AIRMET, SIGMET, and CWA: In-Flight Weather Advisories Explained

Airport reports and forecasts cover the ends of a flight; advisories cover the middle. This page explains each advisory and decodes a SIGMET and a Convective SIGMET from the FAA Aviation Weather Handbook. The rules come from NWS Instruction 10-811, the directive U.S. watch offices issue advisories under, plus the Handbook and the AIM [1][2][3].

What are the in-flight weather advisories?

"There are four types of inflight aviation weather advisories: the SIGMET, the Convective SIGMET, the AIRMET, and the Center Weather Advisory (CWA)." [3, para. 7-1-6] SIGMETs and AIRMETs come from the three U.S. Meteorological Watch Offices: the Aviation Weather Center, the Alaska Aviation Weather Unit, and WFO Honolulu [1, paras. 26.2.1 and 26.3.1]. Of everything forecasters send pilots, "SIGMETs are of highest priority among all meteorological products provided to aviation users." [2, sec. 2]

Who issues each advisory, and what it covers:

When each advisory is valid and issued:

Altitudes in advisories are MSL, written in hundreds of feet, with FL at 18,000 ft and above [2, sec. 4].

SIGMET

"A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena that may affect the safety of aircraft operations." [1, para. 26.2] Over the CONUS a non-convective SIGMET is issued for severe or greater turbulence, severe icing, dust storms, sandstorms, and volcanic ash [2, sec. 6.1.1]. It is unscheduled, valid up to four hours, and reissued at least every four hours while conditions continue [2, sec. 6.1.2]. Outside the CONUS, SIGMETs also cover thunderstorms and tropical cyclones, and can run six hours for volcanic ash and tropical cyclones [2, sec. 6.3.1][1, para. 26.2.5.2].

A decoded SIGMET

Here is the Handbook's sample, printed exactly as in the FAA Aviation Weather Handbook [1, para. 26.2.4.1.3]. It is a teaching example, not a live advisory. Hover, focus, or tap any group.

Scroll sideways to see the full line.

SFOR UWS 100130
SIGMET ROMEO 1 VALID UNTIL 100530
OR WA
FROM SEA TO PDT TO EUG TO SEA
SEV TURB BTN FL280 AND FL350. CONDS CONTG BYD 0530Z.

Official sample non-convective SIGMET, FAA Aviation Weather Handbook (FAA-H-8083-28B), Figure 26-4 [1, para. 26.2.4.1.3]. "SFOR" is the area identifier SFO plus the series letter R.

Group by group. "Handbook Table 26-1" is quoted exactly from the Handbook's decoding table; "Plain English" is ours, with the rule behind it cited.

In short, the Handbook's own decode: "Severe turbulence between FL280 and FL350. Conditions continuing beyond 0530Z." [1, para. 26.2.4.1.3] A graphic of the polygon helps, but "a graphical depiction of the SIGMET area is not the entire SIGMET"; read the text for altitudes and movement [1, para. 26.2].

Convective SIGMET

"Convective SIGMETs are issued for the CONUS instead of SIGMETs for thunderstorms. Any Convective SIGMET implies severe or greater turbulence, severe icing, and LLWS." [1, para. 26.2.4.2] The Aviation Weather Center issues one when any of these is occurring or expected [2, sec. 6.2.1]:

• A line of thunderstorms at least 60 miles long, with storms affecting at least 40 percent of its length.
• An area of active thunderstorms covering at least 40 percent of the area, with very strong radar reflectivity or a significant satellite or lightning signature.
• Embedded or severe thunderstorms expected for more than 30 minutes of the valid period, whatever the area.

A special Convective SIGMET may follow a reported tornado, hail of 3/4 inch or more, or gusts of 50 knots or more [2, sec. 6.2.2]. Bulletins go out hourly at 55 past for the East, Central, and West regions, each valid two hours or until superseded, with a 2- to 6-hour outlook at the end [1, paras. 26.2.4.2.3 and 26.2.4.2.5].

Watch the polygon. It is a snapshot at issuance, and fast-moving storms "will very likely end up outside the SIGMET polygon by the end of the hour". The Handbook says the polygons "should only be used for strategic planning" [1, para. 26.2.4.2].

A decoded Convective SIGMET

Scroll sideways to see the full line.

