METAR

Key takeaways

METAR belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect METAR to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of METAR from memory before moving on to harder problems.

Reference excerpt

METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting. Raw METAR is highly standardized through the International Civil Aviation Organization (ICAO), which enables it to be understood throughout most of the world.

Report names Although it is capitalized like an acronym, the origin of the word "METAR" has not been confirmed. The United Nations International Civil Aviation Organization (ICAO) refers to the Meteorological Aerodrome Report while other sources link the acronym to METeorological Terminal Aviation Routine Weather Report. Some unofficial English-language sources suggest that the acronym comes from French phrases such as ''MÉTéorologique Aviation Régulière''. However, this seems unlikely since authoritative sources in French agree that the name comes from the ICAO's "METeorological Aerodrome Report". Other organizations make no attempt to connect their terminology with the METAR acronym. For example, in its publication the Aeronautical Information Manual (AIM), the United States Federal Aviation Administration (FAA) describes the report as aviation routine weather report, while the international authority for the code form, the World Meteorological Organization (WMO), describes it as the aerodrome routine meteorological report. The National Oceanic and Atmospheric Administration (part of the United States Department of Commerce) and the United Kingdom's Met Office both employ the definition used by the FAA.

Frequencies and types

METARs typically come from airports or other permanent weather observation stations. Reports are generated once an hour or half-hour at most stations, but if conditions change significantly at a staffed location, a report known as a special (SPECI) may be issued. Some stations make regular reports more frequently, such as Pierce County Airport (ICAO code: KPLU) which issues reports three times per hour. In addition to METARs and SPECIs, ASOS One-Minute Observations (OMO) are updated once a minute. OMOs can be in various formats, including the METAR format. Some METARs are encoded by automated airport weather stations located at airports, military bases, and other sites. Some locations still use augmented observations, which are recorded by digital sensors, encoded via software, and then reviewed by certified weather observers or forecasters prior to being transmitted. Observations may also be taken by trained observers or forecasters who manually observe and encode their observations prior to transmission. In the United States, prior to mid-1990s, most observations were made manually, but today the vast majority are automated or augmented observations.

History The METAR format was introduced internationally on 1 January 1968, and has been modified a number of times since. North American countries continued to use a Surface Aviation Observation (SAO) for current weather conditions until 1 June 1996, when this report was replaced with an approved variant of the METAR agreed upon in a 1989 Geneva agreement. The WMO's publication No. 782 "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the WMO member countries.

Digital dissemination METAR and TAF data are distributed globally through aeronautical fixed telecommunication networks and are also made available via internet services. They are consumed by airline operations centres, automated briefing systems and a wide range of general aviation tools, including web-based briefing portals, electronic flight bags and mobile applications that display weather overlays on maps and provide route-based summaries of observed and forecast conditions.

Information contained in a METAR A typical METAR contains data for the airport identifier, time of observation, wind direction and speed, visibility, current weather phenomena such as precipitation, cloud cover and heights, temperature, dew point, and barometric pressure. This information forms the body of the report, consisting a maximum of 11 groups of information. A METAR may also contain information on precipitation amounts, lightning, and other information that would be of interest to pilots or meteorologists such as a pilot report or PIREP, colour states and runway visual range (RVR). These may be provided in coded or plain language and appended to the end of the METAR as remarks. In addition, a short period forecast called a TREND may be added at the end of the METAR covering likely changes in weather conditions in the two hours following the observation. These are in the same format as a terminal aerodrome forecast (TAF). The complement to METARs, reporting forecast weather rather than current weather, are TAFs. METARs and TAFs are used in VOLMET broadcasts.

Cloud reporting Cloud coverage is reported by the number of "oktas" (eighths) of the sky that is occupied by cloud. Automated substation substitutes time averaging of sensor data gathered during 30-minute period prior to reporting. This is reported as:

The following codes identify the cloud types used in the 8/nnn part of RMK.

Wind reporting Wind observation measures the horizontal vector component of the wind, which includes both direction and speed. These are determined by evaluating the measurement over a 2-minute period. The wind direction is coded with the first three digits in tens of degrees relative to the true north. If wind speed is less than or equal to 6 kn (11 km/h; 6.9 mph), the wind direction will be displayed as variable or "VRB". If the wind speed is greater than 6 knots, but the direction varies more than 60° in the past 2 minutes, METAR will report the range of wind direction. For example, 21010KT 180V240 suggests the wind was variable from 180° to 240° at 10 knots. Immediately after the wind direction is the wind speed, coded in two or three digits measured in knots, km/h or m/s. If during past 10 minutes, the weather station detects more than 10 kn (19 km/h; 12 mph) between minimum and maximum windspeed, METAR determines a wind gust exists and reports the maximum instantaneous windspeed. If the air is motionless, the wind will be reported as calm and coded as 00000KT.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with METAR

Start with the simplest possible case. Write down what METAR claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to METAR before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about METAR ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of METAR

In research: METAR appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses METAR in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: METAR is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1968 introductions, Aviation meteorology, Aviation publications, so understanding it makes those chapters shorter.
In everyday life: Look for METAR outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study METAR in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what METAR means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain METAR out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is METAR in simple terms?

METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting.

Why does METAR matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study METAR?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on METAR.