|The Graphical-AIRMET product, known as the
"G-AIRMET," is a decision-making tool based on weather "snapshots"
displayed at short time intervals. The G-AIRMET identifies hazardous
weather in space and time more precisely than text products,
enabling pilots to maintain high safety margins while flying more
At NOAA, our goal is to maximize aviation safety and air space
efficiency by providing the most accurate and timely weather
information possible to enhance both pre-flight and in-flight
decision making. For decades, NOAA has issued text-based AIRMETs
(Airmen's Meteorological Information) that have provided broad-scale
descriptions of hazardous weather. Often referred to as a time
"smear", the text-based AIRMET requires meteorologists to describe
hazardous weather over large geographical areas for six-hour
periods. G-AIRMET provides more precise, and informative weather
hazard depictions than the text only AIRMET.
Aviation weather users have found that pictures are worth a thousand
contractions. G-AIRMETs provide a better path from the aviation
meteorologist to the weather user, by providing precise, interactive
and easy to understand graphical displays. Meteorologists can put
their energy into creating and updating G-AIRMET weather graphics,
while the traditional text AIRMET is generated from, and completely
consistent with G-AIRMET information.
Snapshots (G-AIRMET): are graphical forecasts of en-route
weather hazards valid at discrete times no more than 3 hours apart
for a period of up to 12 hours into the future (00, 03, 06, 09 and
12 hours). 00 hour represents the initial conditions, and the
subsequent 3-hourly graphics depict the area affected by the
particular hazard at that valid time. G-AIRMET depicts the following
en-route aviation weather hazards:
- Instrument flight Rule conditions (IFR)
- Mountain Obscuration
- Freezing Level
- Low Level Wind Shear (LLWS)
- Strong Surface Winds
|G-AIRMETs are issued every 6 hours and
updated/amended as necessary, coincident with the text AIRMET
products. G-AIRMETs provide additional weather information and
higher forecast resolution than text AIRMET products alone. Since
G-AIRMETs and text AIRMETs are created from the same forecast
"production" process, there exists perfect consistency between the
two. Using the two together will provide clarity of the area
impacted by the weather hazard, and improve situational awareness
and decision making.
and Format: G-AIRMETs can be viewed using the G-AIRMET
display tools at: http://www.aviationweather.gov/products/gairmet/.
A user tutorial (FLASH)
is also available.
|G-AIRMETs are also provided in ICAO recommended
“Binary Universal Form for the Representation of
Meteorological Data” (BUFR) format. This is suitable for the
integration into service provider and user systems. This format
allows service providers or end users to customize G-AIRMET displays
to their specific applications and unique systems. For each G-AIRMET
valid time, the binary message will contain the following:
- En-route weather phenomena (as appropriate)
- Valid time
- Type of message (Normal, Correction, Amendment, and Corrected
- Location of each of the phenomena using geographical
coordinates to delineate the affected areas.
|Click here to learn more about using BUFR
| WMO Headers
|Strong Surface Wind
|Low Level Wind Shear Potential
|Lowest Freezing Levels
|Multiple Freezing Levels
|1) Select parameter by selecting appropriate
button. Note that the button color will change to the color of the
|To deselect ... click on button again ... or
select the button
|2) Select Valid time by clicking on a
"valid time" or moving the button on the slider bar.
to start looping and
to stop looping.
will reset the page.
|Previously, AIRMETs (Airmen’s Meteorological
Information) were regularly scheduled text messages containing a 6
hour forecast with a 6 to 12 hour outlook period. AIRMETs are issued
every 6 hours, where there is a 50% probability that any of the
following en-route weather phenomena will cover an area of
3000 square miles or greater:
- Instrument flight Rule conditions (IFR): Areas
of cloud ceilings with bases less than 1000 feet above ground level
(AGL) and/or areas of surface visibilities below 3 statute miles,
including the weather causing the visibility restriction. The cause
of the visibility restriction includes only PCPN, FU, HZ, BR, FG,
- Mountain Obscuration: Areas of widespread
mountain obscuration where Visual Meteorological Conditions (VMC)
cannot be maintained, including the weather causing the
obscuration. The weather causing the obscuration includes only
CLDS, PCPN, FU, HZ, BR, and FG.
