METAR Decoder

• How to use the METAR decoder?
• What is a METAR?
• What is a METAR used for?
• Where does METAR data come from?
• How accurate is a METAR?
• How to read a METAR?
• METAR examples
• METAR flight categories (VFR, MVFR, IFR, LIFR) explained
• METAR weather phenomena codes
• Runway State Group (RSG)
• Automated Surface Observation System (ASOS) and Automated Weather Observation System (AWOS)
• Aerodrome colour state
• Airmen's Meteorological Information (AIRMET) and Significant Meteorological Information (SIGMET)
• Pilot Report (PIREP)
• METARs for drone pilots and FAA Part 107
• METAR abbreviations and codes
• Using METAR for flight planning
• Frequently asked questions about METARs

The station identifier is a four-character ICAO aerodrome designator that identifies the airport or weather reporting station where the observation was made. In the example METAR, the station identifier is KBOS. KBOS is the ICAO code for Boston Logan International Airport.

ICAO station identifiers always contain four characters. The first character or group of characters indicates the region or country, while the remaining characters identify the specific aerodrome. The station identifier is always the first operational element of a METAR because every weather observation must be associated with a specific location.

For pilots, this field confirms that the weather report belongs to the intended departure, destination, or alternate airport.

The observation time indicates exactly when the weather observation was recorded. In the example METAR, the observation time is 271454Z. This six-digit group follows the format DDHHMMZ, where DD is the day of the month, HH is the hour in UTC, MM is the minute, and Z denotes Zulu time (UTC). Therefore, 271454Z means the 27th day of the month at 14:54 UTC.

All METARs worldwide use UTC to eliminate confusion between local time zones. The day-of-month reference requires pilots to be aware of the current date to correctly interpret the observation time, particularly around midnight transitions.

Before using a METAR, pilots should always verify that the observation is sufficiently recent for flight planning and operational decision-making. Most routine METARs are issued hourly, while SPECI reports are issued when significant changes occur between routine observations.

The report modifier indicates whether the observation was made automatically by instruments or by a human observer, and whether it has been corrected. In the example METAR, the modifier is AUTO, indicating that the observation was generated entirely by automated sensors with no human augmentation.

AUTO means that no human observer was present to supplement, verify, or augment the automated measurements. Certain weather phenomena — such as freezing precipitation, ice pellets, or volcanic ash — may not be detectable by automated sensors. When AUTO is present, pilots should apply additional caution when interpreting weather phenomena, particularly in conditions where human observation would add significant value.

The modifier COR (corrected) indicates that this METAR supersedes and corrects a previously issued report for the same station and observation time. If no modifier is present, the observation was made by a human observer or a human-augmented automated station.

The wind group reports the surface wind direction and speed at the time of observation. In the example METAR, the wind group is 27018G25KT. This indicates wind from 270 degrees magnetic at 18 knots, with gusts to 25 knots.

The format is DDDffGffKT, where DDD is the wind direction in degrees TRUE north (not magnetic — this is an important distinction from runway headings which use magnetic north), ff is the sustained wind speed, G indicates gusts are present, the second ff is the peak gust speed, and KT denotes knots. Wind direction 270 means the wind is coming from due west. When wind direction is variable and the speed is 3 knots or less, the direction group is reported as VRB (e.g. VRB03KT). Calm wind — no measurable wind — is reported as 00000KT. Wind speed may be reported in knots (KT), kilometres per hour (KMH), or metres per second (MPS) depending on the country of origin, though KT is the most common unit in international aviation.

Wind direction and speed are averaged over the 10-minute period immediately preceding the observation. Gusts are reported only when the maximum wind speed exceeds the mean wind speed by 10 knots or more during that period — if gusts do not meet this threshold, the G group is omitted even if brief speed variations occurred. For extreme wind conditions exceeding 99 knots, the value is preceded by P and reported as P99KT (or P99MPS / P199KPH in other units). For pilots, the wind group is critical for runway selection, crosswind component calculation, takeoff and landing distance planning, and fuel planning. The gust value represents the maximum wind speed observed during the past 10 minutes and must be evaluated against the aircraft’s demonstrated crosswind limit.

The variable wind direction group reports the range of wind directions when the wind direction has varied by 60 degrees or more during the past 10 minutes and the mean wind speed is 3 knots or more. In the example METAR, the variable wind direction group is 210V270, indicating that the wind direction has varied between 210 degrees and 270 degrees.

The format is dddVddd, where the first ddd is the extreme clockwise direction and the second ddd is the extreme counterclockwise direction, separated by the letter V. This group always follows the wind group when present.

Variable wind directions are operationally significant for pilots because they indicate unstable or rotating wind conditions at the aerodrome. A wide directional range can result in significant changes in the crosswind component during approach, rollout, or takeoff.

The prevailing visibility group reports the greatest visibility that is reached or exceeded throughout at least half of the horizon circle. In the example METAR, the prevailing visibility is 2500, which in ICAO format represents 2,500 metres.

In ICAO international METARs, visibility is reported in metres for values below 10 kilometres. The value 9999 indicates visibility of 10 km or more. The value 0000 indicates visibility of less than 50 metres — the minimum measurable value. When visibility is 10 km or more and other CAVOK conditions are met, the entire visibility, weather, and cloud group may be replaced by CAVOK. In US domestic METARs, visibility is reported in statute miles and fractions (e.g. 1 1/2SM, 10SM). This example uses the ICAO format, indicating the station is reporting in metric units consistent with ICAO Annex 3.

A visibility of 2,500 metres places this observation within the Instrument Flight Rules (IFR) category. Pilots should cross-check this value against the applicable minima for the planned approach procedure.

The runway visual range group reports the maximum distance along a specific runway at which a pilot can see and identify high-intensity runway lights or other visual markers. In the example METAR, R04R/1200FT indicates an RVR of 1,200 feet on Runway 04 Right.

