SIGMET and AIRMET

METAR and TAF describe aerodromes. SIGMET describes the route – and only those phenomena capable of affecting the safety of aircraft operations. Ignoring a SIGMET is something fundamentally different from not reading a TAF.

Applicability: European Union (EASA framework); issued by the responsible meteorological watch office for each flight information region
Rulemaking authority: Commission Implementing Regulation (EU) 2017/373, Annex V (Part-MET), MET.OR.250, MET.TR.250, MET.OR.255 and Annex V Appendix 5
Reviewed by NorthTrack on: 2026-09-13

The legal definition

SIGMET – the definition
Information issued by a meteorological watch office concerning the occurrence or expected occurrence of specified en-route weather and other phenomena in the atmosphere that may affect the safety of aircraft operations, and of the development of those phenomena in time and space. (In substance, after Article 2(93) of Regulation (EU) 2017/373.)

Two features are decisive: a SIGMET concerns the route, not an aerodrome, and it is issued only for phenomena that touch safety – not for unpleasant weather.

Validity and issue

Validity, general
Value: no more than 4 hours · Reference: MET.OR.250(c)
Validity for volcanic ash and tropical cyclones
Value: up to 6 hours · Reference: MET.OR.250(c)
Issue in advance, general
Value: no more than 4 hours before the start of validity · Reference: MET.OR.250(d)
Issue for volcanic ash and tropical cyclones
Value: as soon as practicable, no more than 12 hours in advance, updated at least every 6 hours · Reference: MET.OR.250(d)
Cancellation
Value: as soon as the phenomenon no longer occurs or is no longer expected · Reference: MET.OR.250(b)

A SIGMET is therefore always short-lived information. A briefing four hours old cannot contain a SIGMET issued since.

Three types, one phenomenon per message

MET.TR.250 distinguishes three types of SIGMET: for en-route weather phenomena other than volcanic ash and tropical cyclones, for volcanic ash, and for tropical cyclones. What matters for reading one: a SIGMET names only one of the phenomena listed in Appendix 5. Where several occur, several SIGMET are issued. And a SIGMET for thunderstorms or a tropical cyclone contains no additional information on associated turbulence and icing – those are taken to be included.

The abbreviations of a SIGMET

A SIGMET consists almost entirely of abbreviations. This table covers the ones that appear in virtually every message.

SIGMET — Significant meteorological information
Valid for no more than 4 hours (6 for volcanic ash and tropical cyclones).
AIRMET — Airmen’s meteorological information
For the low-level region; valid for no more than 4 hours.
OBS — Observed
Line 11 of the template: the phenomenon has been observed and is continuing.
FCST — Forecast
Line 11 of the template: the phenomenon is expected.
MOV — Movement or expected movement
Line 14: direction and speed, for example MOV NE 20KT.
STNR — Stationary
Line 14, the alternative to MOV.
OBSC — Obscured *
A thunderstorm hidden in other cloud and therefore not identifiable under visual flight rules.
EMBD — Embedded *
A thunderstorm embedded in layer cloud — likewise not visible.
FRQ — Frequent *
Thunderstorms with little separation between them, barely possible to fly around.
SQL — Squall line *
Thunderstorms arranged in a line.
SEV — Severe *
An intensity level in a SIGMET, for example SEV TURB, SEV ICE.
MOD — Moderate *
An intensity level in an AIRMET, for example MOD TURB.
ISOL — Isolated *
An AIRMET phenomenon, for example ISOL TS.
OCNL — Occasional *
An AIRMET phenomenon, for example OCNL CB.
TURB — Turbulence *
A SIGMET / AIRMET phenomenon.
ICE — Icing *
A SIGMET phenomenon; SEV ICE (FZRA) for freezing rain.
MTW — Mountain wave *
A SIGMET phenomenon, as SEV MTW.
INTSF — Intensifying *
Line 15: the expected change in intensity.
WKN — Weakening *
Line 15: the expected change in intensity.
NC — No change *
Line 15: the expected change in intensity.
TOP — Top *
Line 13, for example TOP FL380 — the upper limit of the phenomenon.
WI — Within *
Line 12: the area is described by corner points in latitude and longitude.

* The English expansion of these codes is defined only in ICAO Doc 8400 (PANS-ABC). That document is not freely available, so the expansion has not been verified against the primary text for this edition.

Compound SIGMET entries

The pattern is the same throughout: qualifier, then phenomenon.

OBSC TS = OBSC (Obscured) + TS (Thunderstorm)
An obscured thunderstorm — hidden in other cloud.

EMBD TSGR = EMBD (Embedded) + TS (Thunderstorm) + GR (Hail)
A thunderstorm embedded in layer cloud, with hail.

SEV ICE = SEV (Severe) + ICE (Icing)
Severe icing.

