forecast period.
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