AMOSSG/5-SN No. 3

Appendix

APPENDIX

NOTES ON THE PRESENTATION OF THE PROPOSED AMENDMENT TO ANNEX 3

The text of the proposed amendment is arranged to show deleted text with a line through it and new text highlighted with grey shading as shown below:

1.	text to be deleted
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PROPOSED AMENDMENT TO

INTERNATIONAL STANDARDS

AND RECOMMENDED PRACTICES

METEOROLOGICAL SERVICE

FOR INTERNATIONAL AIR NAVIGATION

ANNEX 3

TO THE CONVENTION OF INTERNATIONAL CIVIL AVIATION

FIFTEENTH EDITION — JULY 2004

PART I — Core SARPs

. . .

CHAPTER 6. FORECASTS

Note.— Technical specifications and detailed criteria related to this chapter are given in Appendix 5.

. . .

6.2 Aerodrome forecasts

. . .

6.2.6 Recommendation.— The period of validity of a routine TAF should be not less than 9 hours nor more than 30 hours; this period should be determined by regional air navigation agreement. Routine TAF valid for less than 12 hours should be issued every 3 hours and those valid for 12 to 30 hours should be issued every 6 hours.

. . .

6.3 Landing forecasts

6.3.1 A landing forecast shall be prepared by the meteorological office designated by the meteorological authority concerned as determined by regional air navigation agreement; such forecasts are intended to meet requirements of local users and of aircraft within about one hour's flying time from the aerodrome.

6.3.2 Landing forecasts shall be prepared in the form of a trend forecast .

. . .

PART II

APPENDICES AND ATTACHMENTS

. . .

APPENDIX 3. TECHNICAL SPECIFICATIONS

RELATED TO METEOROLOGICAL OBSERVATIONS AND REPORTS

(See Chapter 4 of this Annex)

. . .

2. GENERAL CRITERIA RELATED TO

METEOROLOGICAL REPORTS

. . .

2.3 Criteria for issuance of local special reports

and SPECI

. . .

2.3.2 Recommendation.— SPECI should be issued whenever changes in accordance with the following criteria occur:

. . .

g)	when the onset, cessation or change in intensity of any of the following weather phenomena or combinations thereof occurs:

—	freezing precipitation

—	moderate or heavy precipitation (including showers thereof)

—	thunderstorm (with precipitation)

—	duststorm

—	sandstorm;

h)	when the onset or cessation of any of the following weather phenomena or combinations thereof occurs:

—-	ice crystals

—	freezing fog

—	low drifting dust, sand or snow

—	blowing dust, sand or snow

—	thunderstorm ( without precipitation)

—	squall

—	funnel cloud (tornado or waterspout);

j)	when the amount of a cloud layer below 450 m (1 500 ft) changes:

1)	from SKC, FEW or SCT to BKN or OVC; or

2)	from BKN or OVC to SKC, FEW or SCT;

k)	when cumulonimbus clouds develop or dissipate; and

l)	when the sky is obscured and the vertical visibility is improving and changes to or passes through one or more of the following values, or when the vertical visibility is deteriorating and passes through one or more of the following values: 30, 60, 150 or 300 m (100, 200, 500 or 1 000 ft).

. . .

APPENDIX 5. TECHNICAL SPECIFICATIONS

RELATED TO FORECASTS

(See Chapter 6 of this Annex)

1. CRITERIA RELATED TO TAF

. . .

1.3 Use of change groups

1.3.1 Recommendation.— The criteria used for the inclusion of change groups in TAF or for the amendment of TAF should be based on the following:

a)	when the mean surface wind direction is forecast to change by 60° or more, the mean speed before and after the change being 20 km/h (10 kt) or more;

b)	when the mean surface wind speed is forecast to change by 20 km/h (10 kt) or more;

c)	when the variation from the mean surface wind speed (gusts) is forecast to increase by 20 km/h (10 kt) or more, the mean speed before and after the change being 30 km/h (15 kt) or more;

d)	when the surface wind is forecast to change through values of operational significance. The threshold values should be established by the meteorological authority in consultation with the appropriate ATS authority and operators concerned, taking into account changes in the wind which would:

1)	require a change in runway(s) in use; and

2)	indicate that the runway tailwind and crosswind components will change through values representing the main operating limits for typical aircraft operating at the aerodrome;

e)	when the visibility is forecast to improve and change to or pass through one or more of the following values, or when the visibility is forecast to deteriorate and pass through one or more of the following values:

1)	800, 1 500 or 3 000 m;or

2)	5 000 m in cases where significant numbers of flights are operated in accordance with the visual flight rules;

f)	when any of the following weather phenomena or combinations thereof are forecast to begin or end or change in intensity:

—	freezing precipitation

—	moderate or heavy precipitation (including showers thereof)

—	thunderstorm (with precipitation)

—	duststorm

—	sandstorm

;

g)	when the onset or cessation of any of the following weather phenomena or combinations thereof are forecast to begin or end:

