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Guide for student pilots

How to read a METAR and TAF

A METAR tells you what the weather is at an airport now. A TAF tells you what it is expected to do. Both are written in a compact code that looks harder than it is. This guide decodes one of each, then shows how to use them to decide whether to fly.

Written for training. Formats follow the international (ICAO) standard used in Europe and by aviationweather.gov. National practice varies, so check the details against your own authority’s publications and your school’s manual.

1. A METAR, group by group

This report is invented for the guide. It is not a real observation.

METAR LRBV 221050Z 28008KT 240V310 9999 -SHRA SCT040 BKN070 14/07 Q1018 NOSIG=

  1. METAR LRBV. The type of report and the four-letter ICAO code of the airport.
  2. 221050Z. The observation was made on the 22nd at 10:50 UTC. The Z means UTC, which is not local time.
  3. 28008KT. Wind from 280 degrees at 8 knots. After the speed, G adds a gust (28008G18KT is 8 knots gusting 18), and VRB replaces the direction when it keeps changing. 240V310 says the direction varied between 240 and 310 degrees.
  4. 9999. Visibility in metres. 9999 means 10 kilometres or more. 4000 is 4 kilometres. In the United States visibility is in statute miles instead, for example 10SM.
  5. -SHRA. Present weather. The minus sign means light, a plus sign means heavy, and no sign means moderate. SH is showers and RA is rain, so this is light rain showers. Other codes you will meet: TS thunderstorm, FG fog, BR mist, HZ haze, DZ drizzle, SN snow, FZ freezing, GR hail.
  6. SCT040 BKN070. Cloud layers: amount, then height above the airport in hundreds of feet. SCT040 is scattered cloud at 4,000 ft and BKN070 is broken cloud at 7,000 ft. The amounts are FEW (1 to 2 eighths of the sky), SCT (3 to 4), BKN (5 to 7) and OVC (8). NSC means no significant cloud. CB or TCU after the height (BKN030CB) means cumulonimbus or towering cumulus.
  7. 14/07. Temperature 14 °C and dew point 7 °C. An M in front means below zero: M02 is −2 °C.
  8. Q1018. The QNH, the altimeter setting, is 1018 hectopascals. A report that gives A2992 uses inches of mercury instead, which is the US way.
  9. NOSIG. No significant change expected in the next two hours. Other trends are BECMG (becoming) and TEMPO (temporarily), followed by the expected change.

Put together: wind from the west at 8 knots, good visibility, a light rain shower in the area, scattered cloud at 4,000 ft with a broken layer at 7,000 ft, QNH 1018, and no change expected.

2. Words and groups worth knowing

  • CAVOK replaces visibility, weather and cloud when visibility is 10 kilometres or more, there is no cloud below 5,000 ft (or below the highest minimum sector altitude, if that is higher), no cumulonimbus or towering cumulus, and no significant weather.
  • Ceiling is the height of the lowest broken or overcast layer. Few and scattered clouds do not make a ceiling.
  • Temperature and dew point close together (within about 3 °C) means the air is near saturation, so fog or low cloud may form, especially in the evening and early morning.
  • SPECI is a special report issued between the routine ones because the weather changed significantly. AUTO means it was produced by an automatic station with no human observer, and COR means it corrects an earlier report.
  • RMK introduces remarks, which differ from country to country.

