METAR and TAF Decoding

METAR and TAF are concise textual formats used for transmitting weather reports and forecasts for aviation purposes. The codes are not very complex, but they contain elements which may be hard to decipher for a layman. The following is intended as an unofficial reference for reading the codes. I initially wrote this page for myself as an aid for learning METAR decoding. The information has been collected from various web sites around the Internet.

METAR Messages

METAR is a report describing the current weather conditions at a location. A METAR message consists of several space-separated groups of alphanumerical characters, describing various aspects of the present weather: wind, visibility, temperature etc. Here is what a METAR looks like:

UEEE 072000Z 00000MPS 0150 R23L/0500 FG VV003 M50/M53 Q1028

This rather extreme example is an actual observation made at the airport of the Siberian city of Yakutsk on 2004-12-07 at 20:00 UTC. After having learned how to decode METARs, you will probably agree that Yakutsk is one of the coldest cities on Earth! See Wx-Now for current extreme temperatures around the world.

The following table describes the components of a METAR message, group by group. A minimal METAR contains information about wind, visibility, clouds, temperature and pressure in addition to observing location and issuing time. Other phenomena are reported when needed.

Group	Format	Explanation	Example
Station Identifier	`CCCC`	`CCCC`: the four-letter ICAO code for the observing location	`EFHK`
Date and Time	`YYGGggZ`	`YY`: day of month `GGgg`: hours (00–23) and minutes (00–59), in UTC `Z`: Denotes UTC time.	`101450Z`
Report Modifier	`AUTO` or `COR`	`AUTO`: The report was made automatically without human intervention or supervision. `COR`: The report was corrected.	`COR`
Wind	`dddffKT` or `dddffGf_mf_mKT`	`ddd`: Wind direction (true heading), rounded to nearest ten degrees and always expressed as three digits. Direction can be given as `VRB` if wind direction is variable and wind speed is at most 3 knots. `ff`: Average wind speed of last 10 minutes in knots. `f_mf_m`: Maximum gust wind speed in knots. If it is calm, the wind is given as `00000KT`. In addition to knots, wind speed may also be indicated in meters per second or kilometers per hour. In that case, `MPS` or `KMH` will be used instead of `KT`.	`03004KT`
Variable Wind Direction	`d_nd_nd_nVd_xd_xd_x`	`d_nd_nd_n`: The left extreme of wind direction. `d_xd_xd_x`: The right extreme of wind direction. This field is used if the total variation of wind direction during the last 10 minutes is 60° or more and wind speed is more than 3 knots. The direction extrema are given in clockwise order.	`360V080`
Horizontal Visibility	`VVVV` or `VVVVD_v` or `VVVVD_v V_xV_xV_xV_xD_v`	`VVVV`: The minimum horizontal visibility in meters. If the visibility is better than 10 km, `9999` is used. `9999` means a minimum visibility of 50 m or less. `V_xV_xV_xV_x`: The maximum horizontal visibility in meters. `D_v`: In case of marked directional variation in visibility, the approximate direction of minimum and maximum visibility is given as one of eight compass points (`N`, `SW`, …) Usually, only the minimum visibility is reported. If the minimum is less than 1500 m and the maximum is over 5000 m, the maximum visibility and its direction are indicated by a second visibility group following the minimum visibility. In the United States, visibility is given in statutes miles and fractions. In that case, format `VVVVVSM` is used.	`5000NW`
Runway Visual Range	`RD_RD_R/V_RV_RV_RV_Ri` or `RD_RD_R/V_RV_RV_RV_RVV_RV_RV_RV_Ri`	`D_RD_R`: Runway designator. Parallel runways are distinguished by appending `L`, `C` or `R` to runway designator. `V_RV_RV_RV_R`: Runway visibility in meters. If the visibility varies significantly, both minimum and maximum values are specified, separated by `V`. Prefixes `P` (plus) and `M` (minus) indicate the actual value being greater or smaller than the maximum or minimum measurable value. `i`: The tendency of visibility change can be indicated by `D` (down), `U` (up) or `N` (no change).	`R10/1000VP1800D`
Present Weather	`w′w′`	`w′w′`: Description of a weather phenomenon, consisting of following components: Qualifier, either `-` (light), `+` (heavy) or `VC` (in vicinity, i.e. not on location but within 8000 m) Descriptor `MI`: Shallow `BC`: Patches `PR`: Partial `DR`: Drifting `BL`: Blowing `SH`: Showers `TS`: Thunderstorm `FZ`: Freezing Precipitation `DZ`: Drizzle `RA`: Rain `SN`: Snow `SG`: Snow grains `IC`: Ice crystals `PL`: Ice pellets `GR`: Hail `GS`: Small hail / snow pellets `UP`: Unknown Obscuration `BR`: Mist (visibility > 1000 m) `FG`: Fog (visibility < 1000 m) `FU`: Smoke `VA`: Volcanic ash `DU`: Widespread dust `SA`: Sand `HZ`: Haze `PY`: Spray Other `PO`: Well developed dust/sand whirls `SQ`: Squall `FC`: Funnel cloud `+FC`: Tornado / water spout `SS`: Sandstorm `DS`: Dust storm	`-RA BCFG BR`
Clouds	`N_sN_sN_sh_sh_sh_s` or `VVh_sh_sh_s` or `SKC` or `NSC` or `CLR`	`N_sN_sN_s`: Cloud amount. One of the following: `FEW`: Few (1/8–2/8) `SCT`: Scattered (3/8–4/8) `BKN`: Broken (5/8–7/8) `OVC`: Overcast (8/8) `VV`: The sky is obscured. `h_sh_sh_s`: Height of cloud base or the extent of vertical visibility (`VV`) in hundreds of feet above field elevation. If height was not measured, `///` is used instead. `SKC`: Sky clear. `NSC`: No significant clouds. There are no clouds below 1500 m and no Cumulonimbus at any height. `CLR`: No clouds below 3600 m (used in automatic observations). If a cloud layer consists of Cumulonimbus or towering Cumulus, `CB` or `TCU` is appended after cloud base height.	`FEW010 SCT020CB BKN070`
CAVOK	`CAVOK`	Short for “Ceiling and visibility OK”. The visibility, weather and cloud groups can be replaced by CAVOK if the following conditions are fulfilled: Visibility is 10 km or better No clouds below 5000 ft No Cumulonimbus at any altitude No significant weather phenomena (see Present Weather above).	`CAVOK`
Temperature and Dew Point	`T′T′/T′_dT′_d`	`T′T′`: The temperature rounded to nearest whole degree Celsius. `T′_dT′_d`: The dew point rounded to nearest whole degree Celsius. Negative temperature or dew point is indicated by prefix `M`.	`04/M02`
Pressure	`QP_HP_HP_HP_H`	`P_HP_HP_HP_H`: The mean sea level pressure (“QNH”) in hectopascals (hPa). In some countries like United States and Canada, pressure is given in inches and hundredths. In such reports, prefix `Q` is replaced by `A`.	`Q0996`
Recent Weather	`REw′w′`	`w′w′`: Weather phenomenon code (see Present Weather above)	`RETSRA`
Wind Shear	`WS RWYD_RD_R` or `WS ALL RWY`	`D_RD_R`: Runway designator, see Runway Visual Range.	`WS RWY11L`
Trend	Consists of following keywords and other METAR components.	`BECMG`: Becoming `TEMPO`: Temporarily `NOSIG`: No significant change expected in 2 hours `AT`: At `FM`: From `TL`: Until	`BECMG -SHRA SCT030CB TEMPO 4000 RADZ BKN010`
Remarks	`RMK` followed by METAR components and miscellaneous abbreviations.		`RMK WIND 850 FT 29015 KT`

