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AIRMETs, SIGMETs, and Convective SIGMETs: How to Read Aviation Weather Advisories

Updated: 2 days ago

AIRMETs and SIGMETs are how the aviation weather system warns pilots of conditions that may make a flight hazardous or unsafe. Most pilots learn the broad strokes — Sierra is IFR, Tango is turbulence, Zulu is icing — but few can decode an actual AIRMET text, distinguish a SIGMET from a Convective SIGMET, explain what a CWA is, or describe how to use the graphical G-AIRMET product that has largely replaced the textual format. Understanding all of this is what turns weather advisories from background noise into actionable information that affects your flight decisions.


This post covers AIRMETs, SIGMETs, Convective SIGMETs, and CWAs in practical decoding depth: what each covers, the issuance criteria, validity periods, how to read the text format, the G-AIRMET graphical product, and how to use them for safe flight decisions.



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The Hierarchy of Aviation Weather Advisories

The aviation weather warning system has a hierarchy based on severity:

  • AIRMET (Airmen's Meteorological Information): Less severe weather, but still potentially hazardous especially to small aircraft and GA pilots. Affects large geographic areas. 6-hour validity.

  • SIGMET (Significant Meteorological Information): More severe weather hazardous to all aircraft. Smaller geographic areas. 4-hour validity (6 hours for tropical cyclones and volcanic ash).

  • Convective SIGMET: Specific to convective weather (thunderstorms). Issued hourly, valid 2 hours.

  • CWA (Center Weather Advisory): Short-term advisory issued by ARTCCs (centers) for hazardous weather conditions developing within their area. Used to bridge the gap between forecasts and actual conditions.


Understanding this hierarchy helps you interpret the relative severity and urgency of each advisory.


AIRMETs

AIRMETs cover weather phenomena that affect aircraft below 18,000 feet primarily. They're issued by the Aviation Weather Center (AWC) and cover wide geographic areas. Each AIRMET is valid for 6 hours.


The Three AIRMET Types

AIRMET Sierra (IFR Conditions and Mountain Obscuration)

Issued for:

  • IFR conditions: ceilings below 1,000 feet AGL or visibility below 3 statute miles affecting more than 50% of an area for at least 6 hours

  • Mountain obscuration: clouds, precipitation, or other phenomena obscuring mountainous terrain


When you see Sierra in effect:

  • Plan for IFR conditions in the affected area

  • Mountain VFR may be impractical

  • IFR-rated pilots can typically operate in Sierra conditions

  • Non-IFR pilots should not plan to fly into Sierra-affected areas


AIRMET Tango (Turbulence and Surface Winds)

Issued for:

  • Moderate turbulence

  • Sustained surface winds of 30 knots or more

  • Non-convective low-level wind shear


When you see Tango in effect:

  • Expect bumpy ride in the affected area

  • Strong surface winds at affected airports

  • Plan for crosswind and turbulence

  • Lighter aircraft particularly affected


AIRMET Zulu (Icing and Freezing Levels)

Issued for:

  • Moderate icing in clouds and precipitation

  • Information about freezing levels (altitudes where the freezing point is reached)


When you see Zulu in effect:

  • Significant icing potential in clouds

  • Aircraft without anti-ice equipment should avoid known icing conditions

  • Use freezing level information to plan altitudes that minimize icing exposure

  • Even FIKI-certified aircraft should monitor conditions carefully


Reading AIRMET Text

AIRMETs use a specific format. Here's an example:

WAUS41 KKCI 161645
WA1Y
SLCS WA 161645
AIRMET SIERRA UPDT 1 FOR IFR AND MTN OBSCN VALID UNTIL 162300
AIRMET IFR...UT WY CO ID NV
FROM SLC TO BIH TO 30W BIH TO 30W SLC TO SLC
CIG BLW 010/VIS BLW 3SM PCPN/BR. CONDS CONTG BYD 23Z THRU 05Z.

AIRMET MTN OBSCN...UT
FROM SLC TO 60S SLC TO 60S BIH TO BIH TO SLC
MTNS OBSC BY CLDS/PCPN/BR. CONDS CONTG BYD 23Z THRU 05Z.

