Aviation Weather
Before you ever touch the controls of an aircraft, you will be reading weather reports. Not because someone forces you to, but because flying without understanding the current weather is not something any responsible pilot would consider. The METAR is the primary tool for that understanding, and yet most student pilots encounter it for the first time and find it looks like a coded message from another era.
It is, in a sense. METAR is an ICAO standard used by aviation authorities, air traffic control, dispatchers, and pilots around the world. Once you know the structure, a METAR becomes one of the most information-dense, precise documents you will ever read. In under two lines of text, it tells you almost everything you need to know about the weather at a specific airport at a specific moment.
This guide walks through every field of a real METAR, decoded clearly, so you can read one with confidence before your first flight lesson.
Paste any report into our free Live METAR Decoder and see every field explained in plain English instantly.
METAR stands for Meteorological Aerodrome Report (the acronym derives from the original French: Meteorologique d'Aeroport). It is an observation of actual weather conditions at an airport or aerodrome, recorded at a standardised time, typically at the top of every hour (routine METAR) or when conditions change significantly (a SPECI, or special observation).
The METAR tells you what is happening right now at the reporting station: wind direction and speed, visibility, present weather, cloud layers and heights, temperature and dewpoint, and atmospheric pressure. Every one of those elements has a direct bearing on whether a flight is safe, legal, or even possible under the applicable flying rules.
A VFR (Visual Flight Rules) pilot needs to know whether the ceiling and visibility meet the minimums for their flight. An IFR (Instrument Flight Rules) pilot uses the METAR to assess approach conditions. Both need the wind and pressure information for takeoff, landing, and altimeter setting. The METAR is not background reading. It is an operational document that informs real decisions before every flight.
The best way to learn a METAR is to work through a real one, field by field. Here is the example we will decode throughout this guide:
Every METAR begins with the ICAO location indicator for the reporting aerodrome. These four-letter codes are standardised globally. The first letter (or first two letters) identifies the region or country: E for northern Europe, K for the continental United States, Y for Australia, O for the Middle East, and so on.
If you see a METAR starting with K, you are reading an FAA-format report from the US, which has some differences from ICAO format: visibility in statute miles, altimeter in inches of mercury, and cloud heights that may be abbreviated. The core structure is the same, but knowing which system applies helps you read correctly.
The time group in a METAR is always Coordinated Universal Time, also called UTC or Zulu time. The format is a six-digit number: two digits for the day of the month, followed by four digits for hours and minutes in UTC, followed by the letter Z.
So 301250Z means the 30th day of the month at 12:50 UTC. If you are flying in Sydney (UTC+10 in summer) and the METAR says 0300Z, the local time at the airport is 1:00 PM. Converting UTC to local time is a basic skill you need as a pilot, and you will do it so often it becomes automatic.
Routine METARs are issued every hour, on the hour (the :50 in our example is common for some stations that issue slightly before the hour). Special observations, called SPECIs, are issued any time conditions change significantly, such as a sudden drop in visibility or wind shift.
Wind in a METAR is reported as a five or six character group. The first three digits are the direction the wind is blowing FROM, in degrees true. The next two (or three) digits are the speed. The suffix tells you the unit: KT for knots, MPS for metres per second, KMH for kilometres per hour (rare).
Common variations include:
Wind direction matters enormously for runway selection and crosswind calculation. A crosswind component beyond the demonstrated crosswind limit of your aircraft, or your own personal limit as a student, is a reason to delay a flight or choose a different runway.
In ICAO-format METARs (used throughout Europe, Asia, Australia, and most of the world), visibility is reported in metres. The value 9999 means 10 kilometres or more. Values below 9999 are specific distances: 4000 means 4,000 metres, 0800 means 800 metres.
In FAA-format METARs (the United States), visibility is in statute miles. A value of 10SM means 10 statute miles or more. Fractions are used for low visibility: 1/4SM is one-quarter statute mile.
Prevailing visibility is the greatest distance at which objects can be seen around more than half the horizon. If visibility varies significantly in different directions, you may see a directional modifier such as 4000NW (4,000 metres toward the northwest).
