TAF.AERO01 · Reading sequence
A METAR describes observed surface weather at an aerodrome. A SPECI is a special observation issued when specified changes occur. A report is a snapshot, not a promise of conditions when you arrive. Reporting intervals and SPECI criteria vary by country.
- Check report type, station and observation time.
- Read wind, visibility and runway visual range.
- Decode present weather and clouds.
- Read temperature, dew point and pressure.
- Read supplementary groups, remarks and any trend forecast.
METAR EGLL 061250Z 24015G25KT 200V280 6000 -RA BKN012 OVC025 12/10 Q1008 NOSIG=
Decode from left to right. The full interpretation appears in the worked-example section.
02 · Identity, time and status
| Group | Interpretation |
|---|---|
| METAR / SPECI | Routine / special observation |
| EGLL | Four-character station identifier; ICAO differs from three-letter IATA airline codes. Some feeds include national identifiers. |
| 061250Z | Day 06 at 12:50 UTC. Month and year come from context. Z means UTC. |
| AUTO | Fully automated report; sensors do not sample every condition around the airport. |
| COR | Corrected report. Use the corrected version; placement varies nationally. |
| NIL | Report unavailable, not good weather. |
| RMK | Start of remarks, particularly important in US reports. |
| = | End-of-message delimiter, sometimes removed by feeds. |
Observation time is different from download or feed-refresh time. At month boundaries, day 31 followed by day 01 can be consecutive days. Resolve month/year against the report context. A successful feed refresh does not make an old airport observation new.
03 · Wind and its variations
| Group | Interpretation |
|---|---|
| 24015KT | Wind from 240° true at 15 knots |
| 24015G25KT | Mean 15 kt; gusts 25 kt |
| 00000KT | Calm |
| VRB03KT | Variable direction; 3 kt |
| 200V280 | Direction varies clockwise between 200° and 280° |
| 36010KT | From true north; 000 is reserved for the calm group |
| 18005MPS | From 180° at 5 metres/second, about 9.7 kt |
| 18020KMH | Kilometres/hour in legacy/national reports, about 10.8 kt |
| 270P99KT | Speed above the maximum encodable value; P means greater than |
| /////KT | Wind unavailable, not calm |
Wind direction is where wind comes from, referenced to true north. Runway numbers normally reflect magnetic headings. Convert both to the same reference before computing runway components. Spoken ATC/ATIS conventions can differ.
For speed V and wind/runway angle θ: headwind = V × cos θ; crosswind magnitude = V × |sin θ|. Negative headwind is tailwind. Consider gusts and direction variability. A wind-favoured runway is a calculation, not an ATC assignment.
1 kt = 1 nautical mile/hour; 1 m/s ≈ 1.944 kt; 1 km/h ≈ 0.540 kt. Gust and variable-direction reporting thresholds depend on the observing convention.
04 · Visibility and runway visual range
| Group | Interpretation |
|---|---|
| 8000 | Prevailing visibility 8,000 m |
| 9999 | 10,000 m or more, not exactly 9,999 m |
| 0000 | Less than 50 m |
| 4000 1200SW | Prevailing 4,000 m, minimum 1,200 m to the southwest |
| NDV | Directional visibility variation cannot be determined by the automated system |
| 10SM | 10 statute miles, about 16,093 m |
| 1 1/2SM | 1½ statute miles, about 2,414 m |
| M1/4SM | Less than ¼ statute mile, less than about 402 m |
| P6SM | Greater than 6 statute miles, greater than about 9,656 m; common in US TAFs |
| R27R/0600U | Runway 27 Right: RVR 600 m, increasing |
| R09/P2000 | RVR greater than 2,000 m |
| R09/M0050 | RVR less than 50 m |
| R24/0800V1200D | RVR varies 800–1,200 m, decreasing |
| R04L/2400FT | RVR 2,400 feet; FT explicitly changes the unit |
RVR is runway-specific runway visual range, not prevailing visibility. L/C/R identify left/centre/right; U/D/N mean increasing/decreasing/no distinct tendency; V separates varying values. P/M mean above/below an instrument limit. US RVR commonly uses feet.
