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VOLMET, SIGMET, AIRMET

Three acronyms that look like brothers but are cousins. VOLMET broadcasts, SIGMET warns, AIRMET specializes for VFR. Knowing how to distinguish them is understanding where to look for the right information.

5 min read
ICAO Annex 3 · ICAO Doc 7488
Stefano Dias, ATCO

VOLMET — The radio weather broadcast

VOLMET (from French vol + météo — flight weather) is a continuous radio broadcast of METAR and sometimes TAF for groups of airports. It's accessible from any aircraft equipped with HF or VHF radio, in flight or on ground.

There are two types of VOLMET:

  • HF VOLMET (high frequencies) — for long-range flights over oceans; broadcasts groups of continental airports (e.g. Shannon VOLMET for Europe)
  • VHF VOLMET (normal aeronautical frequencies) — for regional flights; broadcasts airports near the receiver
Typical VOLMET
"Zurich VOLMET. METAR Zurich 271050Z. Two seven zero degrees, eight knots. Visibility one zero kilometres. Few clouds at four thousand feet. One six, one zero. QNH one zero one eight."

VOLMET is valuable when flying in areas where mobile signal isn't available (high altitude, isolated valleys) or when you want a quick weather update without calling a controller.

VOLMET in Switzerland

Skyguide doesn't have a dedicated Swiss VOLMET, but European VOLMET frequencies cover Switzerland:

  • Zurich VOLMET — no longer in service (ceased years ago)
  • Vienna VOLMET HF — covers central Europe
  • Shannon VOLMET HF — covers western Europe

For local VFR, METAR via app/EFB is more practical today. But for radio emergencies, knowing HF VOLMET is still useful.

SIGMET — Significant Meteorological Information

SIGMET is an alert message issued when severe meteorological phenomena occur (or are forecast) that may compromise flight safety. It's valid for an entire FIR and is mandatory for ATC to distribute to all affected flights.

Phenomena triggering a SIGMET:

  • Isolated thunderstorms or thunderstorm lines (TS)
  • Severe turbulence (SEV TURB)
  • Severe icing (SEV ICE)
  • Severe mountain waves (MTW)
  • Sand/dust storms (SS, DS)
  • Widespread cumulonimbus (CB)
  • Volcanic ash (VA)
  • Tropical cyclones (TC)
Typical SIGMET
*WSSS SIGMET 1 VALID 271500/271900 LSZH-
SWITZERLAND FIR EMBD TS FCST WI N4730 E0700 - N4700 E0830 -
N4630 E0900 - N4700 E0700 TOP FL370 STNR INTSF=*
Decoding: SIGMET issued for Swiss FIR, valid from 15:00 to 19:00 UTC of 27, embedded thunderstorms forecast in area defined by geographic points, top at FL370, stationary and intensifying.
SIGMET = serious danger

When you hear a SIGMET announced in an area you'll cross, don't underestimate. SIGMETs aren't issued for "normal" phenomena — they're reserved for situations that can cause serious incidents. Consider deviation, holding, or flight cancellation.

AIRMET — Aviation Routine Information

AIRMET is similar to SIGMET but for less severe phenomena, specific for low-altitude flight (below FL100 in Europe, FL150 in some areas). It's primarily intended for VFR and visual flight.

Phenomena triggering an AIRMET:

  • Reduced visibility (< 5 km) over extensive area
  • Clouds below 1000 ft AGL (BKN or OVC)
  • Surface wind > 30 kt
  • Moderate turbulence (MOD TURB)
  • Moderate icing (MOD ICE)
  • Moderate mountain waves
Typical AIRMET
*WSSS AIRMET 2 VALID 271500/271900 LSZH-
SWITZERLAND FIR MOD MTW FCST WI ALPS BLW FL100 STNR NC=*
Decoding: AIRMET valid from 15 to 19 UTC, moderate mountain waves forecast in Alpine region, below FL100, stationary and no change.
When you encounter an AIRMET

For Swiss Alpine VFR, AIRMETs on mountain waves and moderate turbulence are frequent in winter. Take them seriously: even though not "severe MTW", they can still make flight very difficult for a beginner VFR.

SIGMET vs AIRMET vs ATIS

ATIS AIRMET SIGMET
Purpose Terminal info (field) Moderate VFR alert Severe alert
Area Airport FIR FIR
Severity Operational Moderate Severe
Example "QNH 1018" "MOD TURB" "SEV TS"
Update Every 30 min At event At event

How to access SIGMET and AIRMET

SIGMETs and AIRMETs are distributed via:

  • AFTN (textual aeronautical network, accessible to ACC and professional operators)
  • EFB apps (SkyDemon, Foreflight, Air Navigation Pro show them on map)
  • Official pre-flight briefing (AIS Switzerland)
  • ATC radio notifications (ATC will warn you if you enter a zone with active SIGMET)
  • MeteoSwiss aviation site

Swiss specifics

🇨🇭 Swiss context

The Swiss FIR (LSZH) issues SIGMETs and AIRMETs relatively frequently for:

- Mountain waves Alpine (autumn-winter) - Summer thunderstorms in pre-Alps - Föhn and strong winds in particular zones (Valais, Engadine)

MeteoSwiss aviation publishes active SIGMETs on its dedicated page. Always check before flight: a SIGMET going into effect while you're in flight will still be communicated by Skyguide via FIS, but better to know it beforehand.

Summary — to remember

  1. VOLMET = radio broadcast of METAR for groups of fields.
  2. SIGMET = alert for severe weather phenomena (severe TS, turbulence, icing).
  3. AIRMET = moderate alert, specific for VFR below FL100.
  4. SIGMET/AIRMET validity = one FIR, several hours.
  5. Always check before flight (MeteoSwiss aviation, EFB).
  6. If you enter active zone, FIS will alert you — but better to know beforehand.

Sources

  • ICAO Annex 3 — Meteorological Service
  • ICAO Doc 7488 — Manual of the ICAO Standard Atmosphere
  • WMO Manual on Codes
  • MeteoSwiss aviation
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