The format is RDDd/VVVVi, where R identifies the group, DD is the runway designator, d is the parallel runway indicator (L for left, R for right, C for centre), VVVV is the visual range value, and i is the trend (U for increasing, D for decreasing, N for no change). When the RVR exceeds the maximum measurable range, the value is prefixed with P (e.g. P6000FT). When below the minimum, it is prefixed with M.

RVR is the primary reference for determining whether Category I, II, or III instrument approach minimums are met. An RVR of 1,200 feet is below the standard Category I ILS minimum of 1,800 feet, indicating conditions are below Cat I minimums at Runway 04R at the time of this observation.

The present weather group describes the type, intensity, and characteristics of weather phenomena observed at or near the aerodrome at the time of the observation. In the example METAR, the present weather group is +RA, indicating heavy rain.

The format combines an optional intensity qualifier (- for light, no qualifier for moderate, + for heavy), an optional descriptor (TS for thunderstorm, SH for shower, FZ for freezing, BL for blowing, DR for drifting, MI for shallow, PR for partial, BC for patches), and one or more phenomenon codes (RA for rain, SN for snow, DZ for drizzle, FG for fog, BR for mist, HZ for haze, FU for smoke, SA for sand, DU for dust, GR for hail, GS for small hail, PL for ice pellets, UP for unknown precipitation). Multiple phenomena can be combined in a single group (e.g. TSRA for thunderstorm with rain, FZRA for freezing rain).

Additional combined codes worth noting: FZFG (freezing fog) indicates fog with temperature at or below 0°C, creating icing conditions on exposed surfaces and aircraft. PY (spray) is reported at coastal or marine aerodromes when wind-driven water spray is reducing visibility. Present weather directly affects visibility, braking action, flight safety, and aircraft performance. Heavy rain (+RA) reduces visibility, can affect aircraft systems, and requires active weather radar interpretation for en-route and approach planning.

The sky condition group reports cloud coverage, height, and type for each significant cloud layer. In the example METAR, the sky condition is BKN025CB, indicating a broken layer of cumulonimbus cloud with a base at 2,500 feet AGL.

Sky condition is reported using coverage descriptors: FEW (1-2 oktas, 1/8 to 2/8 coverage), SCT scattered (3-4 oktas), BKN broken (5-7 oktas), and OVC overcast (8 oktas). Not all cloud layers are reported — the selection follows a strict rule: (1) the lowest layer regardless of coverage, (2) the next lowest layer of SCT or more, (3) the next higher layer of BKN or more, and (4) significant convective cloud (CB or TCU) if not already included. This explains why a METAR may appear to skip certain layers — only operationally significant layers meeting these criteria are included. Height is expressed in hundreds of feet above ground level (AGL) — BKN025 means broken clouds at 2,500 ft AGL. Cloud type is appended when significant: CB (cumulonimbus) and TCU (towering cumulus) are the only two cloud type designators used in standard METARs. CBMAM (cumulonimbus mammatus) may appear in remarks at augmented stations — mammatus clouds are associated with severe thunderstorms and downdraft activity. The ceiling is defined as the lowest BKN or OVC layer.

BKN025CB is significant because cumulonimbus clouds indicate the presence of thunderstorm activity, with associated turbulence, icing, lightning, and wind shear. A broken ceiling at 2,500 feet places the aerodrome below VFR minimums in most jurisdictions, and the CB designation requires pilots to assess thunderstorm avoidance procedures. When the sky is completely obscured and cloud layers cannot be observed, sky condition is replaced by vertical visibility, reported as VVfff where fff is the vertical visibility in hundreds of feet (e.g. VV008 = 800 ft vertical visibility). Three additional sky condition codes are used in specific circumstances: SKC (sky clear) is used by human observers when there are no clouds; CLR is used by ASOS/AWOS stations when no clouds are detected below 12,000 feet; and NSC (no significant cloud) is the ICAO equivalent, used internationally when there are no clouds below 5,000 feet, no cumulonimbus, and no TCU.

The temperature and dew point group reports the air temperature and dew point temperature at the time of the observation, both in degrees Celsius. In the example METAR, 08/06 indicates a temperature of 8°C and a dew point of 6°C.

The format is TT/TdTd, where TT is the temperature and TdTd is the dew point. Negative values are prefixed with M (minus), for example M05/M08. Temperatures are rounded to the nearest whole degree Celsius in standard METARs; more precise values are available in the T-group remark.

The small difference between temperature (8°C) and dew point (6°C) indicates high relative humidity and a high probability of fog or low cloud formation if the temperature drops further. Pilots use temperature and dew point to assess icing risk, fog likelihood, density altitude, and the likelihood of convective activity.

The altimeter setting group reports the current atmospheric pressure reduced to sea level, used to set the aircraft altimeter so that it reads the correct altitude above mean sea level. In the example METAR, the altimeter setting is Q1008, indicating a QNH of 1008 hectopascals (hPa).

The Q prefix indicates the value is in hectopascals (hPa), the standard unit used in ICAO international METARs worldwide. The A prefix is used in US domestic METARs and reports the altimeter setting in inches of mercury (e.g. A2992 means 29.92 inHg). A QNH of 1008 hPa is below the standard atmosphere value of 1013.25 hPa, indicating lower than standard pressure at this aerodrome.

Pilots must set the correct QNH before descent and approach to ensure the altimeter accurately reads altitude above sea level. An incorrect altimeter setting can result in the aircraft being significantly lower or higher than indicated, which is critical during approach to minimums.

The trend forecast is an ICAO element that provides a short-term forecast of significant weather changes expected within the two-hour period following the observation time. In the example METAR, NOSIG indicates that no significant changes are expected to any weather element during that period.

The trend forecast is appended to METARs at ICAO-compliant stations worldwide. It is not included in US domestic METARs. The possible values are NOSIG (no significant change), BECMG (conditions gradually changing to those specified, change expected to persist), and TEMPO (temporary conditions expected for periods of less than one hour each and less than half the total period). BECMG and TEMPO groups include the specific changed elements using the same wind, visibility, weather, and cloud format as the METAR body.