MKCC WST 221855
CONVECTIVE SIGMET 20C
VALID UNTIL 2055Z
ND SD
FROM 90W MOT-GFK-ABR-90W MOT
INTSFYG AREA SEV TS MOVG FROM 24045KT. TOPS ABV FL450. WIND GUSTS TO 60KTS RPRTD. TORNADOES…HAIL TO 2 IN… WIND GUSTS TO 65KTS POSS ND PTN.

Official sample Convective SIGMET, FAA Aviation Weather Handbook, Figure 26-6, transcribed from the figure image [1, para. 26.2.4.2.4]. The Handbook wraps line 6 across four printed lines; it is shown here as one line.

"Handbook meaning" is quoted exactly from Table 26-2 or the Handbook's line-by-line decode that follows it; "Plain English" is ours.

AIRMET

NWS Instruction 10-811 defines an AIRMET as an advisory for en route weather "that may affect the safety of aircraft operations, but at intensities that do not meet SIGMET criteria" [2, sec. 2]. It is issued for [2, sec. 7.1]:

• Ceiling less than 1,000 ft and/or visibility less than 3 SM (IFR), and widespread mountain obscuration. These make up AIRMET Sierra.
• Moderate turbulence, "Sustained surface wind greater than 30 knots (STG SFC WND)." and non-convective low-level wind shear potential below 2,000 ft AGL. These make up AIRMET Tango.
• Moderate icing, with freezing levels. These make up AIRMET Zulu.

Series names from the Handbook [1, para. 26.3.1.2]. Its Tango entry says 30 knots or greater; this page follows the directive's greater than 30 knots, as the Handbook's criteria list does [1, para. 26.3.1.3][2, sec. 7.1].

In Alaska and Hawaii, AIRMETs are still plain text. Alaska bulletins go out every eight hours and Hawaii's every six, and in both states AIRMETs are broadcast on air traffic frequencies [2, sec. 7.2][1, para. 26.3].

G-AIRMET

"The G-AIRMET, a graphical version of the AIRMET, is issued for the same criteria as AIRMETs but are more temporally and spatially precise." [2, sec. 7] Snapshots are valid 0, 3, 6, 9, and 12 hours out, and only the Aviation Weather Center issues them [2, sec. 7]. The directive's September 2, 2025 revision lists "Removed CONUS AIRMET" among its changes, and says XML G-AIRMET products "will become the primary format as the FAA retires the CONUS AIRMET" [2, Summary of Revisions and sec. 7.3]. The Handbook and the AIM still describe a CONUS text bulletin alongside the graphics [1, para. 26.3.1.1][3, para. 7-1-6]; this page follows the newer directive.

The key rule is what happens between snapshots. "The user should assume the hazardous weather condition is occurring between the snapshots unless informed otherwise." If the 00-hour snapshot is clear, the 03-hour shows a hazard, and the 06-hour is clear again, assume the hazard from just after the 00-hour to just before the 06-hour [1, para. 26.3.1.1]. G-AIRMETs are on aviationweather.gov and FIS-B [1, paras. 26.3 and 26.3.1.1].

Center Weather Advisory (CWA)

"A CWA is a concise description of the occurrence or expected occurrence of specified weather phenomena that meet or approach in-flight advisory (e.g., AIRMET, SIGMET, or Convective SIGMET) criteria." [1, para. 26.4] It comes from the CWSU, NWS meteorologists at an FAA air route traffic control center [1, para. 26.4.1][4, sec. 5.2]. A CWA fills gaps where no other advisory is in effect, or supplements one, for example when a hazard has grown beyond its boundary [1, para. 26.4.2][4, sec. 5.2]. CWAs are valid for up to two hours [1, para. 26.4.1], and "By nature of its short lead time, the CWA is not a flight planning product." [3, para. 7-1-6] The Handbook's example from the Denver center decodes in part as "Isolated severe thunderstorms near Farmington moving northeastward at 10 kt." [1, para. 26.4.3]

Where can you see every advisory field and criterion?