—	ice crystals

—	freezing fog

—	low drifting dust, sand or snow

—	blowing dust, sand or snow

—	thunderstorm ( without precipitation)

— squall

—	funnel cloud (tornado or waterspout);

h)	when the height of base of the lowest layer or mass of cloud of BKN or OVC extent is forecast to lift and change to or pass through one or more of the following values, or when the height of the lowest layer or mass of cloud of BKN or OVC extent is forecast to lower and pass through one or more of the following values:

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

2)	450 m (1 500 ft), in cases where significant numbers of flights are operated in accordance with the visual flight rules;

i)	when the amount of a layer or mass of cloud below 450 m (1 500 ft) is forecast to change:

1)	from SKC, FEW or SCT to BKN or OVC; or

2)	from BKN or OVC to SKC, FEW or SCT;

j)	when cumulonimbus clouds area forecast to develop or dissipate;

j)	when the vertical visibility is forecast to improve and change to or pass through one or more of the following values, or when the vertical visibility is forecast 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) .

. . .

2.2.4 Weather phenomena

2.2.4.1 The trend forecast shall indicate the expected onset, cessation or change in intensity of one or more of the following weather phenomena or combinations thereof:

—	freezing precipitation

—	moderate or heavy precipitation (including showers thereof)

—	duststorm

—	sandstorm

—	other weather phenomena given in Appendix 3, 4.4.2.3, only if they are expected to cause a significant change in visibility.

2.2.4.2 The trend forecast shall indicate the expected onset or cessation of one or more of the following weather phenomena or combinations thereof:

—	ice crystals

—	freezing fog

—	low drifting dust, sand or snow

—	blowing dust, sand or snow

—	thunderstorm (with or without precipitation)

—	squall

—	funnel cloud (tornado or waterspout).

2.2.4.3	The total number of phenomena reported in 2.2.4.1 and 2.2.4.2 above shall not exceed three.

2.2.4.4 The expected end of occurrence of the weather phenomena shall be indicated by the abbreviation "NSW".

. . .

Table A5-1. Template for TAF

Key:	M	=	inclusion mandatory, part of every message

C	=	inclusion conditional, dependent on meteorological conditions or method of observation

O	=	inclusion optional

Note 1.— The ranges and resolutions for the numerical elements included in TAF are shown in Table A5-3 of this appendix.

Note 2.— The explanations for the abbreviations used can be found in the Procedures for Air Navigation Services — ICAO Abbreviations and Codes (PANS-ABC, Doc 8400).

Element as specified in Chapter 6	Detailed content	Template(s)	Examples
Identification of the type of forecast (M)	Type of forecast (M)	TAF or TAF AMD or TAF COR	TAF

TAF AMD
Location indicator (M)	ICAO location indicator (M)	nnnn	YUDO1
Time of issue of forecast (M)	Day and time of issue of the forecast in UTC (M)	nnnnnnZ	160000Z
Identification of a missing forecast (C)	Missing forecast identifier (C)	NIL	NIL
END OF TAF IF THE FORECAST IS MISSING.
Days and period of validity of forecast (M)	Days and period of the validity of the forecast in UTC (M)	nnnnnnnn	16061624

08120918
Identification of a cancelled forecast (C)	Cancelled forecast identifier (C)	CNL	CNL
END OF TAF IF THE FORECAST IS CANCELLED.
Surface wind (M)	Wind direction (M)	nnn or VRB2	24015KMH; VRB04KMH

(24008KT); (VRB02KT)

19022KMH

(19011KT)
Wind speed (M)	[P]nn[n]	00000KMH

(00000KT)

140P199KMH

(140P99KT)
Significant speed variations (C)3

G[P]nn[n]	12012G35KMH

(12006G18KT)

24032G54KMH

(24016G27KT)
Units of measurement (M)	KMH (or KT)
Visibility (M)	Prevailing visibility (M)	nnnn	C

A

V

O

K	0350	CAVOK

7000

9000

9999
Weather (C)4, 5	Intensity of weather

phenomena (C)6	– or +	—
Characteristics and type of weather phenomena (C)7	DZ or RA or

SN or SG or

PL or DS or

SS or

FZDZ or

FZRA or

SHGR

SHGS or

SHPL or

SHRA or

SHSN or

TSGR or

TSGS or

TSPL or

TSRA or

TSSN	IC or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or BCFG or

BLDU BLSA BLSN DRDU DRSA DRSN FZFG MIFG PRFG	RA	HZ

+TSRA	FG

–FZDZ PRFG

+TSRASN

SNRA FG
Cloud (M)8	Cloud amount and

height of base or

vertical visibility (M)	FEWnnn

or

SCTnnn or

BKNnnn

VVnnn

or

VV ///	SKC or

NSC	FEW010	VV005	SKC

OVC020	VV///	NSC

SCT005 BKN012
Cloud type (C)4	CB	—	SCT008 BKN025CB
Temperature (O)9	Name of the element (M)	TX	TX25/1013Z TN09/1005Z