NOSIG is operationally reassuring for pilots planning to depart or arrive within the next two hours, indicating the reporting officer does not expect conditions to change significantly. However, the trend forecast does not replace a TAF and should not be used as the sole basis for flight planning decisions. PROB30 and PROB40 may also appear in trend forecasts at some stations, indicating a 30% or 40% probability of the specified conditions occurring — PROB30 is not used in US METARs but appears in many international ICAO reports. BECMG and TEMPO groups may be qualified with time references using FM (from), TL (until), or AT (at) followed by a UTC time group — for example BECMG FM1030 TL1130 means the change begins from 10:30 and completes by 11:30 UTC. The abbreviation NSW (No Significant Weather) is used within a trend forecast to indicate that previously reported significant weather is expected to end — for example BECMG NSW means conditions are becoming no significant weather.

The remarks section identifier RMK marks the boundary between the standard ICAO METAR body and the supplementary remarks section used primarily in US domestic METARs. Everything following RMK is part of the remarks section and is not part of the standard ICAO METAR format.

The RMK identifier is defined in FAA Order JO 7900.5D and is used exclusively in US domestic aviation. International METARs using ICAO format do not include an RMK section. The remarks section contains additional observational data that supplements the standard fields, including more precise values, sensor status information, and non-automated observations.

When using METARs outside the United States, pilots should not expect an RMK section. When operating within the US, the RMK section often contains operationally significant information that supplements the standard fields, including peak winds, sea-level pressure, and automated station equipment status.

The AO1 and AO2 remarks identify the type of automated observing station and its precipitation detection capability. In the example METAR, AO2 indicates an automated station equipped with a precipitation discriminator.

AO1 means the station is automated but does not have a precipitation discriminator — it can detect precipitation occurring but cannot distinguish between liquid and frozen precipitation types. AO2 means the station has a precipitation discriminator and can distinguish between rain, snow, and other precipitation types. This distinction is important for interpreting precipitation type reports from automated stations.

When an AO1 remark is present, pilots should be aware that precipitation type reports (rain, snow, etc.) may be less reliable than those from AO2 stations or human-augmented observations.

The peak wind remark reports the highest wind gust speed recorded at the station since the previous METAR observation, along with the direction and time of that gust. In the example METAR, PK WND 28032/1420 indicates a peak gust from 280 degrees true at 32 knots, observed at 14:20 UTC.

The format is PK WND dddff/HHmm, where ddd is the wind direction in degrees true (note: peak wind direction is reported in degrees TRUE rather than magnetic), ff is the peak gust speed in knots, and HHmm is the UTC time of the peak gust. The time reference uses only hours and minutes — the date is assumed to be the same as the observation.

The peak wind is operationally significant because it represents the most extreme wind condition recorded during the observation period. A peak gust of 32 knots from 280 degrees, combined with the reported sustained wind of 270 degrees at 18 knots gusting to 25 knots, indicates a period of significantly stronger wind activity that has since moderated.

The surface visibility remark reports the prevailing visibility at the surface, typically used when visibility varies significantly with height or when tower visibility differs from surface visibility. In the example METAR, SFC VIS 10 indicates a surface visibility of 10 statute miles.

Surface visibility is reported when an automated system detects, or a human observer notes, that the surface visibility differs from the prevailing visibility reported in the standard body of the METAR. In this case, the prevailing visibility reported in the METAR body is 2,500 metres (ICAO format), while the surface visibility is 10 statute miles — a significant discrepancy that may indicate the reduced visibility aloft is due to precipitation or a shallow layer of weather.

For pilots on approach, the surface visibility can be more operationally relevant than tower visibility in certain conditions, particularly when flying through precipitation or cloud layers that reduce visibility at altitude but not at the surface.

The precipitation begin and end time remark records the times at which specific precipitation types began or ended during the observation period. In the example METAR, DZE36RAB36E39 indicates that drizzle ended at 36 minutes past the hour, rain began at 36 minutes past the hour, and rain ended at 39 minutes past the hour.

The format uses the precipitation code (DZ for drizzle, RA for rain, SN for snow, etc.) followed by B for began or E for ended, then the time in minutes past the hour (HHmm for the full UTC time, or mm alone for within the current hour). Multiple begin and end times for the same precipitation type can appear in sequence.

This remark is operationally useful for understanding the recent history of precipitation at the aerodrome and can help pilots assess whether active precipitation is currently present, recently ended, or beginning again.

The lightning remark describes the frequency, type, and location of lightning observed at or near the aerodrome. In the example METAR, OCNL LTGICCC DSNT E indicates occasional lightning, with cloud-to-cloud and cloud-to-cloud (intracloud) strokes, distant, to the east.

Lightning frequency descriptors include OCNL (occasional, less than 1 flash per minute), FRQ (frequent, 1-6 flashes per minute), and CONS (continuous, more than 6 flashes per minute). Lightning type codes include IC (intracloud), CC (cloud-to-cloud), CG (cloud-to-ground), and CA (cloud-to-air). Location is described by compass direction and distance qualifiers: DSNT (distant, more than 10 miles), VC (vicinity, within 5-10 miles of the aerodrome), or no qualifier (at the aerodrome).

Lightning is a direct indicator of active thunderstorm activity. For pilots, the direction and distance of lightning relative to the aerodrome is critical for assessing whether it is safe to operate, approach, or depart. Cloud-to-ground lightning is particularly hazardous during ground operations.

The sea-level pressure remark reports the current atmospheric pressure reduced to mean sea level, expressed in hectopascals (hPa), to a higher resolution than the QNH field in the METAR body. In the example METAR, SLP958 indicates a sea-level pressure of 995.8 hPa.