Source conflicts, noted. Where the Handbook or AIM differ from NWS Instruction 10-811 of September 2, 2025, this page follows the newer directive. That covers the CONUS text AIRMET, the Tango wind threshold, and the Hawaii and Alaska AIRMET times (the Handbook lists Hawaii at 0400, 1000, 1600, and 2200 UTC). The Handbook [1, paras. 26.3.1.1 to 26.3.3], NWS Instruction 10-811 [2, secs. 7.1 and 7.2], and the AIM [3, para. 7-1-6] give different freezing-level intervals, so none is stated here. The Convective SIGMET criteria follow the directive and the Handbook; the AIM lists an older set.

Where do advisories mislead pilots?

• The polygon is bigger than the weather. If the area is very large, "only a small portion of this total area would be affected at any one time" [3, para. 7-1-6]. That cuts both ways: it isn't all bad, and you can't know which part is.
• Convective polygons move. They are snapshots at issuance; use the movement in the text [1, para. 26.2.4.2].
• Snapshots have gaps. Assume a G-AIRMET hazard between its snapshots [1, para. 26.3.1.1].
• No advisory is not no hazard. CWAs exist because hazards appear where no advisory is in effect [1, para. 26.4], and a single pilot report can influence a forecaster's decision to issue one [7].
• Older references lag. Some handbooks and apps still show the CONUS text AIRMET. Check dates.

How do you use advisories in a go/no-go decision?

The decision is yours as pilot in command. A few habits:

• Check the whole route at your altitude and time. Step through every G-AIRMET snapshot that covers your flight, not just the first.
• Treat a Convective SIGMET as severe weather. It implies severe turbulence and icing whatever its text says [1, para. 26.2.4.2]. Read the outlook for the next 2 to 6 hours [1, para. 26.2.4.2.5].
• Compare with reports. PIREPs show whether a forecast hazard is actually there (PIREP guide), and METARs and TAFs cover the airports (METAR guide, TAF guide).
• Write it down. A FRAT records the hazards you found [9, ch. 3].

Where do advisories fit in a disciplined decision?

PlaneWX is decision support for general aviation pilots, built around one idea: "Fly like it's your job." Treat the weather decision the way a professional crew would, with the same process every time. That process is a loop: Brief, then FRAT, then Fly or Stay, then Debrief, with a Mentor if you want one. Advisories are part of the Brief. Here's how PlaneWX handles them, as described in the help center [8]:

• Brief: what's on your route. The AIRMETs and SIGMETs section shows advisories that intersect your route corridor and altitude; PlaneWX "uses polygon-based intersection testing for G-AIRMETs and filters by altitude to show only advisories relevant to your flight" (Understanding Briefings). Flights below 18,000 ft see products based below 18,000 ft (Weather Decisions).
• Brief: how they score. An active Convective SIGMET valid during your flight is a 50-point deduction and a non-convective SIGMET along the route is 15. An on-route IFR G-AIRMET is a hard stop for a VFR trip, with a narrow arrival exception. Advisories that end before your flight don't count (How Scoring Works).
• Brief: moving storms. For Convective SIGMETs, time-aware encounter scaling compares storm motion with your track, so a polygon you are flying away from isn't treated like one you'll fly through (Hazardous Weather). CWAs appear too (Hazardous Weather).
• Brief: fresh data. In the final hour, a live fetch pulls SIGMETs, AIRMETs, and G-AIRMETs straight from the Aviation Weather Center (Auto-Refresh).
• FRAT. The flight risk assessment opens within 4 hours of departure, and your own ratings drive it (FRAT).
• Fly or Stay. "PlaneWX never recommends GO or NO-GO. You make the call as PIC." (The Risk Loop)
• Debrief. Self Debrief looks back at the flight, a good time to check whether the advisories matched what you found. It is a PlaneWX Labs feature for Pro Plus (The Risk Loop).

The help center is plain about the limits: "PlaneWX is not a substitute for a complete, independent pre-flight weather briefing. Pull one from a source you already trust before you fly." (The Risk Loop)

See which advisories touch your next route in a PlaneWX briefing, or read how PlaneWX detects hazardous weather. Related: icing analysis, turbulence analysis, convective scoring, the PlaneWX glossary, and live radar in the convective score. G-AIRMETs are U.S. only; international SIGMETs are supported (FAQs).

This page explains published NWS and FAA guidance. The advisories shown are official teaching examples from the FAA Aviation Weather Handbook, not live advisories. Always get a current briefing before you fly.