AIRMET vs SIGMET: G-AIRMETs, PIREPs and Storms

This guide focuses on US student-pilot study and the contiguous states, often called CONUS. The hero is a conceptual weather-study room, not an actual advisory display. Examples below are original practice scenarios, not current weather or a flight recommendation.

What are the key differences at a glance?

Separate a pilot observation from a forecast advisory, then identify the particular hazard.

These are complementary products. A report of good conditions at one point does not erase an advisory covering a larger area or a later period.

What changed from AIRMETs to G-AIRMETs?

For the contiguous US, the current product is the graphical AIRMET, not the retired traditional text bulletin.

The NWS retirement notice set the change for January 27, 2025. It preserved G-AIRMET service; the AWC's current data documentation confirms that CONUS text AIRMETs were discontinued. This was a format transition, not the disappearance of the underlying hazards.

You will still encounter the names Sierra, Tango and Zulu in training and product descriptions. Keep their meanings, but do not look for an old CONUS text bulletin as the only source. Alaska and Hawaii have different product arrangements; do not copy the CONUS format and timing assumptions to every region.

G-AIRMET forecasts are time snapshots. Inspect the sequence relevant to departure, climb, cruise and arrival rather than treating a single selected frame as a statement about the entire day.

What do Sierra, Tango and Zulu describe?

The three names organize hazards; none is a rating of how comfortable your particular airplane will be.

The NWS product-name registry defines these families. Current NWS criteria include ceilings below 1,000 feet and/or visibility below 3 statute miles, widespread mountain obscuration, moderate turbulence, moderate icing, sustained surface wind greater than 30 knots and non-convective low-level wind-shear potential below 2,000 feet AGL. AGL means above ground level.

Read the phenomenon actually selected. A freezing-level line by itself is not a statement that ice was encountered everywhere along that line. Likewise, a turbulence layer aloft does not describe the surface wind at an airport. The AWC product descriptions explain these separate layers.

Original study comparison for the contiguous US. Product names identify different information, not a sequence of permissions to fly.

For the reported ceiling itself, return to the ceiling and visibility guide. Do not confuse an advisory threshold with the weather minimums applicable to a particular operation.

How is a SIGMET different from a Convective SIGMET?

In CONUS, non-convective SIGMETs and Convective SIGMETs separate significant non-thunderstorm hazards from qualifying thunderstorm hazards.

The AWC guide lists severe icing, severe or extreme turbulence, dust or sand storms restricting visibility below 3 miles, and volcanic ash for domestic non-convective SIGMETs. They concern all aircraft categories; “not convective” does not mean mild.

Convective SIGMET criteria include qualifying lines or areas of thunderstorms and embedded or severe storms. Special-issuance criteria include tornadoes, hail at least 3/4 inch in diameter or wind gusts at least 50 knots. Those aviation-product thresholds are not a general definition of every public severe-thunderstorm warning (NWSI 10-811, section 6.2).

A Convective SIGMET implies severe or greater turbulence, severe icing and low-level wind shear. The label is not reserved for a storm that meets only a surface-wind or hail test. Embedded storms can qualify, so “I cannot see an isolated towering cloud” is not a way to dismiss the product (FAA AIM 7-1-6).

How long do these advisories remain valid?

Use the product's actual issue and valid times, and check whether a newer issuance superseded it.

The current NWS instruction, sections 6.1.2, 6.2.3 and 7, supplies these distinctions; the AWC G-AIRMET guide describes the snapshot sequence. Do not turn a six-hour issuance cycle into an assumption that one polygon describes all six hours unchanged. Oceanic, Alaska, Hawaii and tropical-cyclone products can have different rules and are outside this table's scope.

The time a page was opened, the time a product was issued and the time its forecast applies answer different questions. For a hypothetical 1800Z passage through an area, first identify the applicable forecast frame or bulletin; then ask whether it is still the latest available information. A morning screenshot alone cannot answer that.

What does a PIREP add to the forecast?

A PIREP adds a report of what a pilot encountered, with context that a broad forecast cannot replace.

The FAA Flight Service guidance distinguishes routine UA reports from urgent UUA reports and identifies fields such as location, UTC time, altitude/flight level, aircraft type and reported weather. A severe-turbulence report is one example requiring urgent classification; routine does not mean irrelevant.

Read a hypothetical report of light turbulence from a larger aircraft at 12,000 feet at 1510Z alongside a planned light-airplane flight at 4,500 feet at 1800Z. It supplies useful evidence, but it does not directly describe that airplane, altitude or later time. The mismatch is the lesson; neither altitude is a recommended route.

Use PIREPs to compare observations with forecasts, and investigate disagreements rather than choosing whichever sounds more favorable. When reporting conditions, relay what and where you encountered them to ATC or Flight Service when workload permits; do not delay useful information while trying to perfect the coded format (AIM 7-1-18).

Original study workflow. Matching a forecast to a route supports further evaluation; it does not establish a safe or legal flight.

Does an advisory polygon make the decision for you?

No: an advisory is weather information to evaluate, not an ATC clearance or a complete go/no-go decision.

In the AWC GFA help, the display can filter PIREPs by age, altitude, range and type, and different forecast tabs show different advisory layers. Open the product details and verify the layers and time selected before interpreting an apparently empty area. A hidden or filtered layer is not evidence of good weather.

Consider an original study case: your route crosses a Tango turbulence area only during descent. Looking solely at the cruise altitude could miss the relevant part of the trip. Record the overlap, consult the full briefing and instructor, and reconsider timing or routing without assuming an unverified alternate is safe.

For a flight away from an airport's vicinity, 91.103 includes weather reports and forecasts in the required preflight information. 91.9 requires compliance with the aircraft's applicable operating limitations. An advisory's intensity name does not expand those limitations or your qualifications.

Check yourself

These original questions are study exercises, not released FAA questions.

Frequently asked questions

Are AIRMETs only for small airplanes?

No. They inform all pilots, with particular relevance to VFR operations and sensitive aircraft. Lower intensity than a SIGMET does not make a hazard acceptable for a training airplane.

Does every thunderstorm receive a Convective SIGMET?

No. Product issuance criteria are specific. The absence of a Convective SIGMET is not a statement that every thunderstorm is safe to approach or cross.

Does an urgent PIREP replace a SIGMET?

No. An urgent pilot observation and a forecast advisory serve different purposes. Read both, including their time, location and altitude context.

Can a clear airport METAR cancel an en route advisory?

No. An airport observation and a broader en route advisory cover different information. A clear departure field does not describe the full route or a later arrival.

What should you study next?

Use the METAR weather-reports hub for airport observations, the TAF guide for terminal forecast changes, and the ceiling and visibility guide to keep weather quantities distinct. For each practice scenario, name the product, its relevant time and altitude, and the question it leaves unanswered.

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Sources and review notes

• FAA AIM 7-1-6 and 7-1-18: advisory purpose and PIREPs.
• FAA Flight Service, Chapter 8: PIREP classification and fields.
• NWSI 10-811, September 2, 2025: current issuance criteria and timing; NWS CONUS text-AIRMET retirement notice: the 2025 format change.
• AWC product guide, current data documentation and GFA help: product layers, current availability and display context.
• NWS AIRMET family registry: Sierra, Tango and Zulu.
• 14 CFR 91.103 and 91.9: preflight information and aircraft limitations.

Facts checked October 20, 2026. Examples and graphics are original teaching material. Human technical review remains pending before publication.

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