METAR is an observation
METAR is a coded aerodrome meteorological report at a stated UTC time. Its group order is deliberate. Read it from report type through location, time, wind, visibility, weather, cloud, temperature and pressure before looking for supplementary information.
Time and place matter
The ICAO location indicator tells you which aerodrome is observed. The date-time group ends in Z for UTC. A report may be routine or special, but it always needs to be read as a time-stamped observation, not a forecast.
A report can be operationally old even when correctly decoded. Compare its issue time with the planned arrival time and then read the TAF and trend for expected change.
Transmission layout
METAR and SPECI use the same basic code sequence. An equals sign marks the end of a completed message. This helps when messages are transmitted in a bulletin or copied from a display.
Decode the groups in order rather than searching for one desired value such as QNH or cloud base.
Wind, visibility and RVR
The wind group gives direction and mean speed, with gust and variation when reported. Visibility is normally prevailing visibility. RVR is runway-specific and is added when the reporting conditions require it.
Wind group discipline
A direction is given in degrees true in the coded report. Gusts and directional variation change the take-off and landing assessment. A calm or variable report should not be treated as an absence of wind-shear risk elsewhere in the profile.
Compare the observed direction with runway orientation, TAF change groups and any windshear information. The present wind is a point observation, not a guarantee for the landing time.
RVR detail
RVR groups identify a runway and visual range. P and M qualify values outside a reportable range, while a tendency letter shows whether the reported RVR is increasing, decreasing or showing no marked change.
Use RVR with the applicable operating minima and trend. Do not replace it with general visibility because they are different observations.
Weather, cloud, temperature and QNH
The weather group describes present weather at or near the aerodrome. Cloud groups state amount and height above aerodrome level, with CB or TCU identified when significant convective cloud is reported.
Weather-code logic
A code can contain intensity or proximity, a descriptor and a precipitation or obscuration phenomenon. Read the group in that order. It explains why a single code can carry several operational clues.
Vertical visibility is used when the sky is obscured. It is not a cloud-base forecast. It tells the crew that the observer cannot see the sky sufficiently to report the normal cloud layers.
Temperature and pressure
Temperature and dew point help assess moisture and fog risk. QNH is the pressure setting reported in the METAR. The report is not a substitute for checking the latest ATIS or ATC setting before use.
Cloud, temperature and weather must be read together. A low spread with a small temperature-dew point difference and mist has a different trend risk from a high cloud layer in dry air.
CAVOK and supplementary information
CAVOK replaces visibility, RVR, present weather and cloud groups only when all applicable conditions are satisfied. It is a compact statement with strict meaning, not a general statement that the flight is safe.
Supplementary groups
Recent weather begins with RE and reports significant weather that has ceased or reduced. Windshear may be reported for a runway or all runways. Sea-surface, runway state, SNOCLO and remarks provide additional operational detail where included.
Read supplementary groups after the core observation, then decide whether they change the departure, arrival or alternate plan. A recent thunderstorm can still matter even if the present weather group is quiet.
Avoid false shortcuts
Do not infer a cloud base from CAVOK, or assume every omitted group means no hazard. The code rules decide what is shown. Local procedures and the current airport information complete the briefing.
CAVOK conditions,Recent weather RE,Windshear WS,Runway state
SPECI and automatic reports
SPECI is a special aerodrome report issued when significant change occurs between routine observations. It has the same coding structure as a METAR, so the reading method does not change.
Operational change triggers
Wind, visibility or RVR, significant weather, cloud or vertical visibility can pass defined thresholds and require a special report. The exact local reporting criteria matter because a SPECI is intended to alert users to a change that can affect operations.
A SPECI must be compared with the earlier routine report. The difference tells the crew whether the weather has improved, deteriorated or become more variable.
Automatic observations
An automatic report should be recognised as such. Sensors observe particular elements well, but some weather phenomena and cloud observations can have limitations. Use a human observation, radar, ATIS or warning when available to resolve a safety-critical uncertainty.
SPECI,Threshold change,Automatic report,Compare with prior METAR
TREND and full decode
A TREND is a short landing forecast appended to a METAR or SPECI. NOSIG means no significant change expected. BECMG describes a change, while TEMPO describes temporary fluctuations within the trend period.
Work in group order
A complete decode first establishes the observed baseline. Then the TREND is read as a change from that baseline. This prevents a forecast visibility, wind or cloud group being mistaken for the observed value.
For example, a report can show present acceptable visibility but a TEMPO group can still threaten approach planning. The timing and type of change determine its operational weight.
Final check
Confirm report time, runway wind and visibility, weather and cloud, temperature and pressure, any supplementary warning, then the trend. Compare with the TAF because the two products have different purposes and validity.
Observed baseline,NOSIG,BECMG,TEMPO
Worked METAR decode
METAR VIDP 211500Z 33010KT 6000 FEW040 FEW050CB 29/25 Q1004 NOSIG=
- METAR VIDP is a routine report for Delhi using the four-letter ICAO indicator.
- 211500Z means the 21st day at 1500 UTC.
- 33010KT is wind from 330 degrees true at 10 kt.
- 6000 is prevailing visibility of 6000 m.
- FEW040 FEW050CB gives few cloud at 4000 ft and few cumulonimbus at 5000 ft above aerodrome level.
- 29/25 Q1004 NOSIG gives temperature 29 C, dew point 25 C, QNH 1004 hPa and no significant change in the two-hour trend.
RVR includes runway identification and may use P or M qualifiers with U, D or N tendency. CAVOK replaces visibility, RVR, present weather and cloud only when all code conditions apply. SPECI uses the same code as METAR but is issued when a reporting threshold is crossed. AUTO identifies an automatic observation and the equals sign closes the message.
Weather and cloud detail
The present-weather group can contain intensity, a descriptor and a phenomenon. For example, +SHRA is heavy showers of rain; TSRA is thunderstorm with rain. CB and TCU are the cloud types specifically identified in METAR cloud groups. When sky is obscured, VV002 means vertical visibility 200 ft; three slashes show that it cannot be assessed.
A runway state group may report contamination. SNOCLO indicates that the aerodrome is closed because of snow. The group must be read with current runway and braking information, not treated as a substitute for it.