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Aeronautical weather

METAR and TAF

It looks like a string of cryptic code — LSZA 271050Z 22008KT 9999 SCT040 19/10 Q1018 — but in 30 characters there's the airport's present weather. Decoding it is almost a VFR superpower.

8 min read
ICAO Annex 3
Stefano Dias, ATCO

What are METAR and TAF

METAR (from French Météorologique Aviation Régulier) is the meteorological observation bulletin of an airport, issued every 30 minutes or every hour. It describes the present weather at that precise moment.

TAF (Terminal Aerodrome Forecast) is the meteorological forecast bulletin of an airport, issued 4 times a day (every 6 hours) and valid for 24-30 hours. It describes the forecast weather for future hours.

Together, METAR and TAF are the primary tool for VFR pre-flight weather briefing.

METAR vs ATIS

ATIS is a vocal and regional version of METAR (with additional operational info: runway, NOTAMs). METAR is the textual bulletin, codified to ICAO standards, exchanged worldwide. METAR is the source; ATIS is the operational product derived.

METAR anatomy

Lugano METAR example:

LSZA 271050Z 22008KT 9999 SCT040 19/10 Q1018 NOSIG

Block-by-block decoding:

Block Meaning
LSZA ICAO airport code (Lugano)
271050Z Day 27 of month, time 10:50 UTC
22008KT Wind from 220° at 8 knots
9999 Visibility ≥ 10 km
SCT040 Scattered clouds at 4000 ft above ground
19/10 Temperature 19°C, dewpoint 10°C
Q1018 QNH 1018 hPa
NOSIG No significant variation expected in next 2 hours

Cloud cover codes

Code Meaning Octas
SKC Sky clear 0/8
FEW Few clouds 1-2/8
SCT Scattered 3-4/8
BKN Broken 5-7/8
OVC Overcast 8/8
NSC No Significant Cloud < 5000 ft
CAVOK Ceiling and Visibility OK special

CAVOK is a shortcut meaning: visibility ≥ 10 km, no clouds below 5000 ft, no cumulonimbus, no significant weather. It's the "all good" of aeronautical weather.

Weather codes

Significant weather phenomenon codes:

Code Phenomenon
RA Rain
SN Snow
DZ Drizzle
TS Thunderstorm
FG Fog
BR Mist
HZ Haze
SH Showers
GR Hail

They can be combined and modified with prefixes:

  • + (heavy): +RA = heavy rain
  • - (light): -RA = light rain
  • VC (vicinity): VCTS = thunderstorms in vicinity
Complete METAR
LSZH 271050Z 28015G25KT 6000 -RA BKN025 OVC050 16/14 Q1015 BECMG 4000 RA
Decoding: Zurich, day 27 at 10:50 UTC, wind 280° at 15 kt with gusts to 25 kt, visibility 6000 m, light rain, broken clouds 5-7/8 at 2500 ft and overcast 8/8 at 5000 ft, T 16°C, dewpoint 14°C, QNH 1015. Evolution forecast (BECMG): visibility worsening to 4000 m and normal rain.

TAF anatomy

Lugano TAF example:

TAF LSZA 271100Z 2712/2812 22008KT 9999 SCT040 BECMG 2718/2720 26015KT
PROB30 TEMPO 2722/2806 -SHRA BKN030

Decoding:

  • LSZA: airport
  • 271100Z: issued day 27 at 11:00 UTC
  • 2712/2812: validity from day 27 12:00 to day 28 12:00 UTC
  • 22008KT 9999 SCT040: forecast wind and clouds base
  • BECMG 2718/2720 26015KT: gradual change between 18 and 20 UTC of 27, wind shifts to 260° / 15 kt
  • PROB30 TEMPO 2722/2806 -SHRA BKN030: 30% probability of light rain showers with clouds at 3000 ft between 22 UTC of 27 and 06 UTC of 28

Forecast changes in TAF

TAFs include forecast change indicators:

  • BECMG (becoming): gradual change, duration about 2 hours
  • TEMPO (temporary): temporary variations, duration < 1 hour each
  • PROB30 / PROB40 (probability): 30% or 40% probability of a certain event
  • FM (from): rapid change starting at a precise time

How to use a METAR/TAF in practice

For a VFR flight Lugano → Locarno:

  1. METAR Lugano (departure): current weather, decide whether to take off
  2. METAR Locarno (destination): current weather, decide whether to land
  3. TAF Lugano: forecast departure and any return
  4. TAF Locarno: forecast arrival
  5. METAR/TAF of alternates: backup airports (Bellinzona-Magadino, Ambrì)
Frequent error

Planning only on METAR (present) and ignoring TAF (future). If you take off with CAVOK but TAF forecasts SHRA in 2 hours, you're at risk of returning in IMC conditions. Always check the TAF throughout the flight duration.

Where to find METAR and TAF

Official sources:

  • MeteoSwiss aviation (free, aviation.meteoswiss.ch)
  • VOLMET (vocal broadcast for groups of fields)
  • EFB apps (Foreflight, SkyDemon, Air Navigation Pro)
  • AIS Switzerland (official pre-flight briefing)
  • NOAA Aviation Weather Center (free worldwide site)

Swiss specifics

🇨🇭 Swiss context

MeteoSwiss aviation is the official source for Switzerland. Offers:

- METAR and TAF of all Swiss airfields - GAFOR forecast charts (general aviation forecast) divided by mountain zones - SWC charts (significant weather chart) - Airport webcams

Swiss METARs/TAFs follow the ICAO standard without proprietary extensions. The GAFOR chart is particularly useful for Alpine VFR, because it divides the territory into zones (e.g. Ticino, Valais) and gives simple forecasts like "O" (open VFR), "M" (marginal), "X" (closed).

Summary — to remember

  1. METAR = present observation (every 30 min). TAF = future forecast (24-30h).
  2. METAR anatomy: ICAO + DDHHMMZ + wind + visibility + clouds + T/Td + QNH + trends.
  3. CAVOK = excellent VFR, ceiling >5000 ft, vis >10km, no phenomena.
  4. Cloud codes: FEW, SCT, BKN, OVC.
  5. TAF changes: BECMG, TEMPO, PROB, FM.
  6. MeteoSwiss aviation is the official Swiss source, free.

Sources

  • ICAO Annex 3 — Meteorological Service for International Air Navigation
  • WMO Manual on Codes — METAR/TAF specifications
  • MeteoSwiss aviation — official CH source
  • Aero Locarno · Subject 050 (Meteorology)
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