The G-AIRMET, the Graphical Advisory That Replaced the Text Format Most Students Were Trained On, and the SIGMET Threshold That Separates a Caution from a Ground Stop

Many student pilots complete a weather briefing, find no text AIRMETs, and conclude the route is clear - when active advisories are actually present. In 2022, the FAA and Aviation Weather Center retired the old text-based AIRMET format and transitioned entirely to the G-AIRMET (Graphical AIRMET). Training materials and briefing apps haven’t fully caught up, and the gap is showing up in student weather analysis every day.

What Is the G-AIRMET and Why Did the FAA Replace the Text Format?

An AIRMET (Airman’s Meteorological Information) is a weather advisory issued by the Aviation Weather Center in Kansas City for aircraft that lack advanced weather equipment, deicing capability, or significant power margins. Think Cessnas, Pipers, and light twins - the general aviation fleet.

The old text AIRMET described affected areas using place names and coordinate strings. A typical advisory might say “from Memphis to Birmingham to Atlanta,” leaving the pilot to mentally construct a polygon over unfamiliar geography. For experienced pilots with regional knowledge, this was workable. For students flying an unfamiliar route, it was guesswork.

The G-AIRMET draws that polygon for you. It is a visual layer on a map, showing exactly which airspace is affected, during which time windows, and at which altitudes. There is no coordinate decoding. The picture is in front of you.

What Are the Three G-AIRMET Types and What Do They Cover?

The three hazard categories from the old system carried over into the graphical format:

Sierra covers instrument flight rules conditions: ceilings below 1,000 feet, visibility below 3 miles, or mountain obscuration. A Sierra advisory on a VFR cross-country route means the forecast is for conditions below the minimums that make the flight legal.

Tango covers turbulence: moderate turbulence, sustained surface winds above 30 knots, or low-level wind shear below 2,000 feet AGL.

Zulu covers icing: moderate icing, or freezing levels significant to aircraft not certified for flight in known icing conditions.

Where Do I Find G-AIRMETs?

The authoritative source is aviationweather.gov, the Aviation Weather Center’s public-facing site. Under the weather briefing tools, navigate to the Advisories section. SIGMETs and G-AIRMETs appear as separate map layers you can toggle on independently.

Briefing apps are useful planning tools - they are not the regulatory standard. Some apps have gaps in how they surface G-AIRMET data, and a result of “none found” may reflect a display limitation, not an absence of advisories. When the flight matters, check the authoritative source directly.

How Do I Read the G-AIRMET Map Interface?

When you load the G-AIRMET layer, shaded regions appear over the map corresponding to each hazard type. The critical feature is the time-step function: you can advance through the forecast period hour by hour and watch how hazard areas are expected to expand, contract, or shift position.

G-AIRMETs are issued every three hours and forecast out to 12 hours. You will typically see a series of time slices - one covering the next three hours, another covering three to six hours, and so on. The time slice you care about is the one that covers when you will actually be in that airspace, not when you are sitting at the computer.

Clicking on a hazard region gives you the details: hazard type and altitude range. A Zulu advisory might read from the surface to 12,000 feet. A Tango advisory might read from 8,000 feet to Flight Level 180. Sierra advisories are typically surface-based and describe the horizontal area where IFR conditions are forecast.

How Do I Analyze G-AIRMET Altitudes Correctly?

All G-AIRMET altitudes are listed in feet mean sea level. The question you need to answer is not “does an advisory exist?” - it is “does this advisory intersect my planned cruise altitude?”

Consider two scenarios with the same VFR cross-country at 4,500 feet:

In the first, a Zulu advisory shows moderate icing from the surface to 10,000 feet along the route. A standard Cessna 172 with no deice equipment is flying directly through that advisory. That is a no-go.

In the second, the Zulu advisory shows moderate icing from 9,000 feet to Flight Level 180. The same aircraft at 4,500 feet is entirely below the advisory boundary. The conditions may still be worth monitoring - temperature gradients matter - but the pilot now understands where the hazard begins and can make an informed decision.

On a checkride, an examiner is not satisfied with “there is icing in the area.” The expected answer walks through the altitude range, compares it to the planned cruise altitude, and addresses whether the aircraft is equipped for known icing conditions.

What Is a SIGMET and How Does It Differ From a G-AIRMET?

A SIGMET (Significant Meteorological Information) is issued when conditions are severe enough to be hazardous to all aircraft, not just light general aviation. The threshold gap between the two products is significant:

• Where a G-AIRMET covers moderate turbulence, a SIGMET covers severe or extreme turbulence.
• Where a G-AIRMET covers moderate icing, a SIGMET covers severe icing.