METAR Runway Report

METAR reports may include runway reports which contain information about snow/water coverage and friction coefficient. A runway report consists of eight digits in five groups (R_RR_RE_RC_Re_Re_RB_RB_R) with the following interpretation:

R_RR_R E_R C_R e_Re_R B_RB_R

Runway designator. The numerical identifier of the runway in question. 88 means all runways, 99 indicates repetition of previous report.

If there are two parallel runways, the right one is indicated by adding 50 to its number. For example, runway 04L (or 04) is denoted by 04, whereas 54 means runway 04R.

Type of deposit on runway.

0: Clear and dry
1: Damp
2: Wet or puddles
3: Frost
4: Dry snow
5: Wet snow
6: Slush
7: Ice
8: Compacted snow
9: Frozen ridges
/: Not reported

Extent of deposit.

1: 1–10 %
2: 11–25 %
5: 26–50 %
9: 51–100 %

Depth of deposit.

00: Less than 1 mm
01…90: The depth in millimeters
92: 10 cm
93: 15 cm
94: 20 cm
95: 25 cm
96: 30 cm
97: 35 cm
98: 40 cm
99: Runway not in use

Friction coefficient or braking action

01…90: Friction coefficient times 100. For example, 37 indicates a friction coefficient of 0.37.
91: Poor braking action
92: Poor/medium braking action
93: Medium braking action
94: Medium/good braking action
95: Good braking action
99: Unreliable measurement
//: Not given

Note: CLRD may replace elements t, e and dd if the runway has been cleared of deposits. For example, 54CLRD95 means runway 04R cleared, braking action good.

TAF Messages

Whereas METAR describes the current weather conditions, a TAF message contains forecast information. Many of the elements are similar to those used in METARs. An example of a (short) TAF message:

EFHK 171627Z 180018 33004KT 9999 FEW040 TX22/12Z TN10/02Z

The first two groups (EFHK 171627Z) are identical to METAR groups: location identifier and issuing day & time.

The third group (180018) tells the period for which the forecast is given. The first two numbers denote day of month. The next four numbers give the validity hours. In this example, the forecast is valid from midnight to 18:00. After these code groups, a description of the forecast weather phenomena follows.

The following table contains keywords characteristic for TAF messages. Remember that in TAFs and METARs all times are given in UTC.

Group	Explanation
`BECMG aabb`	A gradual change in weather between `aa` and `bb` hours.
`TEMPO aabb`	Temporary (less than 60 min) changes in weather between `aa` and `bb` hours.
`FMhhmm`	A quick (in less than 60 min) change in weather occurring at `hh` hours and `mm` minutes.
`TLhhmm`	A change in weather by `hh` hours and `mm` minutes.
`AThhmm`	A change in weather occurring at `hh` hours and `mm` minutes.
`PROB pp`	Following weather will take place with a probability of `pp` percent.
`NSW`	No significant weather.
`Ttt/hhZ`	The temperature is predicted to be `tt` degrees Celsius at `hh` hours.
`TXtt/hhZ`	The maximum temperature is predicted to be `tt` degrees Celsius at `hh` hours.
`TNtt/hhZ`	The minimum temperature is predicted to be `tt` degrees Celsius at `hh` hours.

Other TAF groups are similar to those found in METARs.

METAR and TAF data access

The U.S. National Weather Service provides access to METAR and TAF reports at their Aviation Digital Data Service site.