Decoded:

  • WAUS41 KKCI — Header indicating issuing office

  • 161645 — 16th day at 1645 Zulu (issuance time)

  • AIRMET SIERRA — Type (Sierra = IFR/Mountain Obscuration)

  • UPDT 1 — First update of the day

  • FOR IFR AND MTN OBSCN — What conditions are being reported

  • VALID UNTIL 162300 — Valid until 16th at 2300 Zulu (6 hours later)

  • AIRMET IFR...UT WY CO ID NV — IFR conditions in those states

  • FROM SLC TO BIH TO 30W BIH... — Bounding the affected area using VOR identifiers (this is a polygon)

  • CIG BLW 010/VIS BLW 3SM — Ceilings below 1,000, visibility below 3 SM

  • PCPN/BR — Due to precipitation and mist

  • CONDS CONTG BYD 23Z THRU 05Z — Conditions continuing beyond 23Z through 05Z (after the AIRMET expires, conditions persist)


Reading the bounding polygon: The "FROM X TO Y TO Z" lines define the area covered by the AIRMET. Each point is typically a VOR identifier or geographic point. The polygon connects all named points. This is the easiest way to determine if your route is affected.


G-AIRMET: The Graphical Product

In June 2020, the FAA changed the AIRMET delivery format. The text-based AIRMETs are still issued, but the primary product is now the G-AIRMET (Graphical AIRMET), which provides:

  • Graphical depiction of affected areas on a map

  • 3-hour intervals showing how conditions are forecast to evolve

  • More precise polygon depictions than the textual VOR-based format

  • Visual layering showing where IFR, turbulence, and icing overlap


How to access G-AIRMETs:

  • Aviation Weather Center website (aviationweather.gov)

  • Most modern EFB apps (ForeFlight, Garmin Pilot, FltPlan Go)

  • 1800wxbrief.com graphical briefings

  • Datalink products (FIS-B, XM Weather)


Why the change matters:

  • Easier to visualize affected areas

  • Time progression shows when conditions move in/out of your route

  • More precise areas (not limited to bounding polygons)

  • Better integration with flight planning tools


For pilots, the practical use:

  • View your planned route on the G-AIRMET map

  • See if IFR, turbulence, or icing affects your route

  • Plan altitude changes around forecasted icing or turbulence

  • Check progression to see when conditions improve


SIGMETs (Non-Convective)

SIGMETs cover severe weather hazardous to all aircraft. They're issued by the Aviation Weather Center as needed (not on a regular schedule) and are valid for 4 hours typically (6 hours for tropical cyclones and volcanic ash).


Conditions warranting a SIGMET:

  • Severe icing not associated with thunderstorms

  • Severe or extreme turbulence not associated with convective activity (e.g., clear air turbulence, mountain wave turbulence)

  • Dust storms or sandstorms lowering surface visibility below 3 statute miles

  • Volcanic ash clouds

  • Tropical cyclones with winds of 64 knots or greater (typically used for hurricane operations)


SIGMET vs. AIRMET key differences:

  • Severity: SIGMET conditions are more severe (severe icing vs. AIRMET moderate)

  • Aircraft affected: SIGMETs affect ALL aircraft; AIRMETs primarily affect light aircraft

  • Validity: SIGMETs are 4 hours; AIRMETs are 6 hours

  • Issuance: SIGMETs are as-needed; AIRMETs are regularly scheduled


Reading a SIGMET:

SIGMET ALPHA 1 VALID 161800/162200
LANDAA: WAUS01 KKCI 161800
SIGMET ALPHA 1 VALID 161800/162200 KKCI-
SLCS SIGMET ALPHA 1 VALID UNTIL 162200
SVR ICE FROM 60WSW BCE TO 60SW DBL TO BCE
WI AREA SVR ICE BTN FRZLVL AND FL180. CONDS DVLPG.
RPRTD BY ACFT.

Decoded:

  • SIGMET ALPHA 1 — Sequential identifier (Alpha sequence, 1st issuance)

  • VALID 161800/162200 — Valid 16th 1800Z to 16th 2200Z (4 hours)

  • KKCI-SLCS — Issuing office

  • SVR ICE — Severe icing

  • FROM 60WSW BCE TO 60SW DBL TO BCE — Polygon defining affected area

  • WI AREA — Within area

  • SVR ICE BTN FRZLVL AND FL180 — Severe icing between freezing level and FL180

  • CONDS DVLPG — Conditions developing

  • RPRTD BY ACFT — Reported by aircraft (means PIREPs triggered the SIGMET)


Convective SIGMETs

Convective SIGMETs specifically address convective weather hazards (thunderstorms). They're issued at H+55 each hour for the next hour, with updates as needed.