SM means statute miles, not nautical miles. 1 SM = 1,609.344 m; 1 NM = 1,852 m. TAF.AERO displays decoded visibility in metres while preserving the original code and inequality. Prevailing visibility, RVR and flight visibility are different measurements, not automatically interchangeable in operating minima.
05 · Weather-code dictionary
Read weather groups in three parts: qualifier, descriptor, phenomenon. Only permitted combinations are used; not every code can be combined with every other code.
| Qualifier | Meaning |
|---|---|
| - | Light intensity |
| No sign | Moderate intensity when intensity applies |
| + | Heavy intensity; +FC is the developed funnel-cloud exception |
| VC | In the vicinity rather than at the observing point; distance conventions depend on the reporting system |
| Code | Meaning |
|---|---|
| MI | Shallow |
| PR | Partial |
| BC | Patches |
| DR | Low drifting |
| BL | Blowing |
| SH | Showers |
| TS | Thunderstorm |
| FZ | Freezing |
| DZ | Drizzle |
| RA | Rain |
| SN | Snow |
| SG | Snow grains |
| IC | Ice crystals / diamond dust |
| PL | Ice pellets |
| GR | Hail |
| GS | Small hail and/or snow pellets |
| UP | Unidentified precipitation (automated reports) |
| BR | Mist |
| FG | Fog |
| FU | Smoke |
| VA | Volcanic ash |
| DU | Widespread dust |
| SA | Sand |
| HZ | Haze |
| PY | Spray (national use) |
| PO | Dust/sand whirls |
| SQ | Squalls |
| FC | Funnel cloud; +FC indicates tornado/waterspout |
| SS | Sandstorm |
| DS | Duststorm |
-SHRASN VCTS FZFG
Light showers of rain and snow; thunderstorms in the vicinity; freezing fog. Read each complete group separately.
Common combinations: TSRA thunderstorm with rain; +TSRAGR thunderstorm with heavy rain and hail; FZRA freezing rain; FZDZ freezing drizzle; SHSN snow showers; BLSN blowing snow; DRSN low drifting snow; MIFG shallow fog; BCFG fog patches; PRFG partial fog.
Fog normally corresponds to visibility below 1,000 m. Mist is not simply another word for fog: standard BR reporting uses visibility at least 1,000 m up to the applicable reporting threshold. Patchy or shallow fog can coexist with better prevailing visibility. Thunderstorm coding without RA does not remove the thunderstorm hazard.
06 · Clouds, obscuration and ceiling
| Code | Meaning |
|---|---|
| FEW | 1–2 eighths of sky (oktas) |
| SCT | 3–4 oktas |
| BKN | 5–7 oktas; a ceiling layer |
| OVC | 8 oktas; a ceiling layer |
| VV003 | Sky obscured; vertical visibility 300 ft |
| VV/// | Sky obscured; vertical visibility unavailable |
| SKC | Sky clear (manual/national reporting) |
| CLR | No cloud detected within the automated reporting range; US systems commonly report up to 12,000 ft |
| NSC | No significant cloud under applicable criteria; not necessarily cloudless |
| NCD | No cloud detected by an automated observing system |
| CB / TCU | Cumulonimbus / towering cumulus suffix, e.g. SCT025CB |
| /// | An unavailable element, never zero |
Multiply the three-digit height by 100 to obtain feet above aerodrome level: FEW008 is few at 800 ft; SCT020CB is scattered cumulonimbus at 2,000 ft; BKN045 is broken at 4,500 ft. These are not flight levels or heights above mean sea level.