The SLP value is encoded as a three-digit number representing the last three digits of the pressure in tenths of hectopascals. To decode: if the first digit is 0 to 4, prefix with 10 (e.g. SLP023 = 1002.3 hPa). If the first digit is 5 to 9, prefix with 9 (e.g. SLP958 = 995.8 hPa). This compressed format avoids the need to transmit the leading digits that are almost always either 9 or 10.

Sea-level pressure is used for synoptic meteorological analysis, pressure system identification, and altimetry cross-checking. A value of 995.8 hPa confirms the low-pressure conditions associated with the adverse weather in this observation.

The T-group remark provides temperature and dew point to the nearest tenth of a degree Celsius, offering higher precision than the whole-degree values reported in the METAR body. In the example METAR, T01220028 decodes to a temperature of 12.2°C and a dew point of 2.8°C.

The format is T s T T T s d d d, where the first digit (s) is the sign of the temperature (0 for positive, 1 for negative), the next three digits are the temperature in tenths of degrees (0122 = 12.2°C), the fifth digit is the sign of the dew point (0 for positive, 1 for negative), and the last three digits are the dew point in tenths of degrees (0028 = 2.8°C). Note: the T-group values here differ from the METAR body values (08/06) because the T-group reflects the most current sensor reading at the time of report transmission.

The T-group is primarily used for meteorological analysis and post-flight weather data. Pilots rarely use this level of temperature precision operationally, but it can be useful when making precise density altitude or icing-risk calculations.

The 6-hour maximum temperature remark reports the highest temperature recorded during the 6-hour period ending at the observation time. In the example METAR, 10231 decodes to a maximum temperature of 23.1°C.

The format is 1sTTT, where 1 identifies the group as a maximum temperature, s is the sign (0 for positive, 1 for negative), and TTT is the temperature in tenths of degrees Celsius. Therefore, 10231 means: 1 (maximum temp group), 0 (positive), 231 = 23.1°C. This remark is included in METARs issued at 0000, 0600, 1200, and 1800 UTC.

The 6-hour maximum temperature provides context for the diurnal temperature cycle and is used in synoptic meteorological analysis. For flight operations, it can help assess the likelihood of convective development when surface heating is a factor.

The 6-hour minimum temperature remark reports the lowest temperature recorded during the 6-hour period ending at the observation time. In the example METAR, 20089 decodes to a minimum temperature of 8.9°C.

The format is 2sTTT, where 2 identifies the group as a minimum temperature, s is the sign (0 for positive, 1 for negative), and TTT is the temperature in tenths of degrees Celsius. Therefore, 20089 means: 2 (minimum temp group), 0 (positive), 089 = 8.9°C. Like the maximum temperature group, this remark appears in METARs issued at 0000, 0600, 1200, and 1800 UTC.

Together with the maximum temperature group, the minimum temperature provides the 6-hour temperature range, which is useful for assessing diurnal variation, frost risk, and the potential for rapid temperature changes that could affect visibility and precipitation type.

The pressure tendency remark describes how the sea-level pressure has changed over the 3 hours preceding the observation, including the characteristic of change and the magnitude of that change. In the example METAR, 53036 indicates a pressure that was falling then rising (characteristic 3), with a net 3-hour change of 3.6 hPa.

The format is 5appp, where 5 identifies the pressure tendency group, a is the characteristic of change (0 = increasing then steady, 1 = increasing, 2 = increasing then decreasing, 3 = decreasing then increasing, 4 = steady, 5 = decreasing then steady, 6 = decreasing, 7 = decreasing then increasing, 8 = steady or increasing then decreasing), and ppp is the pressure change in tenths of hectopascals over the past 3 hours.

Pressure tendency is a key indicator of approaching or departing weather systems. A rapidly falling pressure typically signals the approach of a low-pressure system, frontal passage, or deteriorating weather conditions. Two additional remarks — PRESFR (pressure falling rapidly) and PRESRR (pressure rising rapidly) — are reported when pressure changes are occurring rapidly at the time of observation, independent of the 5appp tendency group. PRESFR and PRESRR are standalone remarks that alert pilots and dispatchers to dynamic pressure changes that may indicate rapidly evolving weather.

The precipitation accumulation remark reports the amount of liquid precipitation that has fallen during a specified period. In the example METAR, 60015 indicates 0.15 inches of precipitation accumulated during the past 6 hours.

The format is 6RRRR, where 6 identifies the group, and RRRR is the precipitation amount in hundredths of an inch. A value of 0015 represents 0.15 inches. This group is reported in METARs at 0000, 0600, 1200, and 1800 UTC for 6-hour accumulations. For 24-hour accumulations, the format uses the 7RRRR group.

Precipitation accumulation data helps pilots assess the potential for waterlogged runways, braking action advisories, and standing water conditions. In winter operations, it provides a basis for assessing runway contamination when combined with temperature data.

This coded remark group provides additional observational data from automated weather sensors. In FAA METAR format, multi-digit remark groups encode various supplementary observations including cloud layer data, sensor readings, and coded weather summaries that supplement the standard METAR body fields.

Complex coded groups in the remarks section may include snow depth (4/sss format), cloud-type identifications, and other non-standard remark elements encoded according to FAA Order JO 7900.5D. These groups require reference to the full FAA METAR code table for precise interpretation and are primarily used for meteorological data exchange and archival purposes rather than direct pilot briefing.

Pilots are not expected to decode complex coded remark groups manually. METAR decoder tools, weather services, and dispatchers use software to interpret these groups. The operationally relevant information they contain is typically summarised in other, more readable remark fields.

The 24-hour temperature extremes remark reports the maximum and minimum temperatures recorded during the 24-hour period ending at midnight UTC. In the example METAR, 413230322 decodes to a 24-hour maximum temperature of 32.3°C and a minimum of 3.2°C. Note: these values reflect the encoded data and are used for synoptic weather record purposes.

