Aviation Routine Weather Report

Aviation Routine Weather Report


  • An Aviation Routine Weather Reports (METAR) is a weather observer’s interpretation of the weather conditions at a given site and time
  • Can be used to compare between observed and forecast weather, to determine if conditions are actually developing as originally forecast
  • The U.S. uses the ICAO world standard for aviation weather reporting and forecasting
  • The World Meteorological Organization’s (WMO) publication No. 782 “Aerodrome Reports and Forecasts” contains the base METAR and TAF code as adopted by the WMO member countries



Aviation Weather.gov Raw or Translated METAR Option
Figure 1: Aviation Weather.gov Raw or Translated METAR Option


  • Issued every hour, usually 55~59 past the hour
  • Data may be up to 15 minutes old, should not be older
  • Valid for 1 hour or until the next released report


GROUP 1: Type of Report:

  • METAR (routine)
  • SPECI (special observation)
  • Unscheduled
  • Whenever critical data has changed, it will be updated

GROUP 2: ICAO Station Identifier:

  • In the contiguous 48 States, the 3-letter domestic station identifier is prefixed with a “K”
  • Other prefixes:
    • PA = Alaska
    • PH = Hawaii
    • CU, CW, CY, CZ = Canada
    • MM = Mexico
    • Western Caribbean is “M” followed by the individual country’s letter; i.e., Cuba is “MU” Dominican Republic “MD;” the Bahamas “MY”
    • Eastern Caribbean is “T” followed by the individual country’s letter; i.e., Puerto Rico is “TJ”
    • For a complete worldwide listing see ICAO Document 7910, Location Indicators

GROUP 3: Forecast Times and Report Modifier:

  • Date Time Group (DTG):
    • The first two digits are the date followed with two digits for hour and two digits for minutes (dd/hh/mm)
      • Example: 172345Z (the 17th day of the month at 2345Z)
    • Six-digit date/time group appended with Z to denote the time Coordinated Universal Time (UTC)
    • Observations are required to be started no earlier than 15 minutes prior to reporting time
    • Automated stations get data 10 minutes prior but sky cover is gathered over the preceding 30 minutes
    • Data with the greatest rate of change is evaluated last, assuring the most current data
    • SPECI reports time when the observation took place
  • Modifier:
    • “AUTO” identifies a METAR/SPECI report as an automated weather report with no human intervention
      • If “AUTO” is shown in the body of the report, the type of sensor equipment used at the station will be encoded in the remarks section of the report
        • AO1 for automated weather reporting stations without a precipitation discriminator
        • AO2 for automated stations with a precipitation discriminator
        • A precipitation discriminator can determine the difference between liquid and frozen/freezing precipitation
      • The absence of “AUTO” indicates that a report was made manually by an observer or that an automated report had human augmentation/backup
    • COR indicates a corrected observation
    • The DTG will be the time used in the observation corrected
    • No modifier indicates human observer or automated system with human logged on for oversight functions

GROUP 4: Wind:

  • Reported as 2-minute averages
  • Direction in tens of degrees from true north (first 3 digits)
  • Velocity in whole knots (next 2 digits)
    • Six-digits if wind speed is 3 digits
  • Gusts included at the end with the letter G
  • Wind speed for the most recent 10 minutes is used to determine gusts and maximum peak is reported using two or three digits
  • Velocity appended with KT to indicate knots
  • Other countries use KM / MPH / MPS
  • If wind varies by 60° or more and speed greater than 6 knots, a variable group consisting of the extremes of the wind direction separated by a “v” will follow the prevailing wind group
  • If wind direction is variable and speed 6 knots or less, replace wind direction with VRB, followed by wind speed in knots; or in more rare cases when it is impossible to forecast a single wind direction such as thunderstorms
    • Example: 27010KT
      • Wind from 270 at 10 knots
    • Example: WND 270V350
      • Wind variable 270 to 350
    • Example: 14020KTG30
      • Wind from 140 at 20 knots, gusting to 30 knots
    • Example: 00000KT
      • Winds calm
    • Example: 210103G130KT
      • Wind from 210° at 103 knots with gusts to 130 knots
    • Example: 32012G22KT 280V350
      • Wind 320 at 12 knots, gusting to 22, variable between 280 and 350°
  • Peak Wind: Whenever the peak wind exceeds 25 knots “PK WND” will be included in Remarks, e.g., PK WND 28045/1955 “Peak wind two eight zero at four five occurred at one niner five five.” If the hour can be inferred from the report time, only the minutes will be appended, e.g., PK WND 34050/38 “Peak wind three four zero at five zero occurred at three eight past the hour”
  • Wind shift: Whenever a wind shift occurs, “WSHFT” will be included in remarks followed by the time the wind shift began, e.g., WSHFT 30 FROPA “Wind shift at three zero due to frontal passage”