The ceiling is the lowest BKN/OVC layer, or vertical visibility into an obscuration. FEW and SCT do not define a ceiling. In FEW005 SCT012 BKN030 OVC080, the ceiling is 3,000 ft despite cloud at 500 ft. VV002 reports vertical visibility 200 ft. BKN/// is an unknown base, not an unlimited ceiling.
CB and TCU identify cloud types significant to aviation. An automated clear code does not rule out cloud outside the detection range, or weather hazards outside the sampled area.
07 · CAVOK and unknown values
CAVOK replaces visibility, weather and cloud groups when its criteria are satisfied together: visibility at least 10 km; no operationally significant cloud below 5,000 ft or the highest minimum sector altitude, whichever is higher; no CB/TCU; and no significant weather under the applicable reporting criteria.
Slashes represent unavailable data. A missing observation is unknown, never zero and never an assurance that a phenomenon is absent. A missing visibility group cannot be used as a good-visibility report.
08 · Temperature, dew point and altimeter setting
| Group | Interpretation |
|---|---|
| 18/12 | Temperature +18°C; dew point +12°C |
| M03/M07 | Temperature −3°C; dew point −7°C |
| 00/M00 | Rounded near-zero values; M preserves a negative sign |
| 10/// | Temperature 10°C; dew point unavailable |
| Q1013 | QNH 1,013 hPa |
| A2992 | Altimeter setting 29.92 inHg |
| Q//// | QNH unavailable |
A small temperature/dew-point spread means air near saturation; it does not alone guarantee fog or provide a reliable cloud-base forecast. The pressure group is an altimeter setting, not necessarily the station pressure or the SLP remarks value.
1 inHg ≈ 33.864 hPa. A3000 is about 1,016 hPa. Use the authorised current setting and units for the operation, not a conversion guessed from a different pressure field.
09 · Recent weather, shear and METAR trend
| Code | Meaning |
|---|---|
| RERA / RETS / REFG | Recent rain / thunderstorm / fog; not necessarily occurring now |
| WS RWY24 / WS ALL RWY | Wind shear associated with runway 24 / all runways |
| NOSIG | No significant change forecast in the trend period, normally the next two hours |
| BECMG / TEMPO | Becoming / temporary fluctuations |
| FM1300 / TL1500 / AT1400 | In a trend: from 13:00 / until 15:00 / at 14:00 UTC |
| NSW | No significant weather; used in applicable change/trend contexts to end earlier significant weather |
An appended trend is a forecast, separate from the observed conditions. Not all airports issue trends. METAR trend FM1300 syntax differs from a TAF’s full FMDDHHMM group.
TEMPO FM1300 TL1500 2000 SHRA BKN008
Temporary conditions from 13:00 until 15:00: 2,000 m visibility, rain showers, broken at 800 ft. Read unspecified elements according to the applicable trend rules.
10 · US remarks reference
RMK starts national supplementary information. Automated and augmented reports may contain different groups. The following are common US formats.