The format is 4sTTTsTTT, where 4 identifies the group, the first sTTT encodes the maximum temperature with its sign, and the second sTTT encodes the minimum temperature. This remark appears only in the 0000 UTC METAR, as it summarises the full preceding 24-hour period.

The 24-hour temperature extremes are primarily used for climatological records and synoptic analysis. For flight operations, the minimum temperature is relevant for assessing overnight frost risk, cold-soak effects on aircraft systems, and the potential need for de-icing or anti-icing.

The virga remark indicates that precipitation is falling from clouds but evaporating before reaching the ground. In the example METAR, VIRGA DSNT SE indicates virga observed at a distance, to the southeast of the aerodrome.

Virga is visually observed as streaks or wisps of precipitation trailing from cloud bases that do not reach the surface. It occurs when the lower atmosphere is sufficiently dry or warm to evaporate the falling precipitation before it reaches the ground. Virga is always reported with a direction and optionally a distance qualifier (DSNT for distant, VC for in the vicinity).

Virga is operationally significant because it is associated with microburst risk. The evaporating precipitation cools and accelerates the descending air, potentially creating a strong downdraft that can turn into a microburst at lower altitudes. Pilots should treat virga as a wind shear and microburst hazard, particularly during approach and departure.

The ACSL remark reports the presence of altocumulus standing lenticular clouds, observed here at a distance to the west of the aerodrome. Lenticular clouds form in the crests of mountain or terrain-induced standing waves and indicate significant turbulence in the associated wave system.

Standing lenticular clouds are stationary relative to the terrain that generates them, even as air passes through them continuously. ACSL (altocumulus standing lenticular) forms at mid-levels. The lower equivalent is SCSL (stratocumulus standing lenticular) and the upper is CCSL (cirrocumulus standing lenticular). All are indicators of mountain wave activity.

Pilots flying near ACSL should anticipate moderate to severe turbulence, particularly in the rotor zone below the wave crest. Mountain wave turbulence can extend hundreds of miles downwind and at altitudes far above the mountain tops. The DSNT qualifier indicates the wave activity is currently not directly over the aerodrome but is present in the vicinity.

PWINO indicates that the present weather identifier sensor — the automated instrument that detects and classifies precipitation type — is inoperative at the time of the observation. This means the automated station is unable to identify or report precipitation type.

When PWINO is present in the remarks, any precipitation type information in the METAR body (such as +RA in this example) may have been derived from a different sensor or may be absent. The inoperative status means the station cannot differentiate between rain, drizzle, snow, ice pellets, or freezing precipitation automatically.

For pilots, PWINO is a significant qualification on the METAR. When the precipitation identifier is inoperative, reports of precipitation type are unreliable, and additional sources of weather information — such as pilot reports (PIREPs), radar, and adjacent METAR stations — should be used to determine actual precipitation type and associated hazards.

TSNO indicates that the automated lightning detection equipment is not operating at the station, meaning the METAR is unable to include thunderstorm detection or lightning observation data in the remarks section.

When TSNO is present, pilots cannot rely on the METAR remarks to provide lightning or thunderstorm information from this station. The absence of thunderstorm remarks in the METAR body or remarks section does not mean there is no thunderstorm activity in the area — it means the equipment to detect it is not functioning.

When operating in areas where TSNO is reported, pilots should obtain thunderstorm and lightning information from other sources including onboard weather radar, ADS-B weather services, pilot reports, and adjacent stations. TSNO combined with PWINO — as in this example — means both precipitation type and thunderstorm detection are unavailable, significantly limiting the reliability of weather type information in the METAR.

The dollar sign symbol at the end of the METAR remarks section indicates that the automated weather observing system requires maintenance. Two additional rapid-change remarks may appear: SNINCRG indicates snow is increasing rapidly on the ground, typically observed when snow depth is increasing by 1 inch or more in 15 minutes. NOSPECI indicates that special METAR (SPECI) reports are not issued at this station regardless of weather changes. One or more sensors or system components at the station have generated a maintenance alert, indicating a potential reliability issue with the observation data.

The $ symbol does not identify which specific sensor or component requires maintenance. It is a general flag that the system has detected an anomaly. In the context of this example METAR, the $ indicator appears alongside PWINO and TSNO, confirming that multiple sensors are either inoperative or requiring attention.

When $ is present, pilots should treat the entire METAR with additional caution. The maintenance flag means the observation may be incomplete, inaccurate, or missing data from one or more fields. Cross-checking with adjacent stations, pilot reports, radar, and other weather products is strongly recommended when making operational decisions based on a METAR marked with $.

The recent weather group reports significant weather phenomena that were present at the aerodrome within the past hour but are no longer occurring at the time of the observation. It is a standard ICAO METAR field defined in ICAO Annex 3 and appears between the altimeter setting and the trend forecast.

The format is RE followed by the standard weather descriptor and phenomenon codes — for example, RERA (recent rain), RETS (recent thunderstorm), REFZRA (recent freezing rain), REBLSN (recent blowing snow). Multiple recent weather groups can appear in sequence. The RE prefix is the only distinguishing feature; the weather codes that follow use exactly the same format as the present weather field.

Recent weather is operationally significant because it informs pilots about conditions that may have left residual effects — wet or icy runways following recent rain or snow, reduced braking action following recent freezing precipitation, or turbulence and wind shear associated with a recent thunderstorm that has since moved away from the aerodrome. RE groups are used in ICAO international METARs but are not standard in US domestic METARs.

The wind shear group is a supplementary ICAO METAR field that warns pilots of significant wind shear conditions on the approach or departure path for a specific runway. It appears after the altimeter setting and is not part of the standard US domestic METAR format.

The format is WS followed by a runway designator. A specific altitude layer may also be included. For example, WS R04R indicates wind shear on the approach or departure path to Runway 04 Right. WS ALL RWY indicates wind shear is present on all runway approach and departure paths. The group may specify whether the wind shear is on takeoff (TKOF) or landing (LDG). When altitude is included, it appears as WS followed by the altitude in hundreds of feet and the runway designator.