SEV TURB = SEV (Severe) + TURB (Turbulence)
Severe turbulence.

MOD TURB = MOD (Moderate) + TURB (Turbulence)
Moderate turbulence — an AIRMET phenomenon, not a SIGMET one.

TOP FL380 = TOP (Top)
The phenomenon extends up to flight level 380.

Phenomena that can trigger a SIGMET

thunderstorms – obscured (OBSC), embedded (EMBD), frequent (FRQ) or as a squall line (SQL), each with hail (GR) where applicable
severe turbulence (SEV TURB)
severe icing (SEV ICE), separately for freezing rain (SEV ICE (FZRA))
severe mountain wave (SEV MTW)
heavy dust storm (HVY DS) and heavy sandstorm (HVY SS)
volcanic ash cloud (VA CLD), with the eruption details where applicable
radioactive cloud (RDOACT CLD)
tropical cyclone (TC) from a surface wind speed of 34 kt upwards

How a SIGMET is put together

Appendix 5 to the Regulation lays down the order of the lines. For reading one, knowing the first six positions is enough:

1
Content: Location indicator of the FIR/CTA the message refers to · Form: nnnn
2
Content: Identification and sequence number · Form: SIGMET nnn
3
Content: Period of validity in UTC · Form: VALID nnnnnn/nnnnnn
4
Content: Location indicator of the issuing meteorological watch office, with a hyphen · Form: nnnn–
6
Content: Location indicator and name of the FIR/CTA · Form: nnnn nnnnnnnnnn FIR
10
Content: The phenomenon · Form: e.g. EMBD TS
11
Content: Observed or forecast · Form: OBS [AT nnnnZ] or FCST [AT nnnnZ]
12
Content: Location · Form: e.g. WI with corner points in latitude/longitude
13
Content: Level · Form: e.g. TOP FL380
14
Content: Movement · Form: e.g. MOV NE 20KT or STNR
15
Content: Change in intensity · Form: INTSF, WKN or NC

Extract from Annex V Appendix 5 to Regulation (EU) 2017/373. Under MET.TR.250(c) the sequence number consists of three characters: one letter and two digits.

How to read a SIGMET in 10 seconds
Does the area affect me (position 12)? Does the level affect me (position 13)? Is it still valid (position 3)? Is it getting worse (position 15)? Only after that is it worth looking at the detail.

AIRMET – the level below

AIRMET concerns phenomena capable of affecting the safety of flights in the low-level region which were not already included in the area forecast for low-level flights. AIRMET is issued where the competent authority has determined that the density of traffic below flight level 100 – or up to flight level 150 in mountainous areas, or higher where necessary – justifies it (MET.OR.255(a)). Validity is no more than 4 hours.

Typical AIRMET phenomena are moderate turbulence, moderate icing, moderate mountain wave, mountain obscuration, extensive areas of low cloud, isolated or occasional thunderstorms, and surface wind or surface visibility below defined thresholds.

Not the same everywhere
Whether AIRMET is issued, and to what extent, is decided by the competent authority for each flight information region. What is a matter of course in one country's briefing may be handled differently across the border. The arrangements for each country are in that country's Aeronautical Information Publication.

How a SIGMET reaches the briefing

SIGMET reach pilots through the self-briefing service of the responsible aviation weather service, through the flight-preparation facilities of the aeronautical information service, and in flight through the flight information service. In Germany the aviation weather service sits within the Deutscher Wetterdienst; the dissemination of SIGMET messages to VFR traffic is additionally described in the Aeronautical Information Publication AIP VFR under ENR 1-56.

Official sources

European Commission / EASA: Commission Implementing Regulation (EU) 2017/373 (Annex V "Part-MET", Annex VI "Part-AIS") – Consolidated version 02017R0373-20250501. Open source (retrieved 2026-09-13)
DFS Deutsche Flugsicherung GmbH: Aeronautical Information Publication Germany – AIP VFR – Effective 20 AUG 2026. Open source (retrieved 2026-09-13)
DFS Deutsche Flugsicherung GmbH: Aeronautical Information Publication Germany – AIP VFR, GEN 2-1 to GEN 2-7 "Abkürzungen / Abbreviations" (bilingual German/English) – Effective 20 AUG 2026. Open source (retrieved 2026-09-13)
ICAO: Doc 8400 – Procedures for Air Navigation Services: Abbreviations and Codes (PANS-ABC). Named by Regulation (EU) 2017/373 as the reference for the meaning of the weather abbreviations. – —. Open source (retrieved 2026-09-13)
Deutscher Wetterdienst (DWD), the German national meteorological service: The DWD aviation weather service – advice and self-briefing (German site) – continuously updated. Open source (retrieved 2026-09-13)