- Icing: Areas of moderate airframe icing, other
than convectively induced, including the areal extent.
- Freezing Level information is included after
AIRMETs for moderate icing or statements indicating that no
significant icing is expected. Freezing level is defined as the
lowest freezing level above the ground or at the SFC as
appropriate. Freezing levels are delineated using high altitude VOR
locations describing the location of the lowest freezing level
above the ground or SFC as appropriate. Freezing levels above the
ground are delineated at 4000 feet intervals above mean sea level
(AMSL). Multiple freezing levels above the ground are delineated
using "BOUNDED BY" followed by high altitude VOR locations. The
range of freezing levels across the forecast area is also included.
- Turbulence: Areas of moderate turbulence,
other than convectively induced, including the vertical extent.
- Low Level Wind Shear (LLWS): LLWS is defined
as wind shear below 2000 feet AGL, other than convectively induced,
exceeding 10 knots per 100 feet (vector difference between two
points in space). LLWS potential information is included after
AIRMETs for moderate turbulence and/or sustained surface winds
greater than 30 knots or statements indicating no significant
turbulence is expected. LLWS Potential information includes the
list of affected states, and the phrase "BOUNDED BY" followed by
high altitude VOR locations to delineate the area affected.
- Strong Surface Winds: Areas of sustained
surface winds greater than 30 knots. The direction and speed of
winds are not be depicted; only the area where sustained surface
winds greater than 30 knots will occur.
|AIRMETs are prepared four times daily: 0300, 0900,
1500, and 2100 Universal Coordinated Time (UTC). The following
information is included in the text AIRMET, as appropriate, and in
the order indicated:
- “AIRMET [NAME]” followed by a list of affected
states or Great Lakes using two-letter abbreviations and/or coastal
- Location of the phenomenon using a series of high altitude VORs
to delineate the affected area.
- En-route weather phenomena which may affect the safety of
aircraft operations as described above.
- Beginning and/or ending times of phenomena if different than
the AIRMET bulletin times. The practice of including trend remarks
is discontinued with the implementation of the G-AIRMET.
- Information describing when the weather the phenomena will end
during the 6 hour valid time or during the 6 to 12 hour outlook
period or continue through the outlook period.
- In the AIRMET 6 to 12 hour outlook, the affected area is
described using “BOUNDED BY” followed by a series of
high altitude VORs.
- SIGMET (Significant Meteorological Information) references are
included in AIRMETS using the format “SEE SIGMET
of AIRMETs (pdf)
| What is the difference between the
3-hourly G-AIRMET graphics and the former “AIRMET”
|The former “AIRMET” depictions were 6
hour "time-smeared" area of the text AIRMET. G-AIRMET graphics are
created and valid at 3 hour increments. You can find more
information at G-AIRMET Presentation (March 2010) (pdf)
| Why is the G-AIRMET valid at 6 hours
smaller than the 6-hour AIRMET text?
|As described in the previous question, the G-AIRMET
valid at 6 hours is an areal depiction (snapshot) of that weather
hazard as it is expected to exist at that moment (i.e. 6 hours from
issuance). The 6-hour AIRMET text from line, (valid for the 00-06
hour time period) is a description of the entire area that weather
hazard will affect over a 6 hour period.
| Why do we have both G-AIRMETs and the
old text AIRMETs?
|Eventually, G-AIRMETs will replace AIRMET text
products. While the G-AIRMET is able to better depict the weather
hazard and its position over time, it can not be “read”
over radio broadcasts and by briefers. Because of this, a
requirement will continue to exist for a text version of en-route
aviation weather hazards. The BUFR file-format of the G-AIRMET
contains both graphic and “attribute” information, from
which text can be derived, or “formatted”. Until this
text portion of G-AIRMET can be tested and proved to meet safety of
flight standards, both G-AIRMETs and legacy text AIRMETs will be
produced. Remember, currently the legacy text AIRMET and G-AIRMET
are both created by the AWC from the same production process, so
there will always be consistency between them.
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