Wind shear on approach or departure paths is one of the most hazardous conditions in aviation and is a leading contributor to approach and landing accidents. The WS group in a METAR provides a direct warning that the instrument approach or departure procedure for the affected runway may be affected by a sudden change in wind speed or direction. Pilots should treat any METAR containing a WS group with extreme caution and obtain the latest pilot reports before commencing the approach.

The wind shift remark reports the time at which a significant wind direction change of 45 degrees or more occurred at the station, with the wind speed remaining at 6 knots or more both before and after the shift. In this example, WSHFT 1715 indicates a wind shift was observed at 17:15 UTC.

Wind shifts are often associated with the passage of a front, outflow boundary from a thunderstorm, or sea breeze. They are operationally significant because a wind shift can rapidly change the crosswind or headwind component on the active runway, affect wake turbulence behaviour, and signal a sudden change in weather conditions.

When a wind shift is reported in the METAR remarks, pilots and ATC should expect that runway conditions may have changed since the last routine observation. Approach and departure planning should account for the post-shift wind direction and speed.

The variable ceiling height remark is reported when the ceiling — the lowest BKN or OVC layer — is below 3,000 feet and the ceiling height is variable. In this example, CIG 013V017 indicates the ceiling is varying between 1,300 and 1,700 feet AGL.

The format is CIG hhhVhhh, where the first value is the lowest observed ceiling height and the second is the highest, both in hundreds of feet AGL. A secondary ceilometer location may also report a ceiling difference: CIG hhh RWYnn indicates the ceiling height at a specific runway location differs from the value in the METAR body.

Variable ceilings are particularly hazardous during instrument approaches. A ceiling that fluctuates across the decision height (DH) or minimum descent altitude (MDA) means conditions are intermittently below minimums. Pilots should obtain the latest ATIS and consider whether a stabilised approach is achievable before committing to the final approach segment.

The variable prevailing visibility remark is reported when the prevailing visibility is below 3 statute miles and varies significantly during the observation period. In this example, VIS 3/4V1 1/2 indicates visibility varies between three-quarters of a mile and one and a half statute miles.

The format is VIS vnvnVvxvx, where the first value is the lowest observed visibility and the second is the highest, separated by V. A secondary location visibility may also be included: VIS vvv RWYnn reports visibility at a specific runway when it differs from the prevailing visibility — for example VIS 3/4 RWY11 means visibility at Runway 11 is three-quarters of a mile.

Variable visibility near approach or landing minimums requires particular caution. When visibility is oscillating around the published minimum, pilots must be prepared to execute a missed approach if the required visual reference is not established at the decision point. Variable visibility may indicate fog patches, precipitation cells, or blowing obscurants moving through the aerodrome.

The tower visibility remark reports the visibility as observed from the airport control tower by tower personnel, when this differs from the prevailing visibility reported by the automated surface sensor in the METAR body. For example, TWR VIS 2 indicates tower personnel observed a visibility of 2 statute miles.

Tower visibility and surface visibility (SFC VIS) serve complementary roles. SFC VIS is reported by the ASOS sensor at its installation point on the airfield. TWR VIS is observed by tower personnel who may have a different vantage point and can observe conditions in specific directions or at different heights. When the two values differ significantly, both are included in the remarks.

For instrument approaches, tower visibility may be used in place of prevailing visibility in certain circumstances per FAA regulations. Pilots should note which value applies to their intended approach when both TWR VIS and SFC VIS appear in the remarks.

The hourly precipitation amount remark reports the liquid precipitation accumulated since the last METAR observation, in hundredths of an inch. In this example, P0003 indicates 0.03 inches of precipitation has fallen since the previous hourly report.

The format is Prrrr where rrrr is the amount in hundredths of an inch. A trace amount — precipitation detected but too small to measure — is reported as P0000. This differs from the 6-hour precipitation group (6RRRR reported in sections at 00, 06, 12, and 18 UTC) and the 24-hour group (7RRRR reported at 12 UTC), which accumulate over longer periods.

The hourly precipitation group helps pilots assess the rate of precipitation accumulation at the aerodrome. Rapidly accumulating precipitation can indicate standing water on runways, reduced braking effectiveness, and deteriorating visibility, particularly in convective conditions.

The tornadic activity remark is an augmented observation — added by a human observer — that reports the occurrence of a tornado, funnel cloud, or waterspout at or near the aerodrome. The remark identifies the type of activity, the time it began and ended, its location relative to the station, and its direction of movement.

The format includes the phenomenon type (TORNADO, FUNNEL CLOUD, or WATERSPOUT), begin time (B followed by minutes past the hour), location (compass direction from the station), and movement (MOV followed by direction). For example, TORNADO B25 N MOV E means a tornado was observed beginning at 25 minutes past the hour, located to the north of the station, moving eastward.

Tornadic activity in a METAR remarks section represents one of the most extreme weather hazards in aviation. Any METAR containing TORNADO or WATERSPOUT should be treated as an immediate operational alert. Ground operations should be suspended, aircraft secured, and personnel sheltered. PIREPs and SIGMETs should be checked immediately for the affected area.

The 24-hour precipitation amount remark reports the total liquid precipitation accumulated over the 24-hour period ending at the 12 UTC observation. In this example, 70015 indicates 0.15 inches of precipitation over the past 24 hours.

The format is 7RRRR where 7 identifies the group and RRRR is the amount in hundredths of an inch. This group appears only in the 12 UTC METAR. It complements the 6-hour group (6RRRR) and the hourly group (Prrrr) by providing a full-day precipitation summary. A trace is reported as 70000.

The 24-hour precipitation total provides context for assessing cumulative runway contamination, soil saturation, and flooding risk. For airport operations, it is particularly relevant when combined with temperature data to assess whether accumulated precipitation may have frozen overnight or is contributing to standing water conditions.