| Remark | Meaning |
|---|---|
| AO1 / AO2 | Automated station without / with precipitation discrimination |
| PK WND 28045/1230 | Peak wind 280°/45 kt at 12:30 UTC; minutes-only times also occur |
| WSHFT 1215 FROPA | Wind shift at 12:15 UTC associated with frontal passage |
| TWR VIS / SFC VIS | Tower / surface visibility, in statute miles in US remarks |
| VIS 1/2V2 | Visibility varies ½–2 SM |
| CIG 005V010 | Ceiling varies 500–1,000 ft |
| CIG 002 RWY11 | Ceiling 200 ft at runway 11 sensor |
| RAB05E30 | Rain began at minute 05 and ended at minute 30; B/E mean began/ended |
| TSB20 / TSE45 | Thunderstorm began at minute 20 / ended at minute 45 |
| OCNL / FRQ / CONS | Occasional / frequent / continuous, e.g. lightning frequency |
| LTG IC / CC / CG / CA | Lightning: in-cloud / cloud-to-cloud / cloud-to-ground / cloud-to-air |
| DSNT / VC / OHD / ALQDS | Distant / vicinity / overhead / all quadrants |
| MOV NE | Moving northeast |
| VIRGA | Precipitation evaporating before reaching the surface |
| T00171006 | Precise temperature +1.7°C, dew point −0.6°C; 0/1 sign flags precede three-digit tenths values |
| SLP132 | Sea-level pressure 1,013.2 hPa; restore a leading 9 or 10 to yield a plausible pressure |
| P0007 | Hourly precipitation 0.07 inches; P0000 can represent a trace |
| 60012 / 70045 | 3-/6-hour precipitation 0.12 inches (period depends on time); 24-hour total 0.45 inches |
| 10025 / 21010 | 6-hour maximum +2.5°C / minimum −1.0°C |
| 4snTTTsnTTT | 24-hour maximum and minimum temperatures in tenths °C with sign flags |
| 5appp | 3-hour pressure tendency: a describes tendency shape; ppp gives magnitude in tenths hPa |
| 4/008 | Snow depth 8 inches |
| 933006 | Water equivalent of snow on ground 0.6 inches |
| SNINCR 2/10 | Hourly snow increase 2 inches; total depth 10 inches |
| PRESRR / PRESFR | Pressure rising rapidly / falling rapidly |
| TSNO / FZRANO | Thunderstorm / freezing-rain information unavailable |
| PNO / PWINO / RVRNO | Precipitation amount / present-weather identification / RVR unavailable |
| CHINO / VISNO + location | Cloud-height / visibility sensor unavailable at a secondary location |
| $ | Automated station maintenance indicator |
SLP is not an altimeter-setting substitute. Precise temperatures can explain rounding in the body group. The maintenance indicator does not identify a specific failed measurement. For uncommon remarks, consult the issuing service’s observing manual.
11 · National, military and legacy variations
International reports commonly use metres and Q pressure groups; US reports use SM and A groups. National differences also affect automation, optional remarks, trend availability and weather reporting thresholds. Canadian and military reports include additional local conventions.
Military colour states BLU WHT GRN YLO1 YLO2 AMB RED use military cloud/visibility thresholds. They are not VFR/MVFR/IFR/LIFR. BLACK/BLK indicates an aerodrome/runway usability restriction in the applicable system; consult the relevant military publication for thresholds.
Legacy archives may contain runway-state groups such as R24/421594 or a compact eight-digit form. They encode runway, deposit type, contaminated extent, depth and friction/braking information. They are not RVR. Current runway-condition assessment uses the applicable runway condition report/SNOWTAM framework; a historic friction code is not a current braking-performance guarantee.
Sea-state supplements can include W15/S2 (water temperature 15°C; sea-state code 2) or an H wave-height group. Bulletin headers and rare national additions need the issuing authority’s tables. This guide covers the standard vocabulary and common extensions; it does not treat every historical local code as interchangeable.
12 · Flight categories
| Category | Ceiling AGL | Visibility: US thresholds |
|---|---|---|
| VFR | Above 3,000 ft | Above 5 SM |
| MVFR | 1,000–3,000 ft inclusive | 3–5 SM inclusive |
| IFR | 500 to below 1,000 ft | 1 to below 3 SM |
| LIFR | Below 500 ft | Below 1 SM |
Use the worse of ceiling and visibility. 4,000 ft with 2 SM is IFR; 700 ft with 10 SM is also IFR. 1 SM ≈ 1,609 m; 3 SM ≈ 4,828 m; 5 SM ≈ 8,047 m. These are display categories, not every state’s legal VFR or approach minima. Missing data must not be silently classed as VFR.