GROUP 5: Visibility, Weather, and Obstructions to Vision:

  • Prevailing visibility in statue miles (SM)
    • Example: 7SM
      • Seven statute miles
    • Example: 1/2SM
      • One-half statute miles
  • Reported in meters over seas
  • Meters / 1600 = SM
  • M is used to indicate less than one-quarter SM
  • If visibility is less than 7 SM the weather-and-atmosphere/obstruction to vision will also be reported
  • Tower/surface visibility: If either visibility (tower or surface) is below four statute miles, the lesser of the two will be reported in the body of the report; the greater will be reported in remarks
  • Automated visibility: ASOS/AWSS visibility stations will show visibility 10 or greater than 10 miles as “10SM.” AWOS visibility stations will show visibility less than 1/4 statute mile as “M1/4SM” and visibility 10 or greater than 10 miles as “10SM”
    • Automated sites that are augmented by human observer to meet service level requirements can report 0, 1/16 SM, and 1/8 SM visibility increments
  • Variable visibility: Variable visibility is shown in remarks (when rapid increase or decrease by 1/2 statute mile or more and the average prevailing visibility is less than three miles) e.g., VIS 1V2 “visibility variable between one and two”
  • Sector visibility: Sector visibility is shown in remarks when it differs from the prevailing visibility, and either the prevailing or sector visibility is less than three miles
    • Example: VIS N2 – visibility north two
Meters SM
1,600 1
3,200 2
4,800 3
6,400 4
8,000 5
9,600 6
11,200 7
12,800 8
14,400 9
16,000 10
  • Civilian: forecasted prevailing visibility is reported in statute miles (SM)
  • Military: Forecasted prevailing visibility is reported in meters and rounded down to the nearest reportable value
  • Whenever the prevailing visibility is forecasted to be 9,000 meters or less (6 miles or less), the weather or obstructions to vision causing the reduced visibility will be included using the same notation as the METAR
  • 9999 indicates 7 miles visibility or greater is forecasted (unlimited visibility)
  • When appropriate, RVRs will follow immediately after the prevailing visibility
  • If any significant weather or obstruction to vision is forecasted it will be included after visibility using standard codes
  • Omitted if no weather is present

GROUP 6: Runway Visual Range (RVR):

  • A 10 minute RVR evaluation in hundreds of feet
  • A two-digit runway designator with a 4-digit value
    • Example: R28L/2600FT
      • Runway 28L has an RVR of 2600 feet
  • A horizontal visibility as determined from instruments (transmissometer) located alongside and about 14′ higher than runway centerline
  • Calibrated with reference to the sighting of either high-intensity runway lights or the visual contrast of other targets
  • RVR shall only be reported when the equipment is operational
  • Reported whenever the prevailing visibility is 1 SM or less/or the RVR is 6000′ or less
  • RVR measures in 200′ increments to 3000′
  • RVR measures in 500′ increments above 3000′
  • Encoded with an R followed by the 2 digit runway and any R/L/C for the runway (right, left, center)
  • A forward slash divides the runway and the RVR
  • The RVR is appended with FT to indicate feet
  • If variable the two RVRs will be separated with a V
  • M or P indicates a value higher or lower than the reported RVR due to equipment limitations
  • Reference the chart above for meters to SM converting

GROUP 7: Present Weather:

  • May be evaluated instrumentally, manually, or through a combination of methods
  • Present weather is given in the body occurring at the point of observation or within 5 miles from the station
  • VC indicates in the vicinity of 5 to 10 miles
  • Any report beyond 10 miles will be in the remarks
  • Intensity refers to precipitation, not a descriptor (TS or SH)

