How to Read METAR and TAF: Decoding Guide for Indian Pilots

What METAR, SPECI and TAF actually are

A METAR is a routine aerodrome weather observation: what the wind, visibility, weather, cloud, temperature and pressure were at a stated time. It is a report of the past, not a forecast. In India, IMD's Standard Operational Procedure for aviation states that METARs are issued at half-hourly intervals, so you will normally see reports timed at 00 and 30 minutes past each hour.

A SPECI is a special observation issued between routine reports when conditions cross specified thresholds, such as visibility or cloud base falling below set values. The format is the same as a METAR. One India-specific point worth knowing: IMD stopped issuing SPECI from 15 November 2015 (00Z), on the reasoning that half-hourly METARs already capture changes. Significant changes are still passed locally to ATC as local special reports, but you will rarely see SPECI in Indian bulletins. SPECI is still in the syllabus.

A TAF (Terminal Aerodrome Forecast) is a forecast for the aerodrome, covering the area within about 8 km of the runway complex according to IMD's SOP. ICAO Annex 3 allows TAF validity periods between 6 and 30 hours.

Decoding a METAR element by element

Elements always appear in a fixed order: report type, station, date and time, wind, visibility, RVR, present weather, cloud, temperature and dew point, QNH, supplementary information, then the trend forecast.

• Report type and station: METAR or SPECI, followed by the four-letter ICAO location indicator. Indian indicators start with V; the second letter shows the FIR (VI Delhi, VA Mumbai, VE Kolkata, VO Chennai). So VIDP is Delhi, VABB is Mumbai, VECC is Kolkata and VOBL is Bengaluru.
• Date and time: six digits plus Z, for example 150600Z means the 15th day of the month at 0600 UTC. Z means UTC, which is IST minus 5 hours 30 minutes, so 0600Z is 1130 IST.
• Wind: three digits of true direction, two or three digits of speed, then the unit, for example 27012KT. Gusts are shown with G, as in 27015G28KT, and are reported when the gust exceeds the mean speed by 10 kt or more. 00000KT means calm.
• Wind variation and VRB: when the direction varies by 60 degrees or more and the mean speed is 3 kt or more, the extremes are added, for example 31012KT 280V350. VRB is used when the variation is 60 degrees or more but the speed is below 3 kt, or when the variation is 180 degrees or more, for example VRB02KT.
• Visibility: four digits in metres. 9999 means 10 km or more, 0000 means less than 50 m. If visibility differs by direction, a minimum value with a compass direction may follow, such as 4000 1200SW, when the minimum is below 1500 m or below half the prevailing visibility and below 5000 m.
• RVR: reported when visibility or RVR is below 1500 m. The format is R, runway designator, slash, value in metres, and an optional tendency letter: U for upward, D for downward, N for no distinct change over the previous 10 minutes. P2000 means more than 2000 m and M0050 means less than 50 m, for example R28/0350D.
• Present weather: an optional intensity sign (minus for light, nothing for moderate, plus for heavy), an optional descriptor, then the phenomenon. Descriptors are MI shallow, BC patches, PR partial, DR low drifting, BL blowing, SH showers, TS thunderstorm and FZ freezing. Precipitation includes DZ drizzle, RA rain, SN snow, GR hail, GS small hail and PL ice pellets. Obscurations include FG fog (visibility below 1000 m), BR mist (1000 m to 5000 m), HZ haze, FU smoke, DU dust and SA sand. Others include SQ squall, DS duststorm, SS sandstorm and FC funnel cloud. VC means in the vicinity, roughly 8 to 16 km from the aerodrome reference point. So +TSRA is a thunderstorm with heavy rain, and VCSH is showers in the vicinity.
• Cloud: amount, then base height in hundreds of feet above aerodrome level. FEW is 1 to 2 oktas, SCT 3 to 4, BKN 5 to 7 and OVC 8. BKN015 is 5 to 7 oktas based at 1,500 ft. CB (cumulonimbus) and TCU (towering cumulus) are the only cloud types named, written straight after the height, as in FEW025CB. When the sky is obscured, vertical visibility is given instead, for example VV002 for 200 ft, or VV/// when it cannot be assessed.
• NSC and NCD: NSC (nil significant cloud) means no cloud below 5,000 ft or the highest minimum sector altitude, whichever is greater, and no CB or TCU, used when CAVOK does not apply. NCD (no cloud detected) is used by automatic observing systems. Because IMD does not use the AUTO indicator, NCD is uncommon in Indian reports.
• Temperature and dew point: whole degrees Celsius separated by a slash, with M for minus, for example 31/24 or M02/M08 at a cold station such as Leh in winter. A small spread warns of fog or low cloud.
• QNH: Q followed by four digits in hectopascals, for example Q1008. IMD's SOP notes that QNH is rounded down to the next whole hectopascal, so 995.6 hPa is reported as Q0995.
• Supplementary information: RE marks recent weather that occurred since the last report but has ended, such as RETSRA. WS followed by a runway, such as WS R27, reports wind shear. IMD's SOP states that remarks (RMK) are not disseminated internationally.