13 · Worked reports
METAR EGLL 061250Z 24015G25KT 200V280 6000 -RA BKN012 OVC025 12/10 Q1008 NOSIG=
| Token | Decoded |
|---|---|
| EGLL 061250Z | Heathrow, day 06 at 12:50 UTC |
| 24015G25KT 200V280 | 240° true, 15 kt gust 25; direction varies 200–280° |
| 6000 -RA | 6,000 m visibility, light rain |
| BKN012 OVC025 | Broken 1,200 ft and overcast 2,500 ft; ceiling 1,200 ft |
| 12/10 Q1008 | 12°C, dew point 10°C; QNH 1,008 hPa |
| NOSIG | No significant change in the trend period |
METAR KJFK 061651Z 18012G22KT 1 1/2SM -SN BR OVC008 M02/M03 A2992 RMK AO2 T10221033=
Day 06, 16:51 UTC. Southerly wind 12 kt gusting 22. Visibility about 2,414 m; light snow and mist; ceiling 800 ft. Temperature −2°C, dew point −3°C, altimeter 29.92 inHg. AO2 has precipitation discrimination. Precise values −2.2°C and −3.3°C. Both ceiling and visibility meet the US IFR category.
14 · Practise and check
METAR WSSL 060100Z VRB03KT 9999 SCT018 BKN030 29/25 Q1009=
Reveal the decoding
Seletar, day 06, 01:00 UTC. Variable wind 3 kt. Visibility ≥10 km. Scattered 1,800 ft, broken 3,000 ft; ceiling 3,000 ft. Temperature 29°C, dew point 25°C; QNH 1,009 hPa. MVFR display category because 3,000 ft is within MVFR.
SPECI EGLL 062015Z 00000KT 0800 R27R/0550D FZFG VV002 M01/M01 Q1020=
Reveal the decoding
Special report day 06 at 20:15 UTC. Calm. Visibility 800 m. Runway 27 Right RVR 550 m decreasing. Freezing fog, vertical visibility 200 ft, temperature and dew point −1°C, QNH 1,020 hPa. LIFR display category.
Explain why SCT is not a ceiling, why 9999 is a lower bound, why Q differs from SLP, and why a trend is a forecast before progressing to TAFs.
15 · Archive appendix: runway-state codes
Use this section to read historic reports, not to infer a current runway condition. A legacy group encodes runway designator, deposit, extent, depth and friction/braking information. An example is R24/421594: runway 24, dry snow, 11–25% coverage, depth 15 mm, historical braking code 94. Current operational runway-condition reports use the applicable GRF/RCR/SNOWTAM system.
| Position | Code values |
|---|---|
| Runway | 01–36: runway identifier (left where paired); adding 50 identifies the right runway in the compact legacy convention; 88: all runways; 99: previous information repeated |
| Deposit | 0 clear/dry; 1 damp; 2 wet/water patches; 3 rime/frost; 4 dry snow; 5 wet snow; 6 slush; 7 ice; 8 compacted/rolled snow; 9 frozen ruts/ridges; / unknown |
| Extent | 1: ≤10%; 2: 11–25%; 5: 26–50%; 9: 51–100%; / unknown |
| Depth | 00: less than 1 mm; 01–90: millimetres; 91 unused; 92: 10 cm; 93: 15 cm; 94: 20 cm; 95: 25 cm; 96: 30 cm; 97: 35 cm; 98: ≥40 cm; 99: runway non-operational due to snow/ice/clearance; // not significant or not reported under the applicable convention |
| Friction/braking | 00–90: historical measured coefficient ×100; 91 poor; 92 medium/poor; 93 medium; 94 medium/good; 95 good; 99 unreliable; // not reported |
CLRD indicates previously reported deposits cleared in the legacy convention; SNOCLO indicates closure due to snow. These groups do not supersede current runway closure information or NOTAMs. National archives may differ; identify the code edition before using its numeric fields.
Continue learning
Reference publications: FAA Aviation Weather Handbook and UK Met Office decoding guidance. Examples are original training examples. For rare national groups, use the issuing state’s current meteorological publication.
Reviewed 6 October 2026.