TX05/2112Z TNM02/2103Z
Maximum temperature (M)	[M]nn/
Day and time of occurrence of the maximum temperature (M)	nnnnZ
Name of the element (M)	TN
Minimum temperature (M)	[M]nn/
Day and time of occurrence of the minimum temperature (M)	nnnnZ
Expected significant changes to one or more of the above elements during the period of validity (C)4, 10	Change or probability indicator (M)	PROB30 [TEMPO] or PROB40 [TEMPO] or BECMG or TEMPO or FM
Period of occurrence

or change (M)	nnnnnnnn
Wind (C)4	nnn[P]nn[n][G[P]nn[n]]KMH

or

VRBnnKMH

(or

nnn[P]nn[G[P]nn]KT

or

VRBnnKT)	TEMPO 08150818 25070G100KMH

(TEMPO 08150818 25035G50KT)

TEMPO 22122214 17025G50KMH 1000

TSRA SCT010CB BKN020

(TEMPO 22122214 17012G25KT 1000

TSRA SCT010CB BKN020)
Prevailing visibility (C)4	nnnn	C

A

V

O

K	BECMG 30103011 00000KMH 2400 OVC010

(BECMG 30103011 00000KT 2400 OVC010)

PROB30 14121414 0800 FG
Weather phenomenon:

intensity (C)6	– or +	—	NSW	BECMG 14121414 RA

TEMPO 25032504 FZRA

TEMPO 06120615 BLSN

PROB40 TEMPO 29233001 0500 FG
Weather phenomenon: characteristics and type

(C)4, 7	DZ or RA or

SN SG

PL or DS or

SS or

FZDZ or

FZRA or

SHGR or

SHGS or

SHPL or

SHRA or

SHSN or

TSGR or

TSGS or

TSPL or

TSRA

TSSN	IC or FG or

BR SA DU HZ FU VA

SQ or PO or FC or TS or

BCFG

BLDU or

BLSA

Cloud amount and height of base or vertical visibility (C)4	FEWnnn or

SCTnnn or

BKNnnn

VVnnn

or

VV///	SKC or NSC	FM051230 15015KMH 9999 BKN020

(FM051230 15008KT 9999 BKN020)

BECMG 16181620 8000 NSW NSC
Cloud type (C)4	CB	—	BECMG 23062308 SCT015CB BKN020

Notes.—

1.	Fictitious location.

2.	To be used in accordance with 1.2.1.

3.	To be included in accordance with 1.2.1.

4.	To be included whenever applicable.

5.	One or more, up to a maximum of three, groups in accordance with 1.2.3.

6.	To be included whenever applicable in accordance with 1.2.3. No qualifier for moderate intensity.

7.	Weather phenomena to be included in accordance with 1.2.3.

8.	Up to four cloud layers in accordance with 1.2.4.

9.	To be included in accordance with 1.2.5.

10.To be included in accordance with 1.3, 1.4 and 1.5.

Table A5-2. Use of change and time indicators in TAF

Change or time

indicator	Time period	Meaning
FM	ndndnhnhnmnm	used to indicate a significant change in most weather elements occurring at ndnd day, nhnh hours and nmnm minutes (UTC);

all the elements given before "FM" are to be included following "FM" (i.e. they are all superseded by those following the abbreviation)
BECMG	nd1nd1nh1nh1nd2nd2nh2n
h2	the change is forecast to commence at nd1nd1 day and nh1nh1 hours (UTC) and be completed by nd2nd2 day and nh2nh2 hours (UTC);

only those elements for which a change is forecast are to be given following "BECMG";

the time period nd1nd1nh1nh1nd2nd2nh2nh2 should normally be less than 2 hours and in any case should not exceed 4 hours
TEMPO	nd1nd1nh1nh1nd2nd2nh2n
h2	temporary fluctuations are forecast to commence at nd1nd1 day and nh1nh1 hours (UTC) and cease by nd2nd2 day and nh2nh2 hours (UTC);

only those elements for which fluctuations are forecast are to be given following "TEMPO";

temporary fluctuations should not last more than one hour in each instance, and in the aggregate, cover less than half of the period nd1nd1nh1nh1nd2nd2nh2nh2
PROBnn	—	nd1nd1nh1nh1nd2nd2nh2n
h2	probability of occurrence (in %) of an alternative value of a forecast element or elements;

nn = 30 or nn = 40 only;

to be placed after the element(s) concerned	—
TEMPO	nd1nd1nh1nh1nd2nd2nh2n
h2	probability of occurrence of temporary fluctuations

. . .

TAF for YUDO (Donlon/International)*:

TAF YUDO 160000Z 16061624 13018KMH 9000 BKN020 BECMG 16061608 SCT015CB BKN020 TEMPO 16081612 17025G45KMH 1000 TSRA SCT010CB BKN020 FM161230 15015KMH 9999 BKN020

Meaning of the forecast:

TAF for Donlon/International* issued on the 16th of the month at 0000 UTC valid from 0600 UTC to 2400 UTC on the 16th of the month; surface wind direction 130 degrees; wind speed 18 kilