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WMO-782 - Aerodrome Reports and Forecasts - Users Handbook to METAR-TAF Codes (2020)

Reproduced for study. Always verify against the official GACAR at gaca.gov.sa.

Ask Captain Adel about this

WMO-No. 782WMO-No. 782For more information, please contact:

World Meteorological Organization

7 bis , avenue de la Paix – P.O. Box 2300 – CH 1211 Geneva 2 – Switzerland

Strategic Communications Office

Tel.: +41 (0) 22 730 87 40/83 14 – Fax: +41 (0) 22 730 80 27

Email: communications@wmo.int

public.wmo.int

Aerodrome Reports and Forecasts – A Users’ Handbook to the CodesAerodrome

Reports

and Forecasts

A Users’ Handbook to the CodesJN 20644

WEATHER CLIMATE WATER

Aerodrome Reports and

Forecasts

A Users’ Handbook to the Codes

2020 edition

WMO-No. 782WEATHER CLIMATE WATER

WMO-No. 782

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is reserved by WMO. Short extracts from WMO publications may be reproduced

without authorization, provided that the complete source is clearly indicated. Editorial

correspondence and requests to publish, reproduce or translate this publication in part

or in whole should be addressed to:

Chair, Publications Board

World Meteorological Organization (WMO)

7 bis, avenue de la Paix Tel.: +41 (0) 22 730 84 03

P.O. Box 2300 Fax: +41 (0) 22 730 81 17

CH-1211 Geneva 2, Switzerland Email: publications@wmo.int

ISBN 978-92-63-10782-4

NOTE

The designations employed in WMO publications and the presentation of material in

this publication do not imply the expression of any opinion whatsoever on the part of

WMO concerning the legal status of any country, territory, city or area, or of its authorities,

or concerning the delimitation of its frontiers or boundaries.

The mention of specific companies or products does not imply that they are endorsed

or recommended by WMO in preference to others of a similar nature which are not

mentioned or advertised .

FOREWORD

This booklet is a simple guide to the aeronautical meteorological codes, METAR,

SPECI and TAF , applicable as of 5 November 2020, updated as a result of the

alignment of the Technical Regulations (WMO-No. 49), Volume II – Meteorological

Service for International Air Navigation, Parts I and II, with Amendment 79 to

Annex 3 to the Convention on International Civil Aviation. It is aimed at a wide

range of users such as pilots, flight dispatchers, air traffic control staff and

meteorological observers at smaller aerodromes where sophisticated automated

instruments are not available. Although the readers of this handbook may not

be professional meteorologists, it is assumed that they have some formal

meteorological training.

The handbook answers basic questions on the preparation of meteorological

reports and forecasts, such as:

– The information to be included;

– The order to be used;

– How the information is to be encoded and decoded.

At the end of the booklet, explanations of weather phenomena significant to

aviation are provided. For more details on the codes, the relevant sections of

the WMO Manual on Codes (WMO-No. 306) on METAR, SPECI and TAF should

be consulted.

METAR and SPECI are still being encoded mainly based on human weather

observations. Although instruments are increasingly being used, the observer

continues to play a major and important part in ensuring that prepared weather

reports satisfy the stated requirements. Nevertheless, certain limitations should

be understood. For instance, when visibility is 10 km or more, the observer at

the usual observing site, even at larger airports, should be able to see and report

clouds over a wide area, including some distance on the approach. If visibility

is, for instance, only 2 000 m, the field of vision is greatly reduced and patches

of low cloud on the approach may not be seen or so reported.

Aerodrome forecasts, in TREND and TAF forms, are not intended to provide

detailed descriptions of the weather during the forecast period. The first part

of the TAF gives the forecaster’s assessment of the most likely forecast values at

the start of the forecast period. Any changes that take place during the forecast

period are indicated only if the changes are significant. Significant changes are

defined as a result of full discussions with the International Civil Aviation

Organization (ICAO) and the aviation users.

PART A

AVIATION WEATHER REPORTS – METAR AND SPECI

METAR is the name of the code for an aerodrome routine weather report. A

METAR is issued at hourly or half-hourly intervals.

SPECI is the name of the code for an aerodrome special weather report. A

SPECI can be issued at any time when certain criteria are met (see

Technical Regulations (WMO-No. 49), Volume II, Part II, Appendix 3,

section 2.3).

Both METAR and SPECI have the same code form and both may have a TREND

forecast appended (see Part B (page 29)).

METAR or SPECI contains the following information in the order shown:

IDENTIFICATION GROUPS

SURFACE WIND

PREVAILING VISIBILITY

RUNWAY VISUAL RANGE (if available)

PRESENT WEATHER

CLOUD (or vertical visibility if appropriate)

AIR AND DEWPOINT TEMPERATURE

PRESSURE – QNH

SUPPLEMENTARY INFORMATION

MISSING ELEMENTS

Notes:

1. The code word CAVOK is used to replace the visibility, present weather and cloud

groups when the three following conditions are simultaneously met:

– Visibility is 10 km or more;

– There is no cloud below 1 500 m (5 000 ft) or below the highest minimum

sector altitude, whichever is greater, and no cumulonimbus;

– There is no significant weather phenomenon as contained in Code table 4678

(reproduced on page 13) of the Manual on Codes (WMO-No. 306), Volume I.1,

Part A – Alphanumeric codes, section C.

2. At the end of a METAR or SPECI , a remarks section starting with the code word RMK

may be appended. This section contains information required by a national authority

and, as such, this information is not disseminated internationally.

CODE FORMAT

METAR

or COR CCCC YYGGgg Z NIL AUTO

SPECI

ENCODE SO FAR

SPECI LUDO 211025Z

1. IDENTIFICATION GROUPS

This section will have three parts:

– The report code name ( METAR or SPECI ).

– The ICAO location indicator of the reporting station, for example, LUDO .

– The day of the month and the time of observation in hours and minutes

UTC (coordinated universal time), followed by the letter Z .

Notes:

1. The code words COR and NIL are inserted after the code name and the time group,

respectively, as appropriate.

2. The code word AUTO is inserted when the report contains a fully automated

observation, that is without human intervention.

The encode on the opposite page reads:

Aerodrome special report at LUDO on 21 of the month at 10 h and 25 min UTC,

being the time of occurrence of the change.

CODE FORMAT

dddff Gfmfm KT

dndndnVdxdxdx or

MPS

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

2. SURFACE WIND

Normally, there will be a five-figure group to indicate the 10-min mean wind

followed by an abbreviation to indicate the wind speed units used, where KT

denotes knots and MPS denotes metres per second. The first three figures

indicate the wind direction, and the last two the wind speed.

Examples: 31015KT

27006MPS

The surface wind direction and speed shall be reported in steps of 10° true and

1 kt, respectively. Any observed value which does not fit the reporting scale in

use shall be rounded to the nearest step in the scale.

Additionally, if, during the 10 min preceding the observation, the maximum

gust speed has exceeded the mean speed by 10 kt (5 m s–1) or more, this gust

will be reported by inserting the letter G followed by the gust speed directly

after the mean speed.

Example: 31015G27KT

If, during the 10 min immediately preceding the observation, the wind direction

has varied by 60° or more but less than 180° and the mean wind speed is 3 kt

(2 m s–1) or more, the two extreme directions should be indicated in clockwise

order, with the letter V inserted between the two directions.

Example: 31015G27KT 280V350

Notes:

1. The wind reported should be the mean over the 10 min preceding the observation.

If during this period there has been a marked discontinuity lasting at least 2 min,

the mean values should be assessed over the period after the discontinuity. A marked

discontinuity occurs when there is a wind direction change of 30° or more with a

wind speed of 10 kt (5 m s–1) or more, before or after the change, or a wind speed

change of 10 kt (5 m s–1) or more.

2. The averaging period for measuring variations from the mean wind speed (gusts)

should be 3 s.

This page intentionally left blank.

Special cases

Variable : The wind direction is encoded as VRB only if one of the following

conditions is met:

(a) The wind speed is less than 3 kt (2 m s–1).

Example: VRB02KT

(b) The wind speed is higher and wind direction is varying by 180° or more

and a single direction is impossible to determine, for example when a

thunderstorm is over the aerodrome.

Example: VRB28KT

Calm : When a wind speed is less than 1 kt (0.5 m s–1), the group is encoded as

00000 followed by the abbreviation for the wind speed units.

Example: 00000KT

Speeds of 100 kt (50 m s–1) or more : The wind speed shall be preceded by the

letter indicator P and reported as P99 KT (P49 MPS ).

Example: 240P99KT

CODE FORMAT

V V V V

or VNVNVNVNDv

CAVOK

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW

3. VISIBILITY

The group V V V V shall be used to report prevailing visibility. When horizontal

visibility is not the same in different directions, and when visibility is fluctuating

rapidly and the prevailing visibility cannot be determined, the group V V V V shall

be used to report the lowest visibility.

Example: Prevailing visibility of 4 000 m is encoded as 4000 .

When visibility sensors are used in such a manner that no directional variations

can be given, the abbreviation NDV shall be appended to the visibility reported.

The reporting scales of visibility are as follows:

(a) In steps of 50 m if V V V V is less than 800 m;

(b) In steps of 100 m if V V V V is 800 m or more, but less than 5 km;

(d) As 10 km when visibility is 10 km or more.

Directional variation in visibility VNVNVNVNDv

When the visibility is not the same in different directions and when the minimum

visibility is different from the prevailing visibility, and less than 1 500 m or less

than 50 per cent of the prevailing visibility, the group VNVNVNVNDv shall also be

used to report the minimum visibility and its general direction.

Example: 1400SW means that the minimum visibility equals 1 400 m with

SW as its general direction.

If the minimum visibility is observed in more than one direction, then Dv shall

represent the most operationally significant direction.

Exception

When the minimum visibility is less than 1 500 m and the visibility in another

direction is more than 5 000 m, the maximum visibility and its direction should

also be reported.

Example: 1400SW 6000N (1 400 m to the south-west and 6 km to the north)

If the maximum visibility is observed in more than one direction, then the most

operationally significant direction is reported.

CODE FORMAT

RDRDR/VRVRVRVRi

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW R24/P2000

4. RUNWAY VISUAL RANGE

Where the runway visual range (RVR) can be determined and when it is reported,

the group starts with the letter R followed by the runway designator DRDR

and / followed by the RVR in metres. Up to a maximum of four groups may be

reported.

Example: R24/1100 (runway visual range on runway 24, 1 100 m)

Special cases

When the RVR is assessed to be more than 2 000 m, it should be reported as

P2000 .

Examples: R24/P2000 (runway visual range on runway 24, greater than

2 000 m)

R24/1800 (prevailing visibility less than 1 500 m, RVR assessed

to be 1 800 m)

When the RVR is below the minimum value that can be assessed, the RVR should

be reported as M followed by the appropriate minimum value that can be

assessed.

Example: R24/M0150 (runway visual range on runway 24, less than 150 m)

The reporting scales of RVR are as follows:

(a) Increments of 25 m, if RVR is less than 400 m;

(b) Increments of 50 m, if RVR is between 400 and 800 m;

Observed values are rounded down to the nearest lower step of the scale.

Note: For commercial operations many users consider runway visual range to be the

most important and critical information. Therefore, where there is the required

instrumentation capable of assessing and displaying 1-, 2-, 5- and 10-min mean values,

the variations and the tendency of the change are required. The tendency is indicated

by i, as follows:

(a) i = U when the runway visual range has increased during the 10 min preceding the

observation;

(b) i = D when the runway visual range has decreased;

(d) When it is not possible to determine a tendency, i is omitted.

CODE FORMAT

w’w’

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW R24/P2000 +SHRA

5. PRESENT WEATHER

Code table 4678 ( Manual on Codes , WMO-No. 306)

QUALIFIER WEATHER PHENOMENA

Intensity or

proximityDescriptor Precipitation Obscuration Other

– Light

Moderate

(no

qualifier)

+ Heavy

(well-

developed

in the case

of dust/

sand whirls

(dust

devils)

and funnel

clouds)

VC In the

vicinityMI Shallow

BC Patches

PR Partial

(covering

part of the

aerodrome)

DR Low drifting

BL Blowing

SH Shower(s)

TS Thunder-

storm

FZ Freezing

(super-

cooled)DZ Drizzle

RA Rain

SN Snow

SG Snow

grains

PL Ice pellets

GR Hail

GS Small

hail and/

or snow

pellets

UP Unknown

precipi-

tationBR Mist

FG Fog

FU Smoke

VA Volcanic

ash

DU Wide-

spread

dust

SA Sand

HZ HazePO Dust/sand

whirls (dust

devils

SQ Squalls

FC Funnel

cloud(s)

(tornado or

waterspout)

SS Sandstorm

DS Duststorm

Once it has been decided there is a weather phenomenon to be reported, the

present weather is encoded by considering each column in the table above.

Example: There is rain: RA

It is heavy: +

It is a shower: SH

The encode becomes +SHRA .

If more than one weather phenomenon is observed, separate groups will be

encoded. However, for more than one form of precipitation, these forms of

precipitations will be combined in a single group with the dominant type of

precipitation being reported first.

Example: Moderate rain and snow with snow as the dominant precipitation

should be encoded as:

SNRA

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There are a few restrictions on the weather phenomena, the most significant

being:

– Intensity is reported only with precipitation (including showers and

thunderstorms with precipitation), duststorms or sandstorms.

– Smoke, haze, widespread dust and sand (except drifting sand) are reported

only when visibility has been reduced to 5 000 m or less.

– Mist is reported when visibility is reduced by water droplets to 1 000 to

5 000 m.

– Fog is reported when visibility is reduced by water droplets to less than

1 000 m.

– Hail ( GR) should be used only when the diameter of the largest hailstones

observed is 5 mm or more. GS shall be used in all other cases.

– VC denotes between 8 and 16 km of the aerodrome reference point.

Notes:

1. When visibility is 5 000 m or less, one of the phenomena FU, HZ, DU, SA and BR is

reported in the METAR/SPECI .

2. When visibility is above 5 km, the phenomena FU, HZ, DU, SA and BR are not present

by definition and are therefore not reported. For instance, if visibility is 5 000 m, it

will be encoded as 5000 together with the phenomena FU, HZ, DU, SA and BR ,

causing this reduction in visibility.

3. Whereas if visibility is 5 001 to 5 999 m this is still encoded as 5 000 (rounded down

to the nearest 1 000 m) in the METAR/SPECI , but the phenomena FU, HZ, DU, SA

and BR will not appear.

4. The qualifier TS shall be used whenever thunder is heard or lightning detected at

the aerodrome within the 10-min period preceding the observation.

5. The descriptor SH (showers) cannot be associated with ice pellets ( PL).

6. When an automatic observing system is used and when the type of precipitation

cannot be identified by this system, the abbreviation REUP shall be used for recent

unknown precipitation.

7. When an automatic observing system is used and when showers ( SH) cannot be

determined with a method that takes account of the presence of convective cloud,

the precipitation should not be characterized by SH.

CODE FORMAT

NsNsNshshshs

V Vhshshs

NSC

NCD

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW R24/P2000 +SHRA FEW005

FEW010CB SCT018 BKN025

6. CLOUD or VERTICAL VISIBILITY

Cloud groups consist of six characters under normal circumstances. The first

three indicate cloud amount with:

1/8 to 2/8 being reported as FEW (few)

3/8 to 4/8 being reported as SCT (scattered)

5/8 to 7/8 being reported as BKN (broken) and

8/8 being reported as OVC (overcast)

The last three characters indicate the height of the base of the cloud in units of

30 m (100 ft) up to 3 000 m (10 000 ft) and in steps of 300 m (1 000 ft) above.

Example: 3/8 of stratocumulus with a base of 1 850 ft will be encoded as:

SCT018

Note: The cloud base is rounded down, in this case to 1 800 ft.

Cloud type

Types of clouds other than significant convective clouds are not identified.

Significant convective clouds are:

– Cumulonimbus indicated by CB ;

– Cumulus congestus of great vertical extent indicated by TCU .

The contraction TCU , taken from “ Towering CUmulus”, is an ICAO abbreviation

used to describe this type of cloud.

Reported cloud groups

The cloud group can be repeated to report different layers or masses of cloud,

but the number of groups should not normally exceed three. The following

criteria should be followed when selecting the cloud layers to be reported:

– The lowest individual layer (mass) of any amount;

– The next individual layer of more than 2/8;

– The next higher layer of more than 4/8.

In addition : Significant convective clouds ( CB or TCU ) should be reported if

not already reported in one of the three groups above.

Example: If there were 1/8 stratus at 500 ft,

2/8 cumulonimbus at 1 000 ft,

3/8 cumulus at 1 800 ft,

5/8 stratocumulus at 2 500 ft,

the reported cloud would be:

FEW005 FEW010CB SCT018 BKN025

At mountain stations, when cloud base is below station level, the cloud group

should read NsNsNs///.

Example: SC T///, FEW///CB

Notes:

1. The cloud groups are reported in ascending order of height.

2. When there are no clouds below 1 500 m (5 000 ft) or below the highest minimum

sector altitude, whichever is greater, no restriction to vertical visibility and the

abbreviation CAVOK is not appropriate, the abbreviation NSC (Nil Significant Cloud)

is used.

3. When cumulonimbus ( CB) and T owering CUmulus ( TCU ) have a common cloud

base, the type of cloud is reported as CB and the amount of cloud is encoded as the

sum of CB and TCU amounts at that cloud base.

4. When an automatic observing system is used and the cloud type cannot be observed

by that system, the code type in each cloud group shall be replaced by /// . If no

clouds are detected by that system, the abbreviation NCD shall be used.

Vertical visibility

When the sky is obscured and cloud details cannot be assessed but information

on vertical visibility is available, the cloud group should be replaced by a five-

character group, the first two characters being V V followed by the vertical

visibility in units of 30 m or 100 ft, as for cloud base. When the sky is obscured

but the vertical visibility cannot be assessed, the group will read V V///.

Example: V V003 (vertical visibility 300 ft)

CAVOK

The code word CAVOK shall be used when the following conditions occur

simultaneously at the time of the observation:

(a) Visibility is 10 km or more;

(b) No cloud below 1 500 m (5 000 ft) or below the higher minimum sector

altitude, whichever is greater, and no CB;

(reproduced on page 13) of the Manual on Codes (WMO-No. 306),

Volume I.1, Part A – Alphanumeric codes, section C.

CODE FORMAT

T’T’/T’dT’d

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW R24/P2000 +SHRA FEW005

FEW010CB SCT018 BKN025 10/03

7. AIR AND DEWPOINT TEMPERATURE

The observed air temperature and dewpoint temperature, each as two figures

rounded to the nearest whole degree Celsius, should be reported as follows:

Temperatures below 0 °C will be preceded by M to indicate “minus”.

Example: –9.5 °C is reported as M09 .

Note: Air temperature and dewpoint values of 0.5° will be rounded up to the higher

whole degree.

Example: Air temperature: 9.5 °C

Dewpoint temperature: 3.3 °C

Will be reported as: 10/03

CODE FORMAT

QPHPHPHPH

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW R24/P2000 +SHRA FEW005

FEW010CB SCT018 BKN025 10/03 Q0995

8. PRESSURE – QNH

The last group of the main part of the report should indicate the QNH rounded

down to the nearest whole hectopascal. The group starts with the letter Q

followed by four figures.

Example: A QNH of 995.6 hPa is reported as:

Q0995

Note: In some countries, inches of mercury are used as the unit of QNH. In this case,

the indicator will be A (instead of Q ).

Example: A QNH of 30.05 in is reported as:

A3005

CODE FORMAT

WS R DRDR ( WTsTs/SS’)

REw’w’ or or (RDRDR/ERCReReRBRBR)

WS ALL RWY ( WTsTs/HHsHsHs)

ENCODE SO FAR

SPECI LUDO 211025Z 31015G27KT 280V350

4000 1400SW R24/P2000 +SHRA FEW005

FEW010CB SCT018 BKN025 10/03 Q0995

RERA WS R24 W19/S4 24451293

9. SUPPLEMENTARY INFORMATION

For international dissemination, this section is used to report:

– Recent weather phenomena of operational significance;

– Information on wind shear in the lower layers;

– Other information only in accordance with regional air navigation

agreements, including:

• Sea-surface temperature and the state of the sea or significant wave

height;

• State of the runway.

Recent weather

Using the indicator letters RE , information on recent weather shall be reported,

up to a maximum of three groups using the abbreviations given in section 5, if

the following weather phenomena were observed during the previous hour, or

since the last observation, but not at the time of observation. The time of

observation is taken to cover the previous 10 min.

– Freezing (FZ) precipitation

– Moderate or heavy precipitation (including showers – SH)

– Moderate or heavy ice pellets (PL), hail (GR), small hail and/or snow pellets

(GS)

– Blowing (BL) snow

– Sandstorm or duststorm (SS or DS)

– Thunderstorm (TS)

– Funnel cloud(s) (tornado or waterspout – FC)

– Volcanic ash (VA)

No intensity of significant recent weather phenomena shall be indicated.

Example: Heavy rain 20 min before the time of observation, with moderate

rain at the time of observation, is coded as:

RERA

Note: When an automatic observing system is used and when the type of precipitation

cannot be identified by this system, the abbreviation REUP shall be used for recent

unknown precipitation.

Wind shear

Where local circumstances so warrant, information on the existence of wind

shear significant to aircraft operations along the take-off or approach paths in

the lowest 500 m (1 600 ft) should be reported using the following groups, as

necessary:

WS R DRDR

WS ALL RWY

where DRDR is the runway designator.

WS R24 indicates that wind shear has been reported in either the take-off or

landing zones, or both, of runway 24.

Sea-surface temperature and the state of the sea or significant wave

height

Information on sea-surface temperature and the state of the sea or significant

wave height shall be given using the following group:

(WTsTs/SS’) or ( WTsTs/HHsHsHs)

where:

– W is a letter indicator for the temperature of the sea surface;

– TsTs is the sea-surface temperature coded or decoded as indicated in Part A,

section 7 (page 21);

– SS’ is the state of the sea as indicated in Code table 3700 where S is the

letter designator and S’ is the state of the water surface;

– HHsHsHs is the significant wave height where H is the letter indicator and

HsHsHsis the significant wave height in decimetres.

Example: Sea-surface temperature: 18.7 °C

State of the sea: Moderate

W19/S4

State of the runway

The runway state group is expected to be included in METAR and SPECI as

received from airport managers.

Information on the state of the runway shall be given using the following group:

(RDRDR/ERCReReRBRBR)

where:

– DRDR is the runway designator reported in accordance with the relevant

regional ICAO air navigation plan;

– ER is the runway deposit (Code table 0919);

– CR is the extent of the runway contaminated (Code table 0519);

– eReR is the depth of the deposit (Code table 1079);

– BRBR is the estimated surface friction (Code table 0366).

Example: 30 per cent of runway 24 is covered with dry snow with a depth

of 12 mm and leading to a medium braking action:

DRDR = 24

ER = 4

CR = 5

eReR = 12

BRBR = 93

24/451293

Note: The state of the runway shall not be included as supplementary information

in METAR and SPECI as of 3 November 2021.

COMPLETE CODE FORMAT

METAR

or COR CCCC YYGGgg Z NIL AUTO

SPECI

KT ordddff Gfmfm MPS dndndnVdxdxdx

V V V V

or VNVNVNVNDv RDRDR/VRVRVRVRi

CAVOK

NsNsNshshshs

V Vhshshs T’T’/T’dT’d QPHPHPHPH

w’w’ or

NSC

NCD

WS R DRDR ( WTsTs/SS’)

REw’w’ or or (RDRDR/ERCReReRBRBR)

WS ALL RWY ( WTsTs/HHsHsHs)

10. MISSING ELEMENTS

If a meteorological element in METAR or SPECI is temporarily missing, or its

value considered temporarily as incorrect, it is replaced by a solidus (/) for each

missing digit.

Examples: Surface wind: ///KT

270//K T

//////K T

Visibility: ////

Runway visual range: R24/////

Note: In this RVR example, four solidi (////) are appended to the “R24/” designator.

Present weather: //

Cloud: BKN//////

///018CB

//////CB

//////TCU

V V///

/////////

Note: In the first and last cloud examples, the cloud type (CB or TCU) that is missing

has been replaced by three solidi (///) at the end of the cloud group.

Air and dewpoint temperature: ///03

10///

/////

Note: In the first temperature example, two solidi (//) precede the “/03” dewpoint

temperature. In the second temperature example, two solidi (//) follow the “10/” air

temperature. In the third temperature example, air temperature and dewpoint

temperature are both missing (// and // either side of /).

Pressure – QNH: Q////

Supplementary information: RE//

W///S4

W17/H///

PART B

TREND FORECASTS

TREND forecasts are appended to a METAR or SPECI . The forecaster should

ensure that the encoding of the forecasts follows the agreed international

standard practices. The decoding of these forecasts is carried out by a variety

of people: pilots, air traffic services staff, operations personnel and meteorologists.

Consequently, this guidance is aimed at decoding. However, in order to

overcome any confusion, the encoder may find it useful to note how the user

interprets the forecast.

A first and very important point is that the information contained in the TREND

is a forecast covering a period of 2 h from the time of observation, and this

information is the forecaster’s best estimate of its likely occurrence. The

atmosphere is not homogeneous and sizeable variations in the visibility and

cloud base occur naturally. For instance:

– With visibilities of less than 1 000 m, changes of 30 per cent or more in a

period of 4 min occur on a significant number of occasions (5–10 per cent).

– With runway visual range in the range 360–1 100 m, changes at the rate

of 100 m/min can occur.

– Cloud base changes of 45 m (150 ft) in 1 min and/or over a horizontal

distance of 1.6 km occur on a significant number of occasions.

The forecast times of occurrence are also the forecaster’s best estimate.

Statistically, differences between forecast and actual times of 30 min will occur

on a significant number of occasions.

A TREND forecast consists of a concise statement of expected significant changes

in the meteorological conditions at the aerodrome to be appended to a routine

or special report ( METAR , SPECI ). The period of validity of a TREND forecast is

2 h from the time of the report, and this report forms an integral part of the

forecast. The TREND forecast indicates significant changes in respect of one or

more of the elements: surface wind, prevailing visibility, weather and cloud.

Only those elements for which a significant change is expected are included.

When no significant change is expected to occur, this is indicated by the

abbreviation NOSIG .

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Notes:

1. In the case of significant changes in respect of cloud, all cloud groups, including

layers or masses not expected to change, are indicated.

2. In the case of significant changes in visibility, the phenomenon causing the reduction

of visibility is indicated.

3. The units and scales used in TREND shall be the same as those used in the report

to which it is appended.

CODE FORMAT

(T T T T T

NOSIG )

Example: BECMG FM 1100

Decode: Becoming from 1100 UTC

ENCODE SO FAR

BECMG FM1100

1. CHANGE INDICATORS

When a significant change is expected in one or several of the observed elements

(surface wind, prevailing visibility, weather, clouds or vertical visibility), one of

the following change indicators is used for T T T T :

BECMG or TEMPO

The time group, GGgg , preceded without a space by one of the letter indicators

FM (from), TL (until) or AT (at) is used as appropriate.

Example: TEMPO FM1030

BECMG

The change indicator BECMG is used to describe expected changes which reach

or pass specified values at a regular or irregular rate. The period during which,

or the time at which, the change is forecast to occur is indicated using the

abbreviations FM , TL or AT , as appropriate.

(a) When a change is forecast both to begin and end within the TREND forecast

period, the beginning and end of change are indicated by using the

abbreviations FM and TL , respectively, with the associated time groups,

for example, for a TREND forecast period from 1000 to 1200 UTC in the

form:

BECMG FM1030 TL1130

(b) When the change is forecast to start at the beginning of the TREND period

but to be completed before the end of that period, only the abbreviation

TL and its associated time group is used to indicate the end of the change.

Example: The prevailing visibility at observation time is 6 km and is expected

to decrease, becoming 3 000 m in mist until 1100 UTC.

BECMG TL1100 3000 BR

and to be completed at the end of that period, the abbreviation FM and

its associated time group is used to indicate the beginning of the change.

For example:

BECMG FM1100

(d) When the change is forecast to occur at a specific time during the TREND

forecast period, the abbreviation AT followed by the associated time group

is used to indicate the time of the change. For example:

BECMG AT1100

(e) When the change is forecast to start at the beginning of the TREND forecast

period and to be completed by the end of that period, or when the change

is forecast to occur within the TREND period but the time is uncertain, the

abbreviations FM, TL or AT and their associated time groups are omitted

and the change indicator BECMG is used.

(f) When changes are forecast to take place at midnight UTC, the time is

indicated as follows:

(i) By 0000 when associated with FM and AT ;

(ii) By 2400 when associated with TL .

TEMPO

The change group TEMPO is used to describe forecast temporary fluctuations

in the meteorological conditions which reach or pass specified values and last

for a period of less than 1 h in each instance and in total for less than half of the

forecast period during which the fluctuations are forecast to occur. The period

during which the temporary fluctuations are expected to occur is indicated by

using the abbreviations FM and/or TL , as appropriate, followed by a time group.

(a) When the period of temporary fluctuations is forecast to begin and end

within the TREND forecast period, the beginning and end are indicated

by using the abbreviations FM and TL , respectively, with their associated

time groups, for example, for a TREND forecast period from 1000 to

1200 UTC, in the form:

TEMPO FM1030 TL1130

(b) When the period of temporary fluctuations is forecast to start at the

beginning of the TREND period but to finish before the end of that period,

only TL and its time group is used to indicate the end of the fluctuations.

For example:

TEMPO TL1130

TREND period and to continue throughout the remainder of the period,

the abbreviation FM and its associated time group only is used to indicate

the beginning of the fluctuations. For example:

TEMPO FM1030

(d) When the period of the temporary fluctuations is forecast to start at the

beginning of the TREND period and to continue throughout the remainder

of that period, the change indicator TEMPO is used alone.

NOSIG

When no significant changes are forecast to occur during the TREND forecast

period, the change indicator groups are omitted and the abbreviation NOSIG

is used instead.

Following the change indicator groups, only the group(s) referring to the

element(s) which is/are forecast to change significantly is/are included. However,

in the case of clouds, if a significant change is expected, all cloud groups

including any significant layer(s) or masses not expected to change are given.

Note: The indicator PROB shall not be used in TREND forecasts.

CODE FORMAT

dddff Gfmfm KT or

MPS

Example: 25035G50KT

Decode: Forecast surface wind 250° 35 kt with gusts to 50 kt

ENCODE SO FAR

BECMG FM1100 25035G50KT

2. SURFACE WIND

TREND indicates changes in the surface wind which involve either:

(a) A change in the mean wind direction of 60° or more, the mean speed before

and/or after the change being 10 kt (5 m s–1) or more;

(b) A change in the mean wind speed of 10 kt (5 m s–1) or more;

are established following consultation between the air traffic services

authority, the meteorological authority and the operators concerned.

Example: An expected increase in the wind speed to 35 kt with a maximum

gust of 50 kt sometime during the TREND period is indicated by:

BECMG 25035G50KT

CODE FORMAT

V V V V

CAVOK

Example: 6000

Decode: Forecast visibility 6 km

ENCODE SO FAR

BECMG FM1100 25035G50KT 6000

3. VISIBILITY

Change indicators are used when the prevailing visibility is expected:

(a) To improve and change to or pass through one or more of the following

values: 150, 350, 600, 800, 1 500 and 3 000 m;

(b) To deteriorate and pass through one or more of the following values: 150,

350, 600, 800, 1 500 and 3 000 m. Depending upon the number of lights

conducted in accordance with the visual flight rules, an additional value

of 5 000 m may be added to the list.

Example: Temporary reductions throughout the TREND forecast period of

the prevailing visibility to 740 m in fog is rounded down to 700 m

and indicated by:

TEMPO 0700

CODE FORMAT

w’w’

NSW

Example: NSW

Decode: No significant weather

ENCODE SO FAR

BECMG FM1100 25035G50KT 6000 NSW

4. WEATHER PHENOMENA

Significant forecast weather, using the abbreviations as indicated in Part A,

section 5 (page 13), is restricted to the onset, cessation or change in intensity

of the following weather phenomena:

– Freezing (FZ) precipitation;

– Freezing fog;

– Moderate or heavy precipitation (including showers – SH);

– Low drifting (DR) dust, sand or snow;

– Blowing (BL) dust, sand or snow;

– Duststorm (DS);

– Sandstorm (SS);

– Thunderstorm (TS);

– Squall (SQ);

– Funnel cloud (tornado or waterspout – FC);

– Other weather phenomena given in Code table 4678 (see page 13) which

are expected to cause a significant change in visibility.

To indicate the end of the occurrence of significant weather phenomena, the

abbreviation NSW (Nil Significant W eather) replaces the group w’w’ .

Example: For a TREND forecast period 0300 and 0500, a thunderstorm with

rain expected between 0300 and 0430 UTC is indicated by:

TEMPO TL0430 TSRA

The cessation of significant weather at 1630 UTC is indicated by:

BECMG AT1630 NSW

CODE FORMAT

NsNsNshshshs

V Vhshshs

NSC

ENCODE SO FAR

BECMG FM1100 25035G50KT 6000 NSW NSC

5. CLOUD or V ERTICAL VISIBILITY

Significant changes in cloud are indicated when one or more of the following

four conditions are expected:

(a) The height of the base of a cloud layer of BKN or OVC extent is below or

expected to fall below 450 m (1 500 ft) and is forecast to change to or pass

any one of the following values: 30, 60, 90, 150, 300 and 450 m (100, 200,

300, 500, 1 000 and 1 500 ft).

Example: A forecast of a lowering of the cloud base to 500 ft starting at the

beginning of the TREND period and ending by 1130 UTC is

indicated by:

BECMG TL1130 OVC005

(b) The height of the base of the cloud layer is below, or is expected to fall

below, 450 m (1 500 ft), and the cloud amount is forecast to change from:

SCT or FEW increasing to BKN or OVC

BKN or OVC decreasing to SCT or FEW

Example: A forecast of a rapid increase in stratus cloud at 1130 UTC from

SCT to OVC is indicated by:

BECMG AT1130 OVC010

observations are available, and the forecast indicates changes in vertical

visibility to, or passing, any one of the following values: 30, 60 or 150 m

(100, 200 or 500 ft).

(d) No significant change in the clouds is expected during the period of the

TREND , the cloud groups are not repeated and therefore no cloud details

are given.

To indicate a change to no cloud below 1 500 m (5 000 ft) or the highest minimum

sector altitude, whichever is the greater, and when no CB are forecast, and CAVOK

is not appropriate, the abbreviation NSC (Nil Significant Cloud) replaces the cloud

and vertical visibility groups.

Criteria for indicating changes in the TREND forecast, based on local aerodrome

operating minima, additional to those specified above, shall be used only when

these criteria have been agreed by the meteorological authority and the

operator(s) concerned.

COMPLETE CODE FORMAT

(T T T T T T TGGgg dddff Gfmfm KT

or or

NOSIG) MPS

NsNsNshshshs

V V V V w’w’ or

or or VVhshshs ( RMK... )

CAVOK NSW or

NSC

Complete example:

BECMG FM1100 25035G50KT 6000 NSW NSC

DECODE

Becoming after 1100 UTC, surface wind 250° 35 kt, gusts to 50 kt,

visibility 6 km, nil significant weather and nil significant cloud

PART C

AERODROME FORECASTS – TAFs

Aerodrome forecasts ( TAFs) are complete descriptions of the meteorological

elements expected at and over the aerodrome throughout the whole of the

forecast period, including any changes considered to be significant to aircraft

operations.

TAFs are prepared by professional staff who, using the latest available regulations,

ensure that internationally agreed practices are followed. The decoding of these

forecasts is carried out by people of various disciplines and many will not have

easy access to these regulations. Consequently, this guidance is aimed at

decoders, although it may also be of interest to encoders.

As with the TREND forecast, it should be appreciated that, owing to the variability

of meteorological elements in space and time and to limitations of forecasting

techniques and the definitions of some of the elements, the specific value of any

element given in the forecast should be understood to be the most probable value

that the element is likely to assume during the period of the forecast.

TAFs describe the forecast prevailing conditions at an aerodrome and cover a

period of not less than 6 h and not longer than 30 h. The period of validity of

TAFs produced by meteorological offices should be determined by regional air

navigation agreement. Routine TAF s valid for less than 12 h should be issued

every 3 h, and those valid for 12 h up to 30 h every 6 h.

Amendments are issued as and when necessary. It is assumed that a later TAF

automatically amends and updates the ones issued previously, and not more

than one TAF is valid at an aerodrome at any given time.

TAFs are issued separately from the METAR or SPECI and do not refer to any

specific report. However, the preparation, amendment and cancellation, as

necessary, of the TAF depend, among others, upon receipt of the METAR or

SPECI of that aerodrome.

Aerodrome forecasts contain specific information presented in a fixed order.

The information and order are as follows:

IDENTIFICATION GROUPS

SURFACE WIND

PREVAILING VISIBILITY

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WEATHER

CLOUD (or vertical visibility, if appropriate)

EXPECTED SIGNIFICANT CHANGES

Notes:

1. CAVOK is used to replace the visibility, weather and cloud groups when the following

three conditions are simultaneously met:

– Visibility is 10 km or more;

– There is no cloud below 1 500 m (5 000 ft) or below the highest minimum

sector altitude, whichever is greater, and no cumulonimbus;

– There are no significant weather phenomena (see Code table 4678 on page 13).

2. The forecast period of the TAF may be divided into two or more self-contained parts

by using the indicator FMYYGGgg , where FM is the abbreviation of “from” and

YYGGgg is the date and time in UTC. A complete description of the prevailing

conditions is given at the beginning of the forecast or the self-contained parts

designated FMYYGGgg . Forecast significant changes to these conditions are

indicated as necessary.

CODE FORMAT

TAF

TAF AMD CCCC YYGGgg Z NIL Y1Y1G1G1/Y2Y2G2G2 CNL

TAF COR

Example 1: TAF LUDO 130530Z 1307/1316

Decode: Aerodrome forecast for LUDO international airport, time of origin

0530 UTC on the 13th, forecast valid for the period 0700 to

1600 UTC on the 13th

Example 2: TAF AMD LUDO 161500Z 1606/1712 CNL

Decode: Amended TAF for LUDO international airport issued on the 16th

of the month at 1500 UTC cancelling the previously issued TAF

valid from 0600 UTC on the 16th to 1200 UTC on the 17th of the

month

1. IDENTIFICATION GROUPS

This section contains eight parts, as follows:

– The aerodrome forecast code name ( TAF) included at the beginning of an

individual aerodrome forecast and at the beginning of a bulletin consisting

of one or more aerodrome forecasts;

– The code word AMD if the TAF is amended;

– The code word COR if the TAF is corrected;

– The ICAO location indicator of the aerodrome to which the forecast refers;

– The date and time of issue of the forecast;

– The code word NIL if the TAF is missing;

– The period covered by the forecast;

– The code word CNL if the TAF is cancelled.

CODE FORMAT

dddff Gfmfm KT

MPS

Example: 31015KT

Decode: Forecast surface wind 310° at 15 kt

ENCODE SO FAR

TAF LUDO 130530Z 1307/1316 31015KT

2. SURFACE WIND

Normally this is a five-figure group followed by an abbreviation to indicate the

wind speed units used. The first three figures indicate the wind direction from

true north, and the last two the mean wind speed.

Example: 31015KT

Additionally, if the wind is expected to be gusty and the maximum gust speed

likely to exceed the mean speed by 10 kt (5 m s–1) or more, this gust must be

indicated using the letter G directly after the mean speed, followed by the gust

speed.

Example: 31015G27KT

The encode VRB is used only when the mean wind speed is less than 3 kt

(2 m s–1). VRB for higher wind speeds shall be used only when the variation of

wind direction is 180° or more, or when it is impossible to forecast a single wind

direction, for example during a thunderstorm.

When a wind speed of 100 kt or more is forecast, it should be indicated as P99KT .

Example: 310P99KT

CODE FORMAT

V V V V

CAVOK

Example: 8000

Decode: Visibility 8 km

ENCODE SO FAR

TAF LUDO 130530Z 1307/1316 31015KT 8000

3. VISIBILITY

Forecast prevailing visibility is encoded as a four-figure group. As with the

METAR code, the figures are the expected values in metres, except that 9999

indicates a prevailing visibility of 10 km or greater.

Example: A forecast prevailing visibility of 8 km is indicated as 8000.

When the prevailing visibility cannot be forecast, the lowest forecast visibility

shall be used.

CODE FORMAT

w’w’

NSW

Example: SHRA

Decode: Moderate rain shower

ENCODE SO FAR

TAF LUDO 130530Z 1307/1316 31015KT 8000 SHRA

4. WEATHER

Forecast weather, using the appropriate abbreviations given in Code table 4678

(see page 13), is restricted to the occurrence of one or more, up to a maximum

of three, of the following weather phenomena, together with their characteristics,

which are deemed significant to aircraft operations:

– Freezing (FZ) precipitation;

– Freezing fog;

– Moderate or heavy precipitation (including showers – SH);

– Low drifting (DR) dust, sand or snow;

– Blowing (BL) dust, sand or snow;

– Duststorm (DS);

– Sandstorm (SS);

– Thunderstorm (TS);

– Squall (SQ);

– Funnel cloud (tornado or waterspout – FC);

– Other weather phenomena given in Code table 4678 which are expected

to cause a significant change in visibility.

Example: SHRA (moderate rain shower)

If no significant weather, as defined above, is expected to occur, the group is

omitted. However, after a change group, if the weather ceases to be significant,

the weather group w’w’ is replaced by NSW (abbreviation for Nil Significant

Weather).

CODE FORMAT

NsNsNshshshs

V Vhshshs

NSC

Example: FEW005 FEW010CB SCT018 BKN025

Decode: 1/8 to 2/8 cloud with base 500 ft

1/8 to 2/8 cumulonimbus with base 1 000 ft

3/8 to 4/8 cloud with base 1 800 ft

5/8 to 7/8 cloud with base 2 500 ft

ENCODE SO FAR

TAF LUDO 130530Z 1307/1316 31015KT 8000

SHRA FEW005 FEW010CB SCT018 BKN025

5. CLOUD ( or VERTICAL VISIBILITY)

Cloud information is presented in the same format as in the METAR . The group

usually consists of six characters, the first three indicating the expected cloud

amount, using the following abbreviations:

FEW – Few – 1/8 to 2/8

SCT – Scattered – 3/8 to 4/8

BKN – Broken – 5/8 to 7/8

OVC – Overcast – 8/8

The last three figures indicate the expected height of the base of the cloud, in

units of 30 m (100 ft).

Only the cloud type cumulonimbus ( CB) is indicated.

Examples: 1. 4/8 stratus at 1 000 ft is coded as:

SCT010

2. 7/8 cumulonimbus at 1 000 ft is coded as:

BKN010CB

When the forecaster expects more than one layer or mass of cloud, additional

cloud groups are given in accordance with the following:

– The lowest individual layer of any amount;

– The next individual layer covering more than 2/8;

– The next individual layer covering more than 4/8, additionally;

– Cumulonimbus cloud ( CB) when forecast, if not already in one of the groups

above.

Normally, the number of groups will not exceed three, except that cumulonimbus

will always be included if forecast.

The cloud groups are in the order of lower to higher levels of cloud base.

Example: The forecast is for 1/8 stratus at 500 ft

2/8 cumulonimbus at 1 000 ft

3/8 cumulus at 1 800 ft

5/8 stratocumulus at 2 500 ft

which would be encoded as:

FEW005 FEW010CB SCT018 BKN025

When the sky is expected to be obscured and information on vertical visibility

is available, the cloud group is replaced by V V hshshs, where the last three figures

for hshshs indicate the vertical visibility in units of 30 m (100 ft).

In some regions cloud information is limited to cloud of operational significance.

This is considered to be cloud below 1 500 m (5 000 ft) or the highest minimum

sector altitude, whichever is the greater, and cumulonimbus, whenever forecast.

Therefore, when no cumulonimbus or clouds below 5 000 ft or below the highest

minimum sector altitude, whichever is the greater, are forecast and CAVOK is

not appropriate, NSC (Nil Significant C loud) is used.

Example: When the prevailing visibility is expected to be 8 km and

altocumulus and cirrus clouds are forecast above 10 000 ft, the

cloud group would be replaced by NSC . If the prevailing visibility

is expected to be 10 km or more with the same cloud conditions,

then CAVOK should be used.

6. EXPECTED SIGNIFICANT CHANGES

Changes in the prevailing meteorological conditions which are considered

significant, and which therefore need to be indicated in the aerodrome forecast

(and also the thresholds for deciding if the TAF should be amended), are as follows.

Surface wind

When the surface wind is forecast to change through operationally significant

values. These values vary from one aerodrome to another and are agreed upon

following discussions between the meteorological authority, the appropriate

air traffic services authority and operators.

Visibility

When the surface prevailing visibility is forecast to improve and change to, or

pass through, one or more of the following values, or when that visibility is

forecast to deteriorate and pass through one or more of the following values:

150, 350, 600, 800, 1 500 and 3 000 m

Depending upon the number of flights conducted in accordance with visual

flight rules, an additional value of 5 000 m may be added.

Weather

When any of the weather phenomena listed in Part C, section 4 (page 55), is forecast

to begin, end or change in intensity. If significant weather as indicated in the main

body of the TAF message is forecast to end, after the change group, the w’w’ group

is replaced by NSW , the abbreviation for N il Significant Weather.

Example: TAF LUDO 130530Z 1307/1316 31015KT 8000 RA SCT006

BKN012 BECMG 1312/1314 NSW SCT025

Cloud height

When the height of the base of the lowest layer or mass of cloud covering 5/8

or more ( BKN or OVC ) is forecast to lift and change to, or pass through, one or

more of the following values or to lower and pass through one or more of the

following values:

30, 60, 150 or 300 m (or 100, 200, 500 or 1 000 ft)

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Depending upon the number of flights conducted in accordance with visual

flight rules, an additional value of 450 m (1 500 ft) may be added.

Cloud amount

When the amount of a cloud layer or mass of cloud below 450 m (1 500 ft) is

forecast to change

– from SCT or FEW , increasing to BKN or OVC

– from BKN or OVC , decreasing to SCT or FEW .

When cumulonimbus clouds are expected to develop or dissipate.

When vertical visibility is forecast to improve and change to, or pass through,

one or more of the following values, or to deteriorate and pass through one or

more of the following values:

30, 60, 150 or 300 m (100, 200, 500 or 1 000 ft)

CAVOK

When conditions are forecast to change to CAVOK , or CAVOK conditions will

cease (conditions requiring CAVOK are found under Part A, section 6 (page

17)).

CODE FORMAT

TTTTT YYGG/YeYeGeGe

TTYYGGgg

Example: TEMPO 1311/1316 4000 +SHRA

Decode: Temporarily between 1100 and 1600 UTC visibility 4 000 m and

heavy rain showers

ENCODE SO FAR

TAF LUDO 130530Z 1307/1316 31015KT 8000

SHRA FEW005 FEW010CB SCT018 BKN025

TEMPO 1311/1316 4000 +SHRA

7. INDICATION OF SIGNIFICANT CHANGES

(a) When one set of prevailing weather conditions is expected to change

significantly and more or less completely to a different set of conditions,

the time indicator group FMYYGGgg (where FM is the abbreviation for

“f rom”, YY is the date and GGgg is the time in hours and minutes UTC) is

used to indicate the beginning of a self-contained part of the forecast. All

conditions given before this group are superseded by conditions indicated

after the group.

Example: TAF LUDO 130530Z 1307/1316 27015KT 6000 NSC

FM131215 27017KT 4000 BKN010

(b) The groups BECMG YYGG/YeYeGeGe indicate a regular or irregular change

to the forecast meteorological conditions expected at an unspecified time

within the period YYGG to YeYeGeGe. This period will normally not exceed

2 h but will never be more than 4 h.

The change indicator is followed by groups describing only the

meteorological elements which are forecast to change significantly.

However, in the case of significant changes in cloud, all the cloud groups

as set out in Part C, section 5 (page 57), including layers or masses not

expected to change, should be indicated.

Unless a further set of change groups is used, the conditions given after

BECMG YYGG/YeYeGeGe are expected to prevail from the date and time

YeYeGeGe to the end of the forecast period.

Example: TAF LUDO 130530Z 1307/1316 27015KT 6000 NSC

BECMG 1310/1312 4000 BKN010

Meaning

The forecast conditions start to change at 1000 UTC and the prevailing conditions

for the period 1200 to 1600 UTC are expected to be:

Surface wind: 270° at 15 kt

Visibility: 4 000 m

Weather: None significant to operations

Cloud: 5/8 to 7/8 with a base of 1 000 ft

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the forecast meteorological conditions which may occur at any time during

the period YYGG to YeYeGeGe. The meteorological conditions following

these groups are expected to last less than 1 h in each instance and in

aggregate less than half the period indicated by YYGG/YeYeGeGe.

CODE FORMAT

TTTTT YYGG/YeYeGeGe

PROB C2C2 YYGG/YeYeGeGe or

TTYYGGgg

Example: PROB30 TEMPO 1314/1316 TSRA SCT005 BKN010CB

Decode: Moderate probability temporarily on the 13th between 1400 and

1600 UTC of thunderstorm with moderate rain and 1/8 to 4/8

cloud at 500 ft and 5/8 to 7/8 cumulonimbus at 1 000 ft

ENCODE SO FAR

TAF LUDO 130530Z 1307/1316 31015KT 8000

SHRA FEW005 FEW010CB SCT018 BKN025

TEMPO 1311/1416 4000 +SHRA PROB30

TEMPO 1314/1316 TSRA SCT005 BKN010CB

Note: If a temporary fluctuation persists longer than 1 h or in aggregate more than

half the forecast period, these conditions would be the predominant ones and the change

indicator BECMG should be used.

(d) When the confidence in forecasting alternative values is not high, yet the

forecast element being considered is significant to aircraft operations, the

groups PROBC2C2 YYGG/YeYeGeGe are used. C2C2 indicates the percentage

probability of occurrence, with only the values 30 or 40 per cent being

used. The PROB group is always followed by a time group YYGG/YeYeGeGe

(example 1) or a change group and a time group TTTTT YYGG/YeYeGeGe

(example 2).

Example 1:

TAF LUDO 132030Z 1322/1407 27003KT 4000 SCT008 BECMG

1403/1405 1500 BR BKN004 PROB30 1405/1407 0800 FG

This indicates that the visibility will fall to 1 500 m by 0500 UTC on the 14th

with a moderate probability of fog with a visibility of 800 m between 0500

and 0700 UTC on the same day (14th).

Example 2:

TAF LUDO 130530Z 1307/1316 27015KT 9999 SCT015 TEMPO

1311/1316 4000 +SHRA BKN010CB PROB30 TEMPO 1314/1316 TSRA

This indicates that, on the 13th, heavy showers of rain are likely after

1100 UTC with a moderate probability of a thunderstorm with moderate

rain after 1400 UTC.

Note: It is assumed that, if the probability of an occurrence is 50 per cent or greater,

confidence is high and the alternative values are indicated using BECMG, TEMPO or FM,

as appropriate. When the probability of occurrence is less than 30 per cent, it is not

considered significant from an operational point of view and the associated phenomena

are therefore not mentioned.

TEMPO , which means that the fluctuations will occur for less than half of the

time, should not be confused with a probability of 30 or 40 per cent. With

TEMPO , the forecaster is confident that the temporary fluctuations will take

place; with PROB30 there is only a moderate probability that they will occur.

(e) The number of change and probability groups should be kept to a minimum

and should not normally exceed five groups.

Amendments

When an aerodrome forecast TAF requires amendment in accordance with

Part C, section 6 (page 59), the amended forecast is indicated by inserting AMD

after TAF in the identifier, and this new forecast covers the remaining validity

period of the original TAF .

Example: TAF AMD LUDO 130820Z 1308/1316 . . .

Note: The time of issue of this TAF AMD is 0820 UTC but the forecast is valid from

0800 to 1600 UTC.

Regional code forms:

Forecast maximum (TXTFTF/YFYFGFGFZ TN TFTF/YFYFGFGFZ)

and minimum

temperatures

This group is used only if agreed regionally and is included here for the sake of

completeness. A full description of this code can be found in the Manual on Codes

(WMO-No. 306).

Only meteorological offices determined by regional air navigation agreement

shall issue 30-h TAF s.

COMPLETE CODE FORMAT

TAF

or NIL KT

TAF AMD CCCC YYGGgg Z or dddff Gfmfm or

or Y1Y1G1G1/Y2Y2G2G2 or MPS

TAF COR CNL

NsNsNshshshs

V V V V w’w’ or VVhshshs

or or NSC

CAVOK

(TXTFTF/YFYFGFGF Z TN TFTF/YFYFGFGFZ)

PROB C2C2 or

PROB C2C2 T T T T T YYGG/YeYeGeGe KT V V V V

or TTTTT dddff Gfmfm or

or MPS or

T TYYGGgg

CAVOK

w’w’ NsNsNshshshs

or or VVhshshs

NSW or NSC

Complete example:

TAF LUDO 130530Z 1307/1316 31015KT 8000 SHRA FEW005

FEW010CB SCT018 BKN025 TEMPO 1311/1316 4000 +SHRA

PROB30 TEMPO 1314/1316 TSRA SCT005 BKN010CB

DECODE

Aerodrome forecast for LUDO international airport, time of origin

0530 UTC on the 13th, valid for the period 0700 on the 13th to

1600 UTC on the 13th. Surface wind 310° 15 kt, visibility 8 km,

moderate rain shower, cloud 1/8 to 2/8 base 500 ft, 1/8 to 2/8

cumulonimbus base 1 000 ft, 3/8 to 4/8 base 1 800 ft, 5/8 to 7/8 base

2 500 ft. Temporarily between 1100 and 1600 UTC same day, visibility

4 000 m in heavy rain showers, with a moderate probability temporarily

between 1400 and 1600 UTC of a thunderstorm with moderate rain,

cloud 3/8 to 4/8 base 500 ft and 5/8 to 7/8 cumulonimbus base 1 000 ft

EXPLANATION OF WEATHER PHENOMENA

SIGNIFICANT TO AVIATION

1. Drizzle (DZ)

Fairly uniform precipitation in very fine drops of water with a diameter of less

than 0.5 mm. The impact of drizzle droplets falling on a water surface is

imperceptible, but continuous drizzle may produce a runoff from roofs and

runway surfaces. The drops can only reach the ground without evaporating if

they fall from very low clouds. Generally, the heavier the drizzle, the lower the

cloud base. Visibility is inversely related to both the intensity of precipitation

and the number of droplets. Light drizzle corresponds to negligible runoff from

roofs; heavy drizzle to a rate of accumulation greater than 1 mm/h.

2. Rain (RA)

Precipitation of liquid water droplets of appreciable size (greater than 0.5 mm).

Raindrops form in quite deep clouds where there is vertical motion capable of

supporting sizeable water droplets. The heavier the rain, the deeper the clouds

producing it. Intermittent rain of moderate or heavy intensity indicates that cells

with locally strong updraughts are present.

3. Snow (SN)

Solid precipitation of single or agglomerated ice crystals falling from a cloud.

At very low temperatures, snowflakes are small and their structure simple. At

temperatures close to freezing point, the individual flakes may be composed of

a large number of ice crystals (predominantly star-shaped) and the flakes may

have a diameter greater than 25 mm.

4. Snow grains (SG)

The frozen equivalent of drizzle. They are very small and opaque white particles

of ice which fall from stratiform clouds. These particles are fairly flat or elongated

and their diameter is generally less than 1 mm.

5. Ice pellets (PL)

Transparent or translucent ice particles that cannot be crushed easily and have

a diameter of 5 mm or less. They are formed from freezing raindrops or largely

melted snowflakes which can indicate that at higher levels freezing rain may be

present, with the danger of severe icing after take-off or during descent/ landing.

Ice pellets may occur before or after freezing rain.

6. Hail (GR)

Transparent or partly or completely opaque pieces of ice (hailstones) with a

diameter generally between 5 mm and 50 mm. Very large stones weighing 1 kg

or more have been observed.

7. Small hail and/or snow pellets (GS)

The abbreviation GS is used to report two different types of precipitation:

(a) Small hail

Translucent ice particles with a diameter up to 5 mm which, when falling

on hard ground, bounce with an audible sound. Small hail consists of snow

pellets totally or partially encased in a layer of ice and is an intermediate

stage between snow pellets and hailstones.

(b) Snow pellets

White, opaque and approximately round ice particles, often falling together

with snow at a temperature near 0 °C. Snow pellets normally have a

diameter of 2 mm to 5 mm, are crisp and easily crushed and rebound when

falling on a hard surface.

8. Mist (BR)

The suspension of microscopic water droplets or wet hygroscopic particles in

the air, reducing horizontal visibility to 1 000 to 5 000 m. The relative humidity

is greater than 95 per cent.

Note: [concerning 7 and 8] Large cumulonimbus clouds are the main “factories”

where hail is produced in the atmosphere. Great cloud depth and extremely vigorous

updraughts within the cloud are necessary to support these pieces of ice long enough

for them to grow. Some of the hail is blown out of the side or top of the cloud before it

has completely formed, leading to reports of snow pellets.

9. Fog (FG)

The suspension in the air of very small water droplets, which reduces horizontal

visibility to less than 1 000 m.

10. Smoke (FU)

The suspension in the air of small particles produced by combustion, which

reduces horizontal visibility to 5 000 m or less. It should be noted that smoke

may be reported with a horizontal visibility of less than 1 000 m, if there are no

suspended water droplets and the relative humidity is not greater than about

90 per cent.

11. Volcanic ash (VA)

Atmospheric dust or particles varying considerably in size, originating from

active volcanoes. The small particles often penetrate the stratosphere and remain

suspended for a long period. Larger particles remain within the troposphere

and can be carried by the wind to different regions of the Earth. Scavenging by

rainfall and gravity eventually leads to the removal of volcanic ash from the

atmosphere. Larger particles, or a concentration of smaller ones, can considerably

damage aircraft, including their engines.

12. Widespread dust (DU)

The reduction of horizontal visibility to 5 000 m or less caused by the suspension

in the air of small particles of dust raised from the ground.

13. Sand (SA)

The reduction of horizontal visibility to 5 000 m or less caused by the suspension

in the air of small particles of sand raised from the ground.

14. Haze (HZ)

The suspension in the air of extremely small dry particles invisible to the naked

eye and sufficiently numerous to give the air an opalescent appearance with a

reduction in horizontal visibility to 5 000 m or less.

15. Dust/sand whirls (dust devils) (PO)

A rapidly rotating column of air over a dry and dusty or sandy ground carrying

dust and other light material picked up from the ground. Dust or sand whirls

are of a few metres in diameter. Normally in the vertical, they extend no higher

than 200 to 300 ft, but in very hot desert regions they may reach 2 000 ft.

16. Squall (SQ)

A strong wind that rises suddenly, generally lasting for at least 1 min. It is

distinguished from a gust by its longer duration. The sudden increase in wind

speed is at least 16 kt (8 m s–1), the speed rising to 22 kt (11 m s–1) or more and

lasting at least 1 min. Squalls are often associated with large cumulonimbus

clouds and violent convective activity, extending some kilometres horizontally

and several thousands of feet vertically.

17. Funnel cloud(s) (tornado or waterspout) (FC)

A phenomenon consisting of an often violent whirlwind, indicated by the

presence of a cloud column or funnel-shaped cloud, extending downwards

from the base of cumulonimbus cloud but not necessarily reaching the ground.

The diameter can vary from a few metres to some hundreds of metres. A well-

developed funnel cloud is called a tornado if over land and a waterspout if over

water. The most violent tornado can have associated wind speeds of up to about

300 kt (150 m s–1).

18. Sandstorm (SS)

An ensemble of particles of sand energetically lifted by a strong and turbulent

wind. The forward portion of the sandstorm may have the appearance of a wide

and high wall. The height to which sand is raised will increase with increasing

wind speed and instability.

19. Duststorm (DS)

Particles of dust energetically lifted by a strong and turbulent wind. Dust storms

are usually associated with hot, dry and windy conditions, especially just ahead

of vigorous cold fronts that can be cloud free. Dust particles typically have a

diameter of less than 0.08 mm and consequently can be lifted to far greater

heights than sand.

20. Shallow (MI)

This descriptor is used only with FG (fog) when the observed horizontal visibility

is 1 000 m or more, but, when between the ground and 2 m above the ground

(the assumed eye level of the observer), there is a layer in which the apparent

visibility is less than 1 000 m. Operationally, MIFG may cause problems because

runway markings and lights may be concealed.

21. Patches (BC)

This descriptor is used only with fog (FG) and indicates that there are fog patches

randomly covering the aerodrome. Hence, although the horizontal visibility as

reported in the METAR/SPECI is 1 000 m or more, the observer can see areas

where the apparent visibility is less than 1 000 m.

22. Partial (covering part of the aerodrome) (PR)

This descriptor is used only with fog (FG) and indicates that a substantial part

of the aerodrome is covered by fog, while the remainder is clear.

23. Low drifting (DR)

This descriptor indicates that dust, sand or snow has been raised by the wind to a

height of less than 2 m (the assumed eye level of the observer).

24. Blowing (BL)

This indicates that dust, sand or snow has been raised by the wind to a height

greater than 2 m and that consequently horizontal visibility has been reduced.

25. Shower(s) (SH)

Precipitation, often short-lived and heavy, falling from convective clouds. A

shower is characterized by the suddenness with which it starts and stops, and

generally by large and rapid changes in precipitation intensity.

26. Thunderstorm (TS)

One or more sudden electrical discharges, manifested by a flash of light

(lightning) and a sharp or rumbling sound (thunder). Thunderstorms are

associated with convective clouds (cumulonimbus) and are usually accompanied

by precipitation. The associated cumulonimbus has vertical updraughts that

may reach 30 m s–1 in the more vigorous cells. Downdraughts also occur,

especially in the later stages of development, with speeds of about half of those

for updraughts.

27. Freezing (supercooled) (FZ)

This descriptor is used only with fog (FG), drizzle (DZ) or rain (RA) when the

waterdrop temperature is below 0 °C (supercooled). On impact with the ground

or an aircraft, the drops of supercooled water form a mixture of water and clear

ice. Freezing fog normally deposits rime, rarely clear ice.

28. Precipitation intensity criteria

(a) Drizzle Light: rate < 0.1 mm h–1

Moderate: 0.1 ≤ rate < 0.5 mm h–1

Heavy: rate ≥ 0.5 mm h–1

(b) Rain Light: rate < 2.5 mm h–1

(including Moderate: 2.5 ≤ rate < 10.0 mm h–1

showers) Heavy: rate ≥ 10.0 mm h–1

(including Moderate: 1.0 ≤ rate < 5.0 mm h–1 (water equivalent)

showers) Heavy: rate ≥ 5.0 mm h–1 (water equivalent)

Note: Great care must be taken when interpreting observations of light snow without

understanding the potential hazard to aircraft operations. The accumulation of snow on

aircraft prior to take-off represents a significant safety hazard because of possible loss of

lift and increasing drag during take-off. The accumulation of as little as 0.8 mm of snow

or ice on the upper wing surface can result in a loss of lift and therefore endanger flight

safety.

Replaced when

automatic system is

used and no clouddetected by:COR CCCC YYGGgg

Z dddﬀGf mfm VVVV RDRDR/VRVRVRVRi w'w' N sNsNshshshs (cc)Ceiling And Visibility OK. Replaces visibility RVR, present weather and cloud if: (1) Visibility is 10 km or more; (2) No cumulonimbus cloud and no cloud

below 1 500 m (5 000 ft) or below the highest minimum sector altitude, whichever is greater; and (3) No signiﬁcant present weather (see table w'w')

Cloud type — only CB (cumulonimbus) or TCU (Towering CUmulus) indicated

or /// if it cannot be observed by automatic system

FEW – FEW (1–2 oktas)

Cloud amount: SCT – SC aTtered (3–4 oktas)

BKN – B roKeN (5–7 oktas)

OVC – OV erCast (8 oktas)Height of base of clouds in units of 30 m (100 ft)

Present weather (see table w'w')

RVR tendency indicator over past 10 min. U = upward; D = downward;

N = no distinct change. Omitted if impossible to determine

RVR (10-min mean) at the touchdown zone P2000 = more

than 2 000 m, M0050 = less than 50 m

Runway designator – for parallel runways may have

LL, L, C, R or RR appended ( L = left; C=centre; R = right)

Indicator of RVR

Prevailing visibility in metres or lowest visibility if visibility is not thesame and ﬂuctuating and the prevailing visibility cannot be determined

9999 = 10 km or more

Wind speed units used

Indicator of

Gust – if necessaryMaximum wind speed (gust) – if necessary

Mean wind speed (10-min mean or since discontinuity)

Mean wind direction in degrees true rounded oﬀ

to nearest 10° ( VRB = VaRiaBle when ﬀ < 3 kt)

In individual messages, day of the month and time of observation in hours andminutes UTCFully automated observation indicator

COR – Code word used as appropriateIndicator of UTC

METAR – Aviation routine weather report code name

SPECI – Aviation special weather report code nameMETAR

SPECIKT or

MPSsee Table: Aerodrome Forecast –

TAF decode for deﬁnitionsA E R O D R O M E W E A T H E R R E P O R T – M E T A R A N D S P E C I D E C O D E

IDENTIFICATION GROUPS SURFACE WINDRUNWAY VISUAL

RANGE (RVR)

WHERE REQUIRED,

UP TO FOUR

ACTIVE RUNWAYSCLOUDSaTREND FORECAST

TWO HOURS FROM TIME OF OBSERVATION

TTGGgg VVVV w’w’ N sNsNshshshs (cc) dddﬀGf mfmTTTTT

NOSIGWIND

SHEARSTATE OF

THE RUNWAYb

Runway designator – for parallel runwaysmay have

LL, L, C, R or RR appended

(L = left; C = centre; R = right)

Indicator of REcent weatherREcent weather since previous report (intensity NOT to be reported)RUNWAY

Wind Shear

Indicator of QNH in hectopascals. If Q = A then QNH is in inchesQNH rounded down to the whole nearest hectopascal or to tenths and hundredths of an inch, depending on indicator

Dewpoint temperature in whole degrees Celsius(if below 0 °C preceded by

Temperature in whole degrees Celsius(if below 0 °C preceded by

M) T'T'/T' dT'd QPHPHPHPH REw’w’ WS R DRDR ( WTsTs/SS’) ( WTsTs/HHsHsHs) (D RDR/ERCReReRBRBR) FORECAST

WIND

CHANGE

INDICATORS

CHANGE

AND

TIMEFORECAST CLOUDS

OF OPERATIONAL

SIGNIFICANCE OR

VERTICAL VISIBILITY

Replaced

whensigniﬁcantweatherendsby:

NSW

Nil

Signiﬁcant

Weather

Notes:

1.The w'w' groups are constructed by considering columns 1 to 5 in the table above in sequence, that

is, intensity, followed by description, followed by weather phenomena. An example could be: +SHRA

(heavy shower(s) of rain).

2.A precipitation combination has dominant type ﬁrst.

3.DR (low drifting) less than 2 m above the ground, BL (blowing) 2 m or more above the ground.

4.GR is used when hailstone diameter is 5 mm or more. When less than 5 mm, GS is used.

5.BR – visibility at least 1 000 m but not more than 5 000 m. FG – visibility less than 1 000 m.

6.VC – between 8 and 16 km of the aerodrome reference point.INTENSITY OR

PROXIMITYDESCRIPTOR OTHER PRECIPITATION OBSCURATIONWEATHER PHENOMENA QUALIFIERw'w' – SIGNIFICANT PRESENT, FORECAST AND RECENT WEATHERRECENT

WEATHERSUPPLEMENTARY INFORMATION

PRESENT

WEATHERPRESSURE

CAVOKPREVAILINGVISIBILITYFORECAST

WEATHER

FORECAST

VISIBILITYTEMP .