Conditions warranting a Convective SIGMET:

  • Severe thunderstorms with surface winds 50 knots or greater

  • Hail at the surface 3/4 inch in diameter or larger

  • Tornadoes

  • Embedded thunderstorms

  • Lines of thunderstorms (squall lines)

  • Areas of widespread thunderstorms affecting more than 40% of an area at least 3,000 square miles


Validity: 2 hours (vs. 4 hours for non-convective SIGMETs)


Reading a Convective SIGMET:

WST CFV 161155
CONVECTIVE SIGMET 35E
VALID UNTIL 1355Z
TX OK AR LA MS
FROM 60WNW DFW-30NE LIT-20E MSY-60SE LBB-40NW JCT-60WNW DFW
LINE TS MOV FROM 27040KT. TOPS TO FL450.
WIND GUSTS TO 60KT...HAIL TO 1 1/2 IN POSS.

Decoded:

  • WST CFV 161155 — Header indicating Convective SIGMET issuing office, 16th at 1155Z

  • CONVECTIVE SIGMET 35E — 35th of the day, Eastern (vs. Central or Western series)

  • VALID UNTIL 1355Z — Valid until 1355Z (2 hours)

  • TX OK AR LA MS — States affected

  • FROM 60WNW DFW... — Polygon defining affected area

  • LINE TS — Line of thunderstorms

  • MOV FROM 27040KT — Moving from 270° at 40 knots

  • TOPS TO FL450 — Tops to flight level 450 (45,000 feet)

  • WIND GUSTS TO 60KT — Surface gusts to 60 knots

  • HAIL TO 1 1/2 IN POSS — Possible hail to 1.5 inches


The two-hour validity is significant: Convective SIGMETs update hourly because thunderstorm conditions change rapidly. Don't rely on a 4-hour-old Convective SIGMET — get current information.


CWAs (Center Weather Advisories)

CWAs are issued by ARTCCs (Air Route Traffic Control Centers) for short-term hazardous weather conditions in their area. They serve to:

  • Alert pilots to immediate hazards

  • Bridge gaps between scheduled forecasts

  • Provide rapid notification of developing conditions


When CWAs are issued:

  • Conditions developing rapidly that haven't reached AIRMET/SIGMET threshold

  • Short-term significant weather expected

  • Localized hazards within a center's airspace

  • Often before formal AIRMETs/SIGMETs catch up


Validity: Typically 2 hours

Format: Less standardized than AIRMET/SIGMET. CWAs are more conversational and specific to local conditions.


Pilot use:

  • Listen to CWAs broadcast on Flight Service or HIWAS

  • Check ATC for any CWAs in your area

  • Treat CWAs as immediate hazards

  • Often the first warning of developing severe weather


Where Pilots Get These Advisories

Pre-flight:

  • 1800wxbrief.com — Standard, abbreviated, and outlook briefings include current AIRMETs, SIGMETs, and Convective SIGMETs

  • aviationweather.gov — Aviation Weather Center website

  • EFB apps (ForeFlight, Garmin Pilot, etc.) — graphical and text products

  • Phone briefing — 1-800-WX-BRIEF specialist provides applicable advisories


In-flight:

  • Flight Watch (122.0): Listening for advisories from Flight Service

  • HIWAS (122.x): Continuous Hazardous Inflight Weather Advisory Service broadcast

  • ATC: Center and approach controllers may issue advisories for traffic

  • Datalink weather: ADS-B FIS-B (free), XM Weather (subscription)

  • EFB apps with cellular or datalink: Real-time updates


How to Use AIRMETs and SIGMETs in Flight Planning

Pre-flight assessment:

  1. Identify all AIRMETs and SIGMETs along your route

  2. Determine which apply to your altitude

  3. Assess severity and your aircraft's capability

  4. Look at validity periods — will the advisory be in effect during your flight?

  5. Plan around hazards when possible


Decision framework:

If a SIGMET is in effect along your route:

  • Severe weather hazardous to all aircraft

  • Strongly consider delay or alternate routing

  • Don't fly into SIGMET conditions even with capable aircraft

  • If you must fly, have multiple alternates and a clear escape plan


If a Convective SIGMET is in effect:

  • Active severe convection

  • Don't fly into the affected area

  • Consider grounding until passage

  • Updated hourly — get current information


If an AIRMET is in effect:

  • Less severe hazards but still significant

  • Assess your aircraft's capability

  • IFR conditions (Sierra) — IFR-rated pilots and aircraft only

  • Turbulence (Tango) — expect bumpy ride

  • Icing (Zulu) — non-FIKI aircraft should not fly in known icing conditions


If a CWA is in effect:

  • Treat as urgent hazard

  • May indicate developing severe weather

  • Watch for escalation to SIGMET


Common Mistakes Pilots Make

1. Ignoring AIRMETs because "they cover the whole country": AIRMETs cover wide areas, but specific portions affect your specific route. Identify whether your route is in the affected polygon.