VFR flight requires specific minimum visibility depending on the airspace class and altitude. Knowing the visibility in a METAR lets you assess immediately whether VFR conditions exist at the destination.
Between the visibility and cloud fields, a METAR may include one or more present weather codes if precipitation or obscuration is occurring. These follow a standardised coding system:
Intensity modifiers precede the code: a minus sign (-) means light, no sign means moderate, and a plus sign (+) means heavy. So -RA is light rain, RA is moderate rain, and +RA is heavy rain. TSRA means thunderstorm with rain, which is a serious condition for any VFR flight.
In our example METAR, there is no present weather group, which means no precipitation or obscuration was occurring at the time of observation.
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Cloud layers are reported using four coverage descriptors, each representing a range of sky cover measured in oktas (eighths of the sky):
The number following the descriptor is the height of the cloud base in hundreds of feet above the aerodrome elevation. FEW025 means a few clouds at 2,500 feet. BKN008 means a broken layer at 800 feet, which in most jurisdictions would place you below VFR minimums and likely into IMC.
The ceiling is defined as the height of the lowest layer reported as BKN or OVC. FEW and SCT layers do not constitute a ceiling. In our example METAR, the lowest layer is FEW025 and the next is SCT040, so there is no ceiling and conditions are VFR.
Up to three cloud layers are reported in a standard METAR. If there are additional layers above, they may not all appear. The abbreviation SKC (Sky Clear) or NSC (No Significant Cloud, meaning no cloud below 5,000 feet and no CB or TCU) may appear when no clouds are present.
Special cloud types that always appear in a METAR when present include CB (Cumulonimbus) and TCU (Towering Cumulus). Even a FEW level CB, such as FEW025CB, is a serious weather indicator. Cumulonimbus clouds contain severe turbulence, icing, and lightning. No VFR pilot should knowingly fly into or near a CB.
Temperature and dewpoint are reported in degrees Celsius, separated by a forward slash. Temperatures below zero are preceded by M (for minus): M05/M10 means minus 5 Celsius with a dewpoint of minus 10 Celsius.
The dewpoint is the temperature to which air must be cooled (at constant pressure) for saturation to occur and condensation to begin. The difference between temperature and dewpoint, the spread, is one of the most useful quick calculations a pilot makes from a METAR.
A spread of 2 to 3 degrees Celsius or less is a warning that fog or low cloud may form, particularly in the evening or early morning as temperatures drop. A large spread indicates drier air and less likelihood of fog. In our example, 14/09 gives a spread of 5 degrees, which is moderate but not immediately concerning.
Temperature also matters for density altitude calculations. High temperatures reduce air density, which degrades aircraft performance. A surface temperature of 35 Celsius at a high-elevation airport can produce density altitudes well above the published field elevation, with meaningful effects on takeoff roll and climb performance.
The altimeter setting in a METAR tells you what pressure to set in your altimeter so that it reads altitude above mean sea level (MSL) at the surface of the aerodrome.
In ICAO-format METARs, the altimeter setting is prefixed with Q and given in hectopascals (hPa), which are numerically identical to millibars. Q1018 means set 1018 hPa in your subscale. In FAA-format METARs, the prefix is A and the value is in inches of mercury to two decimal places: A2992 means 29.92 inHg.
If you set the wrong altimeter value, your altitude readout will be incorrect. At low altitudes, this can have safety implications. As a rule of thumb in the ICAO system, each 1 hPa difference in altimeter setting corresponds to approximately 27 to 30 feet of altimeter error. A QNH that is 10 hPa lower than what you have set means you are actually 270 to 300 feet lower than your altimeter indicates. This matters most near the ground and in mountainous terrain.
Some METARs include a short-term weather trend appended after the main observation. This is called a trend forecast, valid for the two hours following the observation time.
The trend forecast is not a full TAF. It is a short addendum and should be treated as a broad indication rather than a precise prediction. For planning purposes, the Terminal Aerodrome Forecast (TAF) gives more detailed weather expectations over a longer period.
Students sometimes confuse METARs and TAFs, or assume they serve the same purpose. They do not.
A METAR is an observation. It reports actual measured conditions at the time of issue. It looks backward in the sense that it tells you what the weather was like at that specific moment.
A TAF (Terminal Aerodrome Forecast) is a forecast. It predicts expected conditions at an airport over a future period, typically 24 or 30 hours. TAFs use similar coding to METARs but include time-bracketed groups that describe changing conditions throughout the forecast period.
For a complete pre-flight weather picture, you need both: the METAR to understand current conditions and the TAF (or area forecast) to understand what conditions are expected during your planned flight time and at your destination. Using one without the other gives an incomplete picture.
Knowing the fields is only part of reading a METAR correctly. These are the errors that show up most often among students encountering METARs for the first time:
Confusing cloud heights with altitude above sea level. Cloud heights in a METAR are above the aerodrome elevation, not above sea level. At an airport sitting at 2,000 feet MSL, a cloud layer reported at BKN030 is 3,000 feet above the field, meaning the cloud base is at 5,000 feet MSL. Mixing these up leads to incorrect assessments of ceiling and terrain clearance.
Ignoring the dewpoint spread. A METAR can show good visibility and clear skies at 1800 and still produce fog by 2200 if the temperature-dewpoint spread is narrow. The spread is a forward-looking indicator, and students who only read the current visibility can miss a developing fog risk.
Misreading wind direction. Wind direction in a METAR is where the wind is coming FROM, not where it is going. A wind of 270 degrees is blowing from the west toward the east. This is the opposite convention from how we often describe movement. On a westerly runway, a 270-degree wind is a headwind; on an easterly runway, it is a tailwind.
Assuming FEW and SCT layers mean VFR. FEW and SCT layers do not constitute a ceiling, but they can still affect VFR flight. Flying below a SCT layer at 1,500 feet in a busy TMA is a very different situation from the same layer at 8,000 feet over open terrain. The legal minimum and the practical situation are separate considerations.
Using an outdated METAR. A METAR is valid only for the period until the next one is issued, typically one hour. Weather changes. A METAR from 50 minutes ago at a location with active convection may bear little resemblance to current conditions. Check the most recent issue, and cross-reference with SPECIs if conditions are changing.
Not knowing the units. FAA-format METARs use statute miles and inches of mercury; ICAO-format METARs use metres and hectopascals. Flying internationally or using weather services from different countries without knowing which format applies can lead to significant misinterpretation of both visibility and altimeter setting.
SkyPrep's online pilot ground school covers aviation weather in depth, including METARs, TAFs, pressure systems, density altitude, and hazardous weather. Understanding weather before your first lesson means you arrive able to have real conversations with your instructor, not spending expensive flight hours learning what you could have studied on the ground.
Start Ground School for $79 Try a free lesson firstThe first time you read a METAR, it looks like a random string of characters. After reading ten, the structure becomes obvious. After reading a hundred, you extract the key numbers in seconds without consciously thinking about the format.
The goal at the student stage is not to memorise every possible weather code. It is to understand the structure well enough that you know where to look for each piece of information and what it means in operational terms. Wind and QNH go in the aircraft before every flight. Ceiling and visibility tell you whether the flight is legally and practically possible. Temperature and dewpoint give you a fog and icing picture. NOSIG or TEMPO tells you whether conditions are expected to hold.
Work through METARs from your local airport or airports you plan to fly to. Read them daily, even when you are not flying. The pattern becomes automatic, and when conditions are complex, that automatic familiarity lets you spend your mental energy on the analysis rather than the decoding.
Amir Khalifa, the instructor behind SkyPrep, covers aviation weather as a structured module in the ground school course, specifically because weather interpretation is one of the areas where student pilots most benefit from a clear, logical framework before their first flight lesson. Students who arrive at the airfield already able to read a METAR have more productive early lessons and ask better questions from day one.