GROUP 8: Sky Condition:

  • Gives a description of the appearance of the sky including cloud types/layers and sky coverage
  • All sky cover heights are reported in hundreds of feet above the ground level (AGL)
  • Layers will be reported in ascending order up to the first overcast
  • If the layers are below the station (mountainous stations) then /// will be used for height
  • Reported in a 6-character group
  • CLC is used at automated stations when no clouds at or below 12,000′ AGL
  • SKC is used at manual stations when no clouds are reported
  • When the sky is partially obscured the amount of sky cover hidden will be reported and then a remark will give details
  • When the sky is totally obscured, only VV will be reported
  • For obscured sky:
    • VV = vertical visibility
    • VV is in hundreds of feet as well
    • More than 1 layer may be reported
  • Clouds may be followed by another modifier:
    • T = towering
    • CU = cumulus
    • CB = cumulonimbus

GROUP 9: Temperature/Dew Point:

  • Reported in whole degrees Celsius
  • 2 digits separated by a solidus (/)
  • Sub-zero values are prefixed with an M
  • If the temperature and dew point are not available, they wont be reported
  • If only the temperature is available, it will be coded, ending with a /
  • To convert between Celsius and Fahrenheit, visit the conversion page

GROUP 10: Altimeter:

  • Altimeter setting (in U.S. reports) is always prefixed with an A
  • Indicates inches of mercury reported using 4 digits

GROUP 11: Remarks:

  • Noted with an RMK
  • There are 3 basic categories:
    • Manual and automated remarks
    • Plain language remarks, and
    • Additive data and maintenance remarks
  • Includes clarifying or augmented data

Reporting Prevailing Visibility

  • Surface (horizontal) visibility is reported in METAR reports in terms of statute miles and increments thereof; e.g., 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4, 7/8, 1, 1 1/8, etc. (Visibility reported by an un-augmented automated site is reported differently than in a manual report, i.e., ASOS/AWSS: 0, 1/16, 1/8, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/2, 3, 4, 5, etc., AWOS: M1/4, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4, 2, 2 1/2, 3, 4, 5, etc.) Visibility is determined through the ability to see and identify preselected and prominent objects at a known distance from the usual point of observation. Visibilities which are determined to be less than 7 miles, identify the obscuring atmospheric condition; e.g., fog, haze, smoke, etc., or combinations thereof
  • Prevailing visibility is the greatest visibility equaled or exceeded throughout at least one half of the horizon circle, not necessarily contiguous. Segments of the horizon circle which may have a significantly different visibility may be reported in the remarks section of the weather report; i.e., the southeastern quadrant of the horizon circle may be determined to be 2 miles in mist while the remaining quadrants are determined to be 3 miles in mist
  • When the prevailing visibility at the usual point of observation, or at the tower level, is less than 4 miles, certificated tower personnel will take visibility observations in addition to those taken at the usual point of observation. The lower of these two values will be used as the prevailing visibility for aircraft operations

Estimating Intensity of Rain and Ice Pellets

  • Rain:
    • Light: From scattered drops that, regardless of duration, do not completely wet an exposed surface up to a condition where individual drops are easily seen
    • Moderate: Individual drops are not clearly identifiable; spray is observable just above pavements and other hard surfaces
    • Heavy: Rain seemingly falls in sheets; individual drops are not identifiable; heavy spray to height of several inches is observed over hard surfaces
  • Ice Pellets:
    • Light: Scattered pellets that do not completely cover an exposed surface regardless of duration. Visibility is not affected
    • Moderate: Slow accumulation on ground. Visibility reduced by ice pellets to less than 7 statute miles
    • Heavy: Rapid accumulation on ground. Visibility reduced by ice pellets to less than 3 statute miles

Estimating Intensity of Snow or Drizzle (Based on Visibility)

  • Light: Visibility more than 1/2 statute mile
  • Moderate: Visibility from more than 1/4 statute mile to 1/2 statute mile
  • Heavy: Visibility 1/4 statute mile or less