CAVOK: the exact conditions

CAVOK (ceiling and visibility OK) replaces the visibility, RVR, present weather and cloud groups. It may only be used when all of the following are true at the same time.

CAVOK does not mean a clear sky: it can be overcast at 8,000 ft. At an aerodrome where the highest minimum sector altitude is above 5,000 ft, the cloud condition is tied to that higher figure, not to 5,000 ft.

• Visibility is 10 km or more, and no minimum visibility is being reported.
• No cloud below 5,000 ft or below the highest minimum sector altitude, whichever is greater.
• No cumulonimbus (CB) or towering cumulus (TCU) at any height.
• No weather of significance to aviation at or in the vicinity of the aerodrome.

Trend forecasts and TAFs: validity and change groups

Many Indian METARs end with a trend, a short landing forecast valid for 2 hours from the time of the report. NOSIG means no significant change is expected in the next 2 hours. BECMG means conditions are expected to change and stay changed. TEMPO means temporary fluctuations, each expected to last less than an hour, and in total covering less than half the trend period.

Time indicators may follow the change group: FM (from), TL (until) and AT (at), each with four digits of UTC time. For example, BECMG TL0300 0800 FG means visibility becoming 800 m in fog by 0300 UTC. NSW (nil significant weather) is used to show that a weather phenomenon is expected to end.

A TAF starts like a METAR (TAF, station, issue time) and then gives a validity period in day-and-hour format. For example, 2412/2518 means from 1200 UTC on the 24th to 1800 UTC on the 25th, a 30-hour TAF. Next comes the base forecast: wind, visibility, weather and cloud expected at the start of the period. Change groups then modify that picture. A TAF does not carry QNH. TAF AMD means an amended forecast and TAF COR means a corrected one.

• FM followed by day, hour and minute, such as FM250300: a rapid change. From 0300 UTC on the 25th, a completely new set of conditions applies and everything before is superseded.
• BECMG followed by a time window, such as BECMG 2502/2504: a change expected to occur at some point within the window, regular or irregular. ICAO Annex 3 says the window should normally not exceed 2 hours and never exceed 4 hours. Inside the window, plan for the worse of the two.
• TEMPO followed by a window, such as TEMPO 2412/2416: temporary fluctuations, each lasting less than an hour, and together covering less than half of the window. Between these spells, the earlier conditions apply.
• PROB30 and PROB40: a 30 or 40 percent probability of the stated conditions. Only these two values are used. PROB can stand alone or be combined with TEMPO, as in PROB30 TEMPO 2510/2514, but it is not used with BECMG or FM.
• NSW in a change group means the significant weather is expected to end.

Four decoded examples from Indian aerodromes

The reports below are illustrative examples written in the correct format for teaching. They are not real reports and must not be used for any flight.

Example 1, Delhi winter fog: METAR VIDP 120030Z 00000KT 0100 R28/0350D R29L/0300N FG VV001 07/07 Q1020 NOSIG. Decoded: Delhi, 12th, 0030 UTC (0600 IST). Wind calm. Visibility 100 m. RVR runway 28 is 350 m and falling; runway 29L is 300 m with no distinct change. Fog, sky obscured with vertical visibility 100 ft. Temperature and dew point both 7 degrees: saturated air. QNH 1020 hPa. No significant change expected in the next 2 hours.

Example 2, Mumbai monsoon: METAR VABB 150600Z 25018G30KT 220V290 2500 +SHRA FEW010 SCT015 FEW020CB BKN080 26/25 Q1003 TEMPO 1500 TSRA. Decoded: Mumbai, 15th, 0600 UTC (1130 IST). Wind 250 degrees true at 18 kt gusting 30 kt, direction varying between 220 and 290 degrees. Visibility 2,500 m in heavy rain showers. Few at 1,000 ft, scattered at 1,500 ft, few cumulonimbus at 2,000 ft, broken at 8,000 ft. Temperature 26, dew point 25. QNH 1003 hPa. Trend: temporarily visibility 1,500 m in thunderstorm with rain during the next 2 hours.

Example 3, Bengaluru clear morning: METAR VOBL 220330Z 09008KT CAVOK 22/14 Q1018 NOSIG. Decoded: Bengaluru (Kempegowda International), 22nd, 0330 UTC (0900 IST). Wind 090 degrees at 8 kt. CAVOK, so all four CAVOK conditions are met. Temperature 22, dew point 14. QNH 1018 hPa. No significant change expected.

Example 4, Kolkata pre-monsoon TAF: TAF VECC 241100Z 2412/2518 18008KT 5000 HZ SCT020 TEMPO 2412/2415 32025G40KT 2000 TSRA FEW025CB SCT025 BECMG 2416/2418 VRB03KT 3000 BR FM250300 19010KT 6000 NSW SCT020 PROB30 TEMPO 2510/2514 30020G35KT 3000 TSRA FEW030CB. Decoded: Kolkata TAF issued on the 24th at 1100 UTC, valid 1200 UTC on the 24th to 1800 UTC on the 25th. Base: wind 180 degrees at 8 kt, visibility 5,000 m in haze, scattered cloud at 2,000 ft. Temporarily between 1200 and 1500 UTC: wind 320 degrees at 25 kt gusting 40 kt, visibility 2,000 m in thunderstorm with rain, few CB and scattered cloud at 2,500 ft, a typical Nor'wester pattern. Becoming between 1600 and 1800 UTC: variable wind 3 kt, visibility 3,000 m in mist. From 0300 UTC on the 25th: wind 190 degrees at 10 kt, visibility 6 km, no significant weather, scattered at 2,000 ft. Then a 30 percent chance of temporary thunderstorms, gusts 35 kt, between 1000 and 1400 UTC on the 25th.

How Indian reports differ from US (FAA) reports

Much online material follows US practice. India uses the ICAO Annex 3 and WMO formats; for the DGCA exam, always answer in ICAO format.

• Visibility: US METARs use statute miles, such as 3/4SM or 10SM, and P6SM in TAFs. Indian reports use metres, with 9999 for 10 km or more.
• Pressure: US reports give the altimeter setting in inches of mercury, such as A2992. Indian reports give QNH in hectopascals, such as Q1013.
• RVR: US reports give RVR in feet, such as R28L/2600FT. Indian reports use metres.
• Clear sky: US reports use CLR (automated stations, no cloud below 12,000 ft) or SKC. ICAO reports use CAVOK, NSC or NCD instead. CAVOK is not used in US reports.
• Remarks: US METARs carry a long RMK section with sea-level pressure (SLP) and a T group giving temperature to tenths of a degree.
• Trend: Indian METARs at many aerodromes carry a 2-hour trend (NOSIG, BECMG, TEMPO). US METARs do not have trend forecasts.

Where to get official METAR and TAF in India

Aviation meteorological services in India are provided by the India Meteorological Department (IMD) through its Central Aviation Meteorological Division (CAMD), Meteorological Watch Offices (MWOs) and aerodrome meteorological offices. The CAMD website lists METAR, TAF, SIGMET and aerodrome warnings, plus the aviation SOP and manuals.

For pre-flight briefing, IMD runs the On-line Briefing System (OLBS), a web-based briefing service for pilots and flight dispatchers, maintained by the MWOs at New Delhi and Chennai. Its address has changed over the years, so reach it through the CAMD website and confirm with your flying school which source it uses for dispatch. Apps are fine for practice; for flight planning use official IMD products.

Exam tips for the DGCA Meteorology paper

• Convert Z to IST (add 5 hours 30 minutes) and double-check whether a question asks for UTC or local time.
• Memorise all four CAVOK conditions, including the phrase whichever is greater, and remember CAVOK is not a clear sky.
• Know the okta ranges for FEW, SCT, BKN and OVC.
• Separate BR and FG by visibility: below 1000 m is fog, 1000 m to 5000 m is mist.
• Distinguish BECMG (lasting change) from TEMPO (each spell under an hour, total under half the period), and remember PROB uses only 30 or 40.
• Remember the trend is valid for 2 hours, while a TAF validity can run from 6 to 30 hours.
• Practise decoding real Indian reports daily, especially in fog season (December to February) and the monsoon.

Frequently asked questions

• What is the difference between METAR and TAF? A METAR is an observation of current conditions at an aerodrome, while a TAF is a forecast of expected conditions over a validity period of 6 to 30 hours.
• How often are METARs issued in India? IMD issues METARs at half-hourly intervals at Indian aerodromes, according to its aviation SOP.
• Does India still issue SPECI? IMD stopped issuing SPECI from 15 November 2015, though SPECI remains in the syllabus.
• What does CAVOK mean exactly? Visibility 10 km or more, no cloud below 5,000 ft or the highest MSA (whichever is greater), no CB or TCU, and no significant weather at or near the aerodrome.
• What is the difference between BECMG and TEMPO? BECMG is a lasting change that happens within the stated window, while TEMPO describes temporary spells, each under an hour and together less than half the window.
• Is METAR time in IST? No, it is UTC (Z). Add 5 hours 30 minutes for IST.

Useful resources

• IMD Central Aviation Meteorological Division (CAMD)
• IMD Standard Operational Procedure for Aviation Meteorology (PDF)
• IMD CAMD manuals and documents
• Hong Kong Observatory METAR decoding guide (ICAO format)
• Met Office guide to decoding a TAF
• FAA METAR key (US format, for comparison)
• CPLGrid Meteorology subject page
• How to prepare for DGCA CPL exams