3. A TAF, and how it changes

Again an invented example:

TAF LRBV 220500Z 2206/2306 28008KT 9999 SCT040 BECMG 2212/2214 30015G25KT TEMPO 2214/2218 4000 TSRA BKN030CB PROB30 2300/2304 3000 BR

  1. 220500Z. The forecast was issued on the 22nd at 05:00 UTC.
  2. 2206/2306. It is valid from 06:00 UTC on the 22nd to 06:00 UTC on the 23rd. Every later time is written the same way, day then hour.
  3. 28008KT 9999 SCT040. The starting conditions, in the same code as a METAR: wind, visibility, cloud.
  4. BECMG 2212/2214 30015G25KT. Becoming, between 12:00 and 14:00 UTC, wind from 300 degrees at 15 knots gusting 25. The change is gradual and what follows stays in force afterwards.
  5. TEMPO 2214/2218 4000 TSRA BKN030CB. Temporarily, between 14:00 and 18:00 UTC, visibility 4,000 metres in thunderstorm and rain with broken cumulonimbus at 3,000 ft. These spells are short and cover less than half of the period.
  6. PROB30 2300/2304 3000 BR. A 30 per cent probability of mist with 3,000 metres visibility between 00:00 and 04:00 UTC on the 23rd. PROB40 is the same with 40 per cent.

A group that starts with FM and a time (FM221500) is an abrupt change: from that moment, the conditions that follow replace the earlier ones.

In this example you could expect a pleasant late morning, a gusty west-north-westerly wind in the early afternoon, and possible thunderstorms between 14:00 and 18:00. A flight planned for the afternoon would need a good reason, an escape plan, or a different day.

4. Flight categories

Weather maps and apps, VectorEFB among them, colour each airport by flight category. It is a quick summary of the ceiling and visibility, using the American (FAA) thresholds, which are not an ICAO or European standard:

  • VFR: ceiling above 3,000 ft and visibility above 5 statute miles (about 8 km).
  • MVFR (marginal VFR): ceiling 1,000 to 3,000 ft or visibility 3 to 5 statute miles.
  • IFR: ceiling 500 to below 1,000 ft or visibility 1 to below 3 statute miles.
  • LIFR (low IFR): ceiling below 500 ft or visibility below 1 statute mile.

The categories are a summary, not the law. In Europe the VFR minima come from SERA (SERA.5001 and SERA.5005) and the AIP of the country, in metres and kilometres: for example 5 km flight visibility and 1,500 m horizontally and 300 m vertically from cloud in most airspace between 3,000 ft and 10,000 ft AMSL. They depend on the class of airspace, the height you fly at and your own licence and school rules. Use the category to see the picture quickly, then check your minima.

5. From the reports to a decision

  1. Check the age. Note the time of the METAR and the issue time of the TAF. A report from three hours ago describes another situation.
  2. Cover the whole flight. Read the METAR for where you are now and the TAF for your arrival time and your alternate, from half an hour before to an hour or two after.
  3. Compare with your minima, not with what feels like good weather: cloud base, visibility, wind and crosswind, and your school’s limits for a student on a first navigation flight.
  4. Work out the crosswind. The wind in a METAR is given relative to true north, but the wind the tower or ATIS gives you is relative to magnetic north, so do not mix the two when you compare it with a runway heading.
  5. Look at the trend and the dew point. A falling temperature spread, a TEMPO for thunderstorms or a BECMG towards lower cloud can close an afternoon that opened well.
  6. Decide the limits before you go. Write down what would make you turn back or divert, and which airport you would divert to.

A missing METAR does not mean good weather. Not every airfield publishes one, so use the nearest ones on both sides of the route, the area forecast and a proper briefing.

Where VectorEFB can help

Open any airport to see its latest METAR and TAF decoded next to the raw text, each with its observation time. METAR stations on the map are coloured by flight category, and the airport page shows the runway headwind and crosswind. If an airport publishes no METAR the app says so, and it says something different when the weather service cannot be reached. Use it to check your own reading, not instead of it. See the pilot page or the student page.

VectorEFB is a training and situational awareness aid. It is not certified for navigation. Do the planning yourself first, and use official charts, the AIP, NOTAMs and a proper weather briefing for real flights.

Next: how to plan a VFR cross-country flight. All guides are listed on the guides page.

For training and situational awareness only. Not certified for navigation. Always use official charts, the AIP, NOTAMs and a proper weather briefing for real flights.