Example 1 — Chicago O'Hare (KORD)

Example 2 — Los Angeles International (KLAX)

Example 3 — Seattle-Tacoma International (KSEA)

Example 4 — complex METAR with remarks (KBOS)

VFR (Visual Flight Rules)

VFR is a METAR flight category where ceiling is above 3,000 feet and visibility is greater than 5 statute miles. It represents good weather conditions suitable for visual flying with minimal restrictions.

MVFR (Marginal Visual Flight Rules)

MVFR is a METAR flight category where ceiling is between 1,000 and 3,000 feet and/or visibility is between 3 and 5 statute miles. It indicates reduced visual margins but conditions may still support visual flight.

IFR (Instrument Flight Rules)

IFR is a METAR flight category where ceiling is between 500 and 999 feet and/or visibility is between 1 and less than 3 statute miles. It requires pilots to fly using instrument procedures instead of visual references.

LIFR (Low Instrument Flight Rules)

LIFR is a METAR flight category where ceiling is below 500 feet and/or visibility is below 1 statute mile. It represents very poor weather conditions requiring precision instrument approaches.

METAR Intensity Codes

METAR intensity codes describe the strength or proximity of weather phenomena reported at the time of observation. They indicate whether conditions are light, moderate, heavy, or occurring in the vicinity of the aerodrome.

METAR Weather Descriptors

METAR descriptor codes provide additional detail about how weather phenomena are occurring, such as whether they are shallow, patchy, freezing, or associated with thunderstorms or showers.

METAR Precipitation Codes

METAR precipitation codes identify the type of falling water or ice particles observed at the airport, such as rain, snow, drizzle, hail, or ice pellets.

METAR Obscuration and Atmospheric Phenomena Codes

METAR obscuration and atmospheric phenomena codes describe conditions that reduce visibility or affect the atmosphere. METAR obscuration codes include fog, haze, smoke, dust, sand, volcanic ash, and other visibility-reducing phenomena.

Runway identification (Digits 1–2)

The first two digits of the Runway State Group identify the runway affected and include special coding rules for parallel runways and system-wide reporting. Single runway numbers are used directly (e.g. 27), parallel runways are encoded by adding 50 to the right-hand runway (e.g. 18L = 18 and 18R = 68), 88 indicates that all runways are affected, and 99 indicates that no new information has been received and the previous report is repeated.

Runway surface deposit type (Digit 3)

The third digit of the Runway State Group describes the type of surface contamination present on the runway, such as water, snow, ice, slush, or dry conditions. This digit is critical for understanding the physical condition of the runway surface. The table below lists the standardized codes used for the third digit of the Runway State Group and their corresponding runway surface deposit types.

Runway contamination coverage (Digit 4)

Digit four of the Runway State Group indicates how much of the runway is covered by contamination. It expresses the percentage of runway surface affected, ranging from minimal coverage to complete coverage. The table below lists the standardized codes used for the fourth digit of the Runway State Group and their corresponding contamination coverage percentages.

Runway deposit depth (Digits 5–6)

Digits five and six of the Runway State Group indicate the depth of the surface deposit in millimetres or centimetres. This information helps determine braking performance and aircraft stopping distance. The table below lists the standardized codes used for digits five and six of the Runway State Group and their corresponding deposit depth values.

Runway friction and braking action (Digits 7–8)

The final two digits of the Runway State Group represent runway friction or braking action. These values provide an indication of how slippery the runway is and how effectively an aircraft can decelerate. The table below lists the standardized codes used for digits seven and eight of the Runway State Group and their corresponding friction and braking action values.

When contamination ceases and a runway has been cleared, CLRD replaces the deposit, extent, and depth digits. For example: 24CLRD93 = Runway 24 cleared, braking action medium/good. 88CLRD95 = All runways cleared, braking action good.

What can ASOS and AWOS not detect?

Without human augmentation, automated systems may not reliably detect or report freezing precipitation, ice pellets, volcanic ash, drizzle at some stations, or certain obscuration types. Thunderstorm identification may also be limited without the TSNO sensor. When these sensor limitations are active, appropriate remarks (PWINO, TSNO, FZRANO, RVRNO) appear in the METAR to alert pilots.

When are ASOS/AWOS observations unusable?

An ASOS/AWOS observation must not be used as an authorised weather observation if either the visibility or wind is reported as missing. Additionally, an ASOS/AWOS observation cannot be used for the purpose of initiating or conducting an instrument approach if the altimeter setting is reported as missing, unless an approved alternate source is noted on the applicable approach chart.

AO1 vs AO2 stations

The AO1 and AO2 remarks distinguish between two types of automated stations. AO1 stations do not have a precipitation discriminator and cannot distinguish between rain and snow. AO2 stations have a precipitation discriminator and can differentiate between liquid and frozen precipitation types. When operating in mixed precipitation or near-freezing temperature conditions, the AO1 or AO2 designation is critical for assessing the reliability of reported precipitation type.

What is an AIRMET?

An AIRMET (Airmen's Meteorological Information) is a weather advisory issued for meteorological conditions of moderate intensity that may affect the safety of all aircraft operations over a defined area.

An AIRMET is issued for hazardous weather of moderate intensity expected to cover an area of at least 3,000 square miles. AIRMETs use the designators Sierra (S), Tango (T), and Zulu (Z).

• •Sierra: IFR conditions — ceilings below 1,000 ft and/or visibility below 3 SM affecting 50% or more of an area, or mountain obscuration
• •Tango: Moderate turbulence, sustained surface winds of 30 kt or more
• •Zulu: Moderate icing and freezing level heights

What is a SIGMET?

A SIGMET (Significant Meteorological Information) is a weather advisory issued for severe or extreme meteorological conditions considered hazardous to all aircraft operating over a wide area.