AND

DEW-

POINT

00000 = calm

AUTO

NIL – Code word used as appropriateNIL

Replaced

when all

runways areaﬀected by wind shear by:

WS ALL RWYRMK

NSC

Nil Signiﬁcant Cloud

dndndnVdxdxdx V nVnVnVn NDV RDRDR /VRVRVRVRi VVhshshsReplaced when

there are signiﬁcantvariations in RVR bythe group below:Followed when

visibility is not thesame and minimumvisibility ≠ prevailing and visibility < 1 500 mor visibility < 50% ofprevailing by thegroup below:P99 KT (P49 MPS)mean ﬀ orf

mfm = 100 KT

(50 MPS) or more

Followed when

there is a variationin wind directionof 60° or more butless than 180° andwind speed ≥ 3 KTby group below:Replaced when sky

is obscured andinformation on verticalvisibility is available bythe group below:

RVR tendency indicator

Indicator of RVRRVR in metres (1-min mean minimum value

during last 10 min)

Runway designator – for parallel runways may

have LL, L, C, R or RR

Indicator of VariabilityLowest visibility

Other extreme direction of wind(measured clockwise)

Extreme direction of windAbbreviation for

no directionalvariationsVertical visibility

in units of 30 m(100 ft) /// =vertical visibilityunavailable

Indicator of

Vertical Visibility00000 = calm

Followed by

VnVnVnVnDv

NSC

NCDReplaced when there

are no such clouds, norestriction on verticalvisibility and

CAVOK is

not appropriate by:

Nil Signiﬁcant Cloud

No Cloud Detected April 2019

a Clouds of operational signiﬁcance (i.e. below 1 500 m (5 000 ft) or below the highest minimum sector altitude, whichever is greater, and CB or TCU).

b State of the runway to be provided by appropriate airport authority.KT or

MPS

Indicatorof

Vertical

VisibilityVerticalvisibility inunits of30 m (100 ft)Information included by national decision but not disseminated internationally

Cloud type –

only CB

Forecast cloudamountForecast height

of base of cloud

Forecast signiﬁcant

weather (see table)

Forecast prevailing

visibility in metres 9999 = 10 km or more

Wind speed units

Forecast maximum wind speed (gust)

Signiﬁcant wave height, in decimetres

H indicator of the signiﬁcant wave height

Group indicator letterTemperature in whole degrees CelsiusIndicator of

Gust

Forecast mean wind speed

Forecast mean wind direction in degrees

true, rounded to nearest 10°(

VRB = V aRiaBle)

Associated time group in hours and minutes UTC

S' state of the water surface (see code S')

S indicator of state of the sea

Temperature in whole degrees Celsius

Group indicator letterFriction coeﬃcient/braking action

Depth of deposit

Extent of runway contamination

Indicator of runwayRunway depositsCan be AT or FM = F romM or TL = T ilL

BECMG = BEC oMinG or

TEMPO = TEMPO rary

NOSIG = NO SIG niﬁcant change

Lowest visibilityGeneral direction of lowest

visibility or most operationally signiﬁcant if minimum visibility observed in more than one direction

Note:

25 m STEP if RVR < 400 m

50 m STEP if 400 ≤ RVR < 800 m100 m STEP if RVR ≥ 800 m

ICAO four-letter location indicator

Replaced when skyexpected to beobscured andvertical visibilityforecasts areundertaken by:

Replaced when no CB

and no cloud below1 500 m (5 000 ft) orhighest minimumsector altitude,whichever is greater,are forecast and

CAVOK is not

appropriate by:VVhshshs

S' STATE OF THE SEA

Descriptiveterms

Calm (glassy)

Calm (rippled)Smooth (wavelets)SlightModerateRoughVery roughHighVery highPhenomenalCode

ﬁgure

– Light

Moderate

(no qualiﬁer)

+ Heavy or well-developed inthe caseof

PO and FC

VC In the vicinityMI Shallow

BC PatchesPR Partial

(covering part of

the aerodrome)

DR Low driftingBL BlowingSH Shower(s)TS ThunderstormFZ Freezing

(supercooled)DZ DrizzleRA RainSN SnowSG Snow grainsPL Ice pelletsGR HailGS Small hail

and/or

snow pellets

UP Unknown

precipitationBR Mist

FG FogFU SmokeVA Volcanic ash

DU Widespread

dust

SA SandHZ HazePO Dust/sand

whirls (dust

devils)

SQ Squalls

FC Funnel

cloud(s)

(tornado or waterspout)

SS Sandstorm

DS DuststormSEA-SURFACE TEMPERATURE

STATE OF ORSIGNIFICANT

THE SEA WAVE HEIGHT

1 2 5 3 4Abbreviated decode of METAR and SPECI

For details of codes, see

Manual on Codes,

(WMO–No. 306).

Replaced when sky

is expected to be

obscured and

information on vertical

visibility is available by:

VVhshshsVertical visibility in

units of 30 m (100 ft)

Indicator of

Vertical VisibilityReplaced when

signiﬁcant

weather pheno-

menon forecast

to end by:

NSW

Replaced when no CB and no cloud below

1 500 m (5 000 ft) or below the highest

minimum sector altitude, whichever is

greater, is forecast and CAVOK is

not appropriate by:

NSC

Nil Signiﬁcant Cloud

Nil Signiﬁcant

WeatherFORECAST CLOUD

AMOUNT

AND HEIGHTa FORECAST

SURFACE WINDIDENTIFICATION GROUPS

Probability is used to indicate the

probability of occurence of:

(a) an alternative element or

elements

(b) temporary ﬂuctuationsPROBABILITY DATE AND TIME CHANGE DATE AND TIME

PROB C2C2 YYGG/Y eYeGeGe TTTTT YYGG/Y eYeGeGeSIGNIFICANT CHANGES IN FORECAST

CONDITIONS INDICATED BY: BY REGIONAL

AGREEMENT

FORECAST

TEMPERATUREA E R O D R O M E F O R E C A S T – T A F D E C O D ECeiling And Visibility OK. Replaces visibility, weather and cloud if:

(1) Visibility is forecast to be 10 km or more

(2) No cumulonimbus cloud and no other cloud forecast below 1 500 m (5 000 ft)

or below the highest minimum sector altitude, whichever is greater, and

(3) No signiﬁcant weather forecast (see Table: Aerodrome Weather Report –

METAR and SPECI decode)

Cloud type — only CB (cumulonimbus) is indicatedTX, TN Indicators of maximum and minimum forecast temperatures, respectivelyYYTFTF Date and forecast temperatures at GFGF

Temperatures below 0 °C preceded by MYeYeGFGF Date and time UTC to which forecast temperature refersZ Indicator of UTC

PROB abilityOnly 30 or 40 used, indicating

30% or 40%Beginning day and time (UTC) YYGG

and end day and time (UTC)

YeYeGeGe of forecast periodTEMPO – TEMPO rary ﬂuctuations of less than one hour

and in aggregate less than half the period

indicated by YYGG/YeYeGeGeType of signiﬁcant changes:

BECMG – BEC oMinG, used where changes are expected

to reach or pass through speciﬁed values at

a regular or irregular rateBeginning day and time (UTC) YYGG and end day and

time (UTC) YeYeGeGe of forecast periodCCCC YYGGgg Z NIL Y1Y1G1G1/Y2Y2G2G2 CNL dddﬀGf mfm VVVV w'w' N sNsNshshshs (cc)KT or

MPSTAF or

TAF AMD or

TAF CORFORECAST

SIGNIFICANT

WEATHER

FORECAST

PREVAILING

VISIBILITYAbbreviated decode of TAF

For details of codes, see

Manual on Codes,

(WMO–No. 306).00000 = calm

P99 KT

(P49 MPS)

mean

fmfm =

100 KT

(50 MPS)

or more(TXYYT FTF /YeYeGFGFZ

TNYYT FTF /YeYeGFGFZ)

a Clouds of operational signiﬁcance (i.e. below 1 500 m (5 000 ft) or below highest minimum

sector altitude, whichever is greater, and CB or TCU).

Note: Meteorological oﬃces to issue 30-h TAFs are determined by regional air navigation agreement.April 2019OR

If one set of weather conditions is expected to change more or less completely

to a diﬀerent set of conditions, thus indicating the beginning of another

self-contained part of the forecast, by:

TTYYGGgg

This takes the form FMYYGGgg where FM is the abbreviation for FroM and

YYGGgg is the time in hours and minutes UTC. All forecast conditions before this

group are superseded by conditions indicated after the group.

Height of base of cloud in units of 30 m (100 ft)

FEW – FEW (1–2 oktas)

Cloud amount: SCT – SC aTtered (3–4 oktas)

BKN – B roKeN (5–7 oktas)

OVC – OV erCast (8 oktas)

Prevailing visibility in metres

9999 = 10 km or moreForecast signiﬁcant weather

(see table w'w' for METAR/SPECI decode)

Mean wind direction in degrees true rounded

to nearest 10° ( VRB = VaRiaBle when ﬀ < 3 kt)

Period of validity, beginning on Y1Y1 day of month at G1G1

(UTC) and ending on Y2Y2 day of month at G2G2 (UTC)

Code names for aerodrome forecast,

amended aerodrome forecast and

corrected aerodrome forecast, respectivelyICAO four-letter location indicatorDate and time of issue of forecast in UTCIndicator of UTCIndicator of cancelled forecast

Indicator of missing forecastMean wind speedIndicator of GustMaximum wind speed (gust)Wind speed units usedCAVOK

WMO-No. 782WMO-No. 782For more information, please contact:

World Meteorological Organization

7 bis , avenue de la Paix – P.O. Box 2300 – CH 1211 Geneva 2 – Switzerland

Strategic Communications Office

Tel.: +41 (0) 22 730 87 40/83 14 – Fax: +41 (0) 22 730 80 27

Email: communications@wmo.int

public.wmo.int

Aerodrome Reports and Forecasts – A Users’ Handbook to the CodesAerodrome

Reports

and Forecasts

A Users’ Handbook to the CodesJN 20644

WEATHER CLIMATE WATER

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