Think of a G-AIRMET as a caution and a SIGMET as a consequence.

What Are the Issuance Thresholds for Each Type of SIGMET?

There are two categories.

Convective SIGMETs are issued for:

• An area of thunderstorm activity covering at least 3,000 square miles
• A line of thunderstorms at least 60 nautical miles long
• Embedded thunderstorms
• Severe or extreme turbulence and severe icing associated with convective weather

Convective SIGMETs are numbered sequentially by region - east, central, and west - and carry a valid window of two hours.

Non-convective SIGMETs cover severe or extreme turbulence from non-thunderstorm sources, severe icing not associated with thunderstorms, and phenomena such as volcanic ash or widespread dust storms reducing visibility below 3 miles. These are valid for up to four hours; volcanic ash advisories can extend to six hours.

One important distinction for flight planning: a convective SIGMET is documentation, not a real-time boundary. The weather moves faster than the advisory cycle. The gaps between convective SIGMET polygons are not cleared corridors - cells can be building in those spaces while you are looking for a path through. If a line of convective SIGMETs crosses your route, treat the entire region with deep suspicion.

How Do I Build a Complete Preflight Weather Briefing?

Work from the large scale down to the small scale, building a layered picture of the atmosphere before focusing on your specific route and airports.

1. Synoptic view. Start with the surface analysis chart. Where are the fronts? Is there a low-pressure center within a few hundred miles of the route? Cold fronts bring turbulence, convective activity, and rapid visibility changes behind the line. Warm fronts produce extended regions of low ceilings and reduced visibility as warm air rides up over the cooler air ahead.

2. Significant weather prog chart. This two-panel chart shows forecast significant weather for your time window, identifying areas of expected IFR conditions, turbulence levels, and icing regions in a broad overview.

3. SIGMETs. Are there active convective SIGMETs on or near the route? Where are they moving? Are they expanding or contracting?

4. G-AIRMETs. Add the graphical layers by time slice matched to your planned flight time. For each Sierra, Tango, and Zulu advisory, identify whether it intersects your planned altitude and route.

5. METARs. Pull surface observations at departure, multiple stations along the route, and the destination. Is the atmosphere behaving consistently with the forecast? Significant deviations - colder than expected, ceilings lower than forecast - indicate the models are missing something and your picture needs updating.

6. TAF. Review the terminal forecast at your destination for your expected arrival window. Change groups carry specific meaning: FM (from) means conditions shift at a specific time; TEMPO means temporary conditions lasting less than an hour; BECMG means a gradual transition during a specified period.

7. Winds aloft. Which altitude gives the best combination of groundspeed, ride comfort, and fuel efficiency? Does that altitude place you inside a G-AIRMET hazard area already identified in step four?

8. PIREPs. Has anyone actually been in that air in the past two hours? A pilot report of moderate turbulence from a Cherokee at 8,000 feet over your route is real-world data - the only product written by someone physically in that airspace.

This sequence moves naturally from the synoptic picture to observed conditions, and the G-AIRMET check sits in the middle where it belongs - between the prog chart and the METARs.

One Caution About Advisory Thresholds

G-AIRMETs are issued when conditions are forecast, not necessarily observed. A Zulu advisory for tomorrow morning means the Aviation Weather Center believes icing conditions will be present in that area at that time. Conversely, the absence of a G-AIRMET does not guarantee clean conditions - it means the formal advisory threshold has not been crossed. Marginal conditions exist below that threshold and can still affect a flight.

The practical skill the ACS tests is not whether a pilot can read an advisory. It is whether they can look at a complete weather picture, identify relevant hazards, assess those hazards against the specific aircraft and the pilot’s qualifications, and explain the go/no-go decision out loud.

Key Takeaways

• The text-based AIRMET format was retired in 2022. The G-AIRMET (Graphical AIRMET) is now the standard. Apps that surface text AIRMETs may not display active advisories.
• The authoritative source for G-AIRMETs and SIGMETs is aviationweather.gov. Use the map layers under the Advisories section.
• Always analyze altitude. A G-AIRMET only affects you if it intersects your planned cruise altitude. Know the difference between being inside an advisory and being below or above it.
• A SIGMET represents a higher severity threshold than a G-AIRMET. Moderate turbulence and icing trigger a G-AIRMET; severe or extreme conditions trigger a SIGMET.
• Convective SIGMET polygons are not hard boundaries. Weather between advisories can be building. Treat any line of convective SIGMETs across a route as reason to reconsider the entire corridor.
• Use a structured briefing sequence. Synoptic → prog chart → SIGMETs → G-AIRMETs → METARs → TAF → winds aloft → PIREPs. G-AIRMETs fit naturally in the middle of that process.