2. Focusing only on SIGMETs: AIRMET conditions are still hazardous. Moderate icing in a non-FIKI aircraft is still ice that can ground you.

3. Not checking for updates: SIGMETs are 4 hours, AIRMETs are 6 hours, Convective SIGMETs are 2 hours. Conditions change. Get updates throughout the flight.

4. Misinterpreting validity periods: "Valid until 2300Z" doesn't mean conditions disappear at 2301Z. The advisory expires; conditions may persist.

5. Confusing AIRMET and SIGMET severity: AIRMET = moderate, SIGMET = severe. Don't conflate them.

6. Not using G-AIRMETs: The graphical product is much easier to interpret than text. Use it.


Practical Examples

Scenario 1: VFR flight with AIRMET Sierra

  • You planned a VFR flight from KSLC to KSEA. AIRMET Sierra is in effect for IFR conditions throughout western Washington. Your aircraft is not IFR-equipped.

  • Decision: Don't fly into AIRMET Sierra without IFR capability. Either delay until conditions improve or reroute.


Scenario 2: IFR flight with SIGMET for severe icing

  • You planned an IFR flight from KMSP to KORD. A SIGMET is in effect for severe icing between FL180 and FL240 along your route. You typically cruise at FL200.

  • Decision: Severe icing exceeds even FIKI aircraft capability. Either delay, fly below FL180 (different filed altitude), or reroute around the icing area.


Scenario 3: Cross-country with Convective SIGMET

  • You're en route from KDFW to KIAH. A Convective SIGMET is issued for a line of thunderstorms moving across central Texas, valid for 2 hours.

  • Decision: Don't penetrate the line. Either deviate significantly south to avoid the affected area, divert and wait for the line to pass (typically 1-3 hours), or land at an intermediate airport before reaching the affected zone.


On the Written Test and Checkride

AIRMETs and SIGMETs appear consistently on tests and oral exams. The most commonly tested topics:

  • Difference between AIRMET and SIGMET

  • The three AIRMET types (Sierra, Tango, Zulu)

  • AIRMET Sierra criteria (ceiling below 1,000, visibility below 3 SM)

  • AIRMET Tango criteria (moderate turbulence, sustained winds 30+ knots)

  • AIRMET Zulu criteria (moderate icing)

  • SIGMET criteria (severe icing, severe turbulence, dust/sand, volcanic ash)

  • Convective SIGMET criteria (severe thunderstorms, hail 3/4", tornadoes)

  • Validity periods (AIRMET 6h, SIGMET 4h, Convective SIGMET 2h)


SIGMET criteria:

  • Severe icing

  • Severe/extreme turbulence (non-convective)

  • Dust/sandstorm < 3 SM visibility

  • Volcanic ash

  • Tropical cyclone (winds 64+ kt)


Convective SIGMET criteria:

  • Severe thunderstorms (winds ≥ 50 kt)

  • Hail ≥ 3/4 inch

  • Tornadoes

  • Embedded thunderstorms

  • Lines of thunderstorms

  • Wide areas of thunderstorms


Where to access:

  • 1800wxbrief.com

  • aviationweather.gov

  • EFB apps

  • Flight Watch (122.0)

  • HIWAS broadcasts

  • ATC (in flight)


Key validity:

  • AIRMETs — 6 hours

  • SIGMETs — 4 hours (6 for tropical/volcanic)

  • Convective SIGMETs — 2 hours

  • CWAs — typically 2 hours



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Author: Nathan Hodell

CFI, CFII, MEI, ATP, Creator and CEO

Nathan is an aviation enthusiast with thousands of hours of flying and dual instruction over the past 15+ years. Through his aviation career he has been able to earn his ATP, fly as an airline pilot, own/operate flight schools, and create and host wifiCFI.



 
 
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