A SIGMET is issued for severe or extreme hazards covering at least 3,000 square miles. SIGMETs are either convective or non-convective.

• •Convective SIGMETs: Severe thunderstorms, embedded thunderstorms, tornadoes, hail ≥3/4 inch, wind gusts ≥50 kt
• •Non-convective SIGMETs: Severe or extreme turbulence, severe icing, widespread dust/sandstorms below 3 SM visibility, volcanic eruption or ash

Why must METARs be used alongside AIRMETs and SIGMETs?

METARs provide an hourly snapshot of actual surface weather at specific airports, while AIRMETs and SIGMETs identify widespread hazardous en-route conditions. Pilots must use them together to bridge the gap between local conditions and regional hazards, ensuring complete situational awareness and safe aeronautical decision-making. There are three key reasons why using these weather products in tandem is essential for safe flight:

When is a PIREP required?

A PIREP is not strictly mandated by federal aviation regulations for every flight. However, pilots are required to provide one when requested by ATC, and it is considered essential safety practice to submit a PIREP whenever unforecast weather or hazardous conditions are encountered.

When ATC is required to solicit a PIREP?

ATC is required to request PIREPs when any of the following conditions are reported or forecast in the area:

• •Ceilings at or below 5,000 feet
• •Surface or in-flight visibility of 5 miles or less
• •Thunderstorms and related phenomena
• •Moderate turbulence or greater
• •Light icing or greater
• •Any reported or forecast wind shear
• •Volcanic eruptions, ash clouds, or sulphur gases

Routine (UA) vs urgent (UUA) PIREPs

PIREPs are classified as either routine or urgent. Pilots should file routine PIREPs for operationally useful conditions such as cloud bases and tops, winds aloft that differ from forecasts, or conditions that are better than forecast. Urgent PIREPs must be filed immediately upon encountering severe or extreme turbulence, severe icing, tornadoes or funnel clouds, hail, low-level wind shear, or volcanic ash.

How to submit a PIREP?

PIREPs can be relayed directly to ATC over the radio during an active flight, reported to a Flight Service Station (FSS) by radio or phone, or submitted electronically via the NOAA Aviation Weather Center's ADDS system before or after flight.

What does a PIREP contain?

A routine PIREP uses the prefix UA and an urgent PIREP uses UUA. Key elements include:

• •/OV — location (fix or airport identifier)
• •/TM — time (UTC)
• •/FL — altitude or flight level
• •/TP — aircraft type
• •/SK — sky cover and cloud bases/tops
• •/WX — flight visibility and weather
• •/TA — temperature (Celsius)
• •/WV — wind direction and speed
• •/TB — turbulence intensity and type
• •/IC — icing intensity and type
• •/RM — remarks (free text)

How do PIREPs supplement a METAR?

PIREPs provide the crucial missing third dimension in aviation weather by transforming localized, two-dimensional ground data into a comprehensive picture of the actual flying environment. While a METAR is a static, surface-level snapshot, PIREPs add real-time intelligence from the cockpit that no ground sensor can replicate. They are uniquely valuable in four key ways:

• •Vertical weather profiling: PIREPs are the only way to directly observe in-flight phenomena such as cloud tops, icing levels, and the exact altitude and intensity of turbulence — none of which surface sensors can measure.
• •Automated system failures: When a METAR is degraded by sensor limitations — such as PWINO, TSNO, or a fully unaugmented AUTO station — PIREPs become essential to fill the gaps that automated systems cannot report.
• •In-flight situational awareness: Ground sensors cannot measure winds at cruise altitude or detect invisible hazards such as localised wind shear. PIREPs are the only real-time source for these conditions.
• •Forecast verification: Meteorologists and dispatchers rely on pilot reports to confirm, refine, or amend active hazardous weather advisories such as AIRMETs and SIGMETs.

PIREP example decoded

The following example shows a complete PIREP in raw coded format followed by its plain-English decoded meaning, illustrating how each element maps to an operational weather condition.

Routine PIREP over Boston at 15:00 UTC, flight level 8,000 ft, Boeing 737. Broken cloud base 5,500 ft tops 8,000 ft. Flight visibility 5 SM in light rain. Temperature +4°C. Light turbulence. Light rime icing. Remark: low-level wind shear on final approach.

FAA weather minimums for drone operations

Under FAA Part 107, remote pilots must maintain a minimum flight visibility of 3 statute miles from their ground control station. A METAR provides the current visibility at the nearest reporting station, which is the primary reference for this determination.

Part 107 also limits operations to daylight hours or civil twilight with anti-collision lighting. METARs help assess cloud cover, precipitation, and visibility conditions that may affect safe operations even within these hours.

What to look for in a METAR before a drone flight?

• •Visibility — must be at least 3 SM from your control station
• •Wind speed and gusts — assess effect on stability and control
• •Ceiling — lowest BKN or OVC layer indicates cloud base height
• •Present weather — precipitation, fog, thunderstorms
• •Flight category — VFR conditions preferred; MVFR/IFR warrants caution
• •Remarks — TSNO, PWINO, and $ flags indicate sensor limitations

Scenario 1: VFR route planning

You are planning a VFR flight into Colorado Springs (KCOS). Before departure, you pull the destination METAR and decode each element:

Scenario 2: Runway selection and crosswind assessment

You are departing Chicago Midway (KMDW). The airport has runways oriented roughly 04/22 and 13/31. The wind group reads 23015G28KT — wind from 230° at 15 knots, gusting to 28 knots.

Scenario 3: Density altitude and takeoff performance

Eagle County Regional Airport (KEGE) sits at 6,548 ft MSL. The METAR shows a temperature of 34°C and an altimeter setting of 30.02 inHg. This combination has significant performance implications.

Scenario 4: Reading remarks to identify sensor limitations

This METAR from Bismarck, North Dakota carries several remarks that change how the entire report should be interpreted. Each remark flag is an operational qualifier, not just supplementary data.