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Decoding a METAR, element by element

The fixed order of a METAR, how to identify the ceiling correctly, and the elements that change a release decision rather than merely describing the weather.

Weather reports and forecasts18 min read

Video scheduled

The lesson video for this topic is in production on The Flight Dispatch Room.

Written lesson

The lesson

A METAR is an observation, not a forecast. It tells you what was true at the station at one moment. Its value in dispatch is that it is the ground truth against which every forecast you are working from is either confirmed or called into question.

The elements always appear in the same order

  1. Report type: METAR for a routine hourly observation, SPECI for a special observation triggered by a significant change.
  2. Station identifier: the four-letter ICAO location indicator.
  3. Date and time: six digits, two for day of month and four for time, always in Zulu, suffixed Z.
  4. Modifier: AUTO for a fully automated report, COR for a corrected report. Absent otherwise.
  5. Wind: three digits of direction in degrees true, two or three digits of speed, KT. G indicates gusts. VRB indicates variable direction.
  6. Visibility: prevailing visibility in statute miles in United States reports, suffixed SM.
  7. Runway visual range: R followed by runway, slash, then the RVR value in feet. Present only when reported.
  8. Present weather: intensity, descriptor and phenomena, for example -RA, +TSRA, BR, FG.
  9. Sky condition: layer amount and height in hundreds of feet AGL. SKC, CLR, FEW, SCT, BKN, OVC, or VV for vertical visibility.
  10. Temperature and dew point: two digits each in whole degrees Celsius, separated by a slash. M prefixes a negative value.
  11. Altimeter: A followed by four digits, in inches of mercury with the decimal point omitted.
  12. Remarks: everything after RMK.

Identifying the ceiling

The ceiling is the height above ground level of the lowest broken or overcast layer, or the vertical visibility into an obscuration. FEW and SCT layers are not ceilings, no matter how low they are. This single definition accounts for a large share of the weather questions on the exam.

Reading a full example

METAR KDEN 141853Z 27018G28KT 4SM -SN BKN009 OVC020 M04/M07 A2988 RMK AO2

  • Routine observation at Denver, on the 14th at 1853 Zulu.
  • Wind from 270 degrees true at 18 knots, gusting 28 knots.
  • Prevailing visibility 4 statute miles in light snow.
  • Broken at 900 ft AGL, overcast at 2,000 ft AGL. The ceiling is 900 ft, the lowest broken layer.
  • Temperature minus 4 Celsius, dew point minus 7 Celsius.
  • Altimeter 29.88 inches of mercury.
  • Remarks indicate an automated station with a precipitation discriminator.

The elements that change a decision

Wind gust spread against crosswind limits, the temperature and dew point spread as an indicator of fog formation, the ceiling against approach minimums, and the altimeter setting against pressure altitude for performance. Those four are where an observation stops being information and becomes a constraint on the release.

Examination focus

Key exam concepts

  • METAR is an observation; SPECI is a special observation triggered by significant change.
  • Time is always Zulu, formatted as two digits of day plus four digits of time.
  • Sky layer heights are in hundreds of feet AGL.
  • The ceiling is the lowest BKN or OVC layer, or the vertical visibility into an obscuration. FEW and SCT are never ceilings.
  • Temperature and dew point are whole degrees Celsius, with M for negative values.
  • The altimeter is inches of mercury with the decimal omitted, prefixed A.

Method

Worked examples

Find the ceiling and decide whether the 1-2-3 test is met

Given

  • METAR KMCI 201653Z 15012KT 6SM BR SCT008 BKN025 OVC060 18/17 A2996
  • Airport elevation 1,026 ft MSL.
  • The question asks whether the observed conditions meet the 2,000 ft and 3 SM threshold.

Steps

  1. 1Scan the sky condition group: SCT008, BKN025, OVC060.
  2. 2Discard SCT008. A scattered layer is not a ceiling regardless of height.
  3. 3The lowest broken or overcast layer is BKN025, so the ceiling is 2,500 ft AGL.
  4. 4The threshold is 2,000 ft above airport elevation, which is 2,000 ft AGL. 2,500 exceeds it.
  5. 5Visibility is 6 SM, which exceeds 3 SM.

Answer

Both values are above the threshold at the time of this observation. Note this is an observation only. The 121.619 test requires forecasts or reports covering the full window from one hour before to one hour after ETA, so a single METAR cannot settle the question by itself.

Watch out

Common exam traps

  • Treating a low SCT or FEW layer as the ceiling.
  • Reading layer heights as MSL or as thousands of feet.
  • Missing the M prefix and reading M04 as plus 4 Celsius.
  • Forgetting that visibility in United States METARs is statute miles, not nautical miles.
  • Using a single METAR to answer a question that requires a forecast window.

Test yourself

Practice questions

Choose an answer to reveal the discussion. Every option is explained, including why the wrong ones are attractive.

  1. Q01

    In the report FEW005 SCT012 BKN030 OVC080, what is the ceiling?

  2. Q02

    In a METAR, the group 09015G25KT indicates:

  3. Q03

    A METAR reports 21/20 with light and variable wind at sunset. The most operationally significant implication is:

Verify

Official FAA references

  • AC 00-45Aviation Weather Services — METAR and SPECI format.
  • FAA-H-8083-28Aviation Weather Handbook.
  • 14 CFR 121.619Alternate airport for destination: Domestic operations.

Current regulation text is published on eCFR. Always confirm against the current version before relying on any citation.

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