Reference · 95 terms

METAR and TAF glossary

Every code a general aviation pilot meets in an observation, a forecast, or a briefing, defined in one line. Decoding a whole report instead? Paste it into the METAR decoder.

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Flight categories

The four color-coded bands every weather display uses. They are an operational convention published by the Aviation Weather Center, not a definition in the regulations.

VFR Visual Flight Rules: As a category on a weather display: ceiling above 3,000 ft AGL and visibility above 5 SM. Both have to be true. It describes the weather, not your legal authority to fly in it.
MVFR Marginal VFR: Ceiling 1,000 to 3,000 ft AGL and/or visibility 3 to 5 SM. Either one alone puts the field in the category. Legal VFR in most airspace, and the band where most weather-related decisions actually get made.
IFR Instrument Flight Rules: Ceiling below 1,000 ft AGL and/or visibility below 3 SM. As a category it means the field is below basic VFR minimums in controlled airspace, so VFR arrival or departure needs a Special VFR clearance if one is available.
LIFR Low IFR: Ceiling below 500 ft AGL and/or visibility below 1 SM. A sub-category of IFR, and below the standard minimums of most instrument approaches.
Ceiling: The height above ground of the lowest BKN or OVC layer, or the vertical visibility into an obscuration. FEW and SCT layers are never a ceiling, however low they sit, which is why a field can report 200 ft scattered and still be VFR. BKN008 → 800 ft ceiling

Sky cover and ceiling

How much of the sky a layer covers, in eighths, and which layers are allowed to count as a ceiling.

SKC Sky clear: No cloud layers, reported by a human observer.
CLR Clear: An automated station detects no layers at or below 12,000 ft. It says nothing about cloud above that height, because the sensor cannot see it.
FEW Few: A layer covering 1/8 to 2/8 of the sky. Never a ceiling. FEW035 → few at 3,500 ft
SCT Scattered: A layer covering 3/8 to 4/8 of the sky. Never a ceiling, no matter how low. SCT012 → scattered at 1,200 ft
BKN Broken: A layer covering 5/8 to 7/8 of the sky. The lowest BKN layer is a ceiling, and it is usually the number that sets the flight category. BKN025 → 2,500 ft ceiling
OVC Overcast: A layer covering 8/8 of the sky. Always a ceiling. OVC006 → 600 ft ceiling
VV Vertical visibility: The sky is obscured and the observer cannot see a cloud base, so the report gives how far up you can see instead. Counts as a ceiling. VV002 → indefinite ceiling, 200 ft vertical visibility
Summation amount: Sky cover is reported cumulatively: each layer is coded by its own coverage plus everything below it. A layer can never exceed 8/8, which is why you never see two OVC layers.
CAVOK Ceiling and visibility OK: International shorthand: visibility 10 km or more, no cloud below 5,000 ft or below the highest minimum sector altitude, no cumulonimbus or towering cumulus, and no significant weather. Not used in US reports.
NSC / NCD No significant cloud / no cloud detected: International codes. NSC means no operationally significant cloud and no CAVOK; NCD means an automated sensor found nothing. Not used in US reports.

Visibility

Horizontal visibility at the surface, on the runway, and the prefixes that bound it.

SM Statute miles: The unit US surface visibility is reported in. Note that it is statute, not nautical, and that every visibility minimum in Part 91 is written in statute miles too. 3SM
P6SM: More than 6 statute miles. The top of the reportable range for most automated US stations, so it means "at least 6 and probably a lot more", not exactly 6.
M1/4SM: Less than 1/4 statute mile. The bottom of the reportable range.
M (prefix): Less than. Applied to a value that has hit the bottom of what the sensor can resolve. Also used on a temperature to mean below zero. M1/4SM · M06/M08
P (prefix): More than. Applied to a value at the top of the reportable range. P6SM · R06/P6000FT
RVR Runway visual range: Visibility measured along a specific runway, in feet, by transmissometers near the touchdown zone. Where an approach lists an RVR minimum, RVR is controlling and prevailing visibility is not. R06L/2000FT
9999: International visibility group meaning 10 km or more. Metric visibility elsewhere is reported in meters, so 0800 is 800 m.

Weather phenomena

The present-weather group, built in a fixed order: intensity, then descriptor, then precipitation, then obscuration.

- (minus): Light intensity, prefixed to the precipitation code. -RA → light rain
(no prefix): Moderate intensity. Nothing in front of the code is itself the code. RA → moderate rain
+ (plus): Heavy intensity. On a funnel cloud it means something different: +FC is a tornado or waterspout. +SN → heavy snow
VC In the vicinity: The phenomenon is between 5 and 10 SM of the station, not at it. VCTS on your destination METAR is the one to take seriously. VCTS · VCSH
MI Shallow: A layer less than 6 ft deep. Almost always seen as MIFG, shallow fog.
PR Partial: Covering part of the airport. PRFG means fog over a portion of the field.
BC Patches: Patchy. BCFG is patchy fog, which can close a runway threshold and leave the rest clear.
DR Low drifting: Raised by wind to less than 6 ft above the ground. DRSN
BL Blowing: Raised by wind to 6 ft or more above the ground. BLSN can drop visibility to nothing in seconds.
SH Showers: Precipitation from convective cloud, starting and stopping abruptly. Implies a rough ride underneath it. SHRA · SHSN
TS Thunderstorm: Thunder heard or lightning detected at the station within the last 15 minutes. Reported whether or not precipitation is reaching the ground. TSRA
FZ Freezing: Supercooled liquid freezing on contact. FZRA and FZDZ are the two entries in the present-weather group that most reliably end a light-aircraft flight. FZRA · FZFG
RA Rain: Liquid precipitation in drops larger than drizzle.
DZ Drizzle: Very small, closely spaced drops. Often paired with low ceilings and poor visibility rather than heavy water.
SN Snow: Snow. Reduces visibility fast and accumulates on airframes on the ground.
PL Ice pellets: Frozen raindrops. Their presence means a warm layer aloft with freezing rain somewhere above you.
GR Hail: Hail with stones 1/4 inch or larger. Implies a thunderstorm with a strong updraft.
GS Small hail / snow pellets: Hail smaller than 1/4 inch, or graupel. Still a convective signal.
IC Ice crystals: Diamond dust: tiny crystals falling from a clear sky in very cold air.
UP Unknown precipitation: An automated station detects precipitation but cannot classify it. Treat it as a prompt to look at temperature and dewpoint yourself.
BR Mist: Visibility restricted to between 5/8 and 6 SM by water droplets. Below 5/8 it is coded FG instead.
FG Fog: Visibility below 5/8 SM from suspended water droplets. Variants: FZFG (freezing), MIFG (shallow), BCFG (patches), PRFG (partial).
HZ Haze: Dry particles suspended in the air. Worst looking into sun, which makes an afternoon westbound arrival harder than the reported number suggests.
FU Smoke: Visibility restricted by smoke. Can persist for days downwind of a fire and does not burn off like fog.
DU / SA Widespread dust / sand: Dust or sand in suspension, reducing visibility.
VA Volcanic ash: Volcanic ash. Destroys turbine engines and sandblasts windscreens; avoid entirely rather than by distance.
SQ Squall: A sudden wind increase of at least 16 kt to a sustained 22 kt or more, lasting at least one minute.
FC Funnel cloud: A funnel cloud aloft. Coded +FC when it reaches the surface as a tornado or waterspout.
SS / DS Sandstorm / duststorm: Sand or dust raised to a height that severely restricts visibility.

Wind

Direction, speed, gusts, variability, and the shear groups that ride alongside them.

dddffKT: The wind group: three digits of direction in degrees true, then two or three digits of speed in knots. Tower-reported winds are magnetic; the METAR is true, which is a few degrees of difference worth remembering when picking a runway. 24009KT → 240° at 9 kt
G Gust: Peak gust, appended to the wind group. Reported when the peak exceeds the sustained speed by 10 kt or more. 24009G18KT
VRB Variable: Direction is variable, used when speed is 6 kt or less, or when the direction varies by 60° or more and speed is above 6 kt. VRB04KT
00000KT: Calm. Speed below 3 kt.
V (direction group): A separate group giving the two extremes the direction varied between during the observation. Read it before choosing a runway on a marginal crosswind day. 210V280
WS Wind shear: In a TAF, a non-convective low-level wind shear group: the layer height in hundreds of feet, then the wind at that height. Warns of an airspeed change on approach. WS020/25040KT
LLWS Low-level wind shear: Wind shear below 2,000 ft AGL. Reported by pilots, by airport shear alert systems, and forecast in TAFs as a WS group.
PK WND Peak wind: A remark giving the highest instantaneous wind since the last hourly report, with its direction and the time it happened. PK WND 28045/1732
WSHFT Wind shift: A remark timing a wind direction change of 45° or more in under 15 minutes. Often marks a frontal passage; FROPA is appended when the observer agrees. WSHFT 1715 FROPA

Pressure and altimetry

Altimeter settings, the pressure references behind them, and the altitudes they yield.

A#### Altimeter setting, inches of mercury: The altimeter setting in inches of mercury with the decimal removed. Set it and the altimeter reads field elevation on the ground. A2992 → 29.92 inHg
Q#### QNH, hectopascals: The same setting in hectopascals, used almost everywhere outside the US. 1013 hPa is the equivalent of 29.92 inHg. Q1013
SLP Sea level pressure: A remark giving sea level pressure in tenths of a hectopascal, with the leading 9 or 10 dropped. SLP132 is 1013.2 hPa. SLP132
QFE: A setting that makes the altimeter read zero on the airfield. Used at some military and non-US fields; not a US civil practice.
29.92 / standard pressure: The standard datum: 29.92 inHg, 1013.25 hPa, 15 °C at sea level. Set it at or above 18,000 ft MSL in US airspace, and use it to find pressure altitude on the ground.
Pressure altitude: Altitude above the standard datum plane: what the altimeter reads with 29.92 set. The input performance charts are built around.
Density altitude: Pressure altitude corrected for temperature. The altitude the airplane thinks it is at, and the number that governs takeoff roll and climb rate.

Report structure and remarks

The scaffolding of an observation: what kind of report it is, when, and from what.

METAR Aviation routine weather report: The scheduled hourly surface observation, usually issued in the 5 minutes before the hour. An observation of what is happening now, never a forecast.
SPECI Aviation selected special weather report: An unscheduled observation triggered by a significant change: a category-crossing ceiling or visibility, a wind shift, the start or end of thunderstorms or freezing precipitation. A SPECI arriving is itself information.
AUTO: The report came from an automated station with no human augmentation. Automated stations cannot see above about 12,000 ft, cannot identify cloud type, and report UP when they cannot classify precipitation.
COR Corrected: A corrected report, replacing one already transmitted.
NIL: No report available for that station at that time.
Date-time group: Two digits for the day of the month, four for the time, and a Z for Zulu. Always Zulu; a report is never in local time. 031753Z → 3rd at 1753Z
Temperature / dewpoint group: Temperature then dewpoint in whole degrees Celsius, separated by a slash, with M for below zero. A small spread means moisture is close to condensing: fog, or ice in the induction system. 12/09 · M03/M06
RMK Remarks: Everything after RMK is supplementary. US remarks carry the precise numbers the coded body rounds off, plus observer notes on what the weather is doing.
AO1 / AO2: Automated station type. AO1 has no precipitation discriminator and cannot tell rain from snow; AO2 can. It tells you how much to trust the present-weather group.
T group: A remark giving temperature and dewpoint to a tenth of a degree, with 1 as the sign digit for below zero. Worth reading when the coded value sits right on freezing. T01170094 → 11.7 °C / 9.4 °C
$: The station needs maintenance. Some element of the report may be wrong, and there is no indication of which.

TAF change groups

How a forecast says that conditions are about to become something else.

TAF Terminal aerodrome forecast: A forecast for the area within 5 SM of the center of a runway complex, issued four times a day for most sites and valid 24 or 30 hours. It covers the airport, not your route.
Valid period group: Day and hour the forecast starts, then day and hour it ends, in Zulu. A TAF that has expired is not a forecast. 0318/0424
FM From: A rapid and permanent change, complete within an hour of the stated time. Everything before it is replaced: an FM group restates the whole forecast, not just what changed. FM031800
BECMG Becoming: A gradual change expected at some point inside the stated window, usually two hours or less. Only the elements listed change; everything else carries forward. BECMG 0312/0314
TEMPO Temporary: Fluctuating conditions expected to last under an hour at a time, and in total less than half the stated window. Plan for it happening while you are on approach. TEMPO 0315/0318 3SM SHRA
PROB30 / PROB40: A 30% or 40% chance of the conditions that follow. Below 30% the forecaster says nothing; at 50% or more it stops being a probability group and becomes the forecast. PROB30 0320/0322 1SM TSRA
AMD Amended: The forecast has been reissued before its scheduled time because the previous one was wrong. An amendment appearing is a signal in itself.
NSW No significant weather: Used in a change group to say that previously forecast weather has ended.

Advisories and notices

The hazard products that arrive alongside the observations, and who issues them.

AIRMET Airmen's meteorological information: Advisory of weather hazardous to light aircraft: Sierra for IFR and mountain obscuration, Tango for turbulence and strong surface winds, Zulu for icing and freezing level. Issued graphically as G-AIRMETs since the textual product was retired in 2025.
G-AIRMET Graphical AIRMET: The graphical form: snapshots every three hours out to twelve, so you can see the hazard area move rather than reading one smeared bounding box.
SIGMET Significant meteorological information: Advisory of weather hazardous to all aircraft: severe icing, severe or extreme turbulence, widespread dust or sandstorms, and volcanic ash. Valid four hours.
Convective SIGMET: Issued for severe thunderstorms, embedded or line thunderstorms, or an area of thunderstorms with heavy precipitation. Valid two hours, and it implies severe turbulence, icing and low-level wind shear whether or not they are stated.
CWA Center weather advisory: A short-notice advisory issued by a center weather service unit for conditions affecting a single ARTCC area, valid up to two hours. Often the first warning that something is developing.
PIREP Pilot report: A report of conditions from an aircraft in flight. The only source of turbulence and icing observations that comes from inside the weather rather than a model.
UA / UUA Routine / urgent pilot report: The prefix on a coded PIREP. UUA is urgent: severe or extreme turbulence, severe icing, hail, low-level wind shear, tornadoes, or volcanic ash.
NOTAM Notice to Air Missions: Notice of anything about the airspace or airport that a pilot needs and that is not on the chart: closed runways, unserviceable lighting, unusable approaches, temporary restrictions.
TFR Temporary flight restriction: A regulatory NOTAM closing airspace for a period: VIP movement, firefighting, sporting events, disaster relief. Entering one is an enforcement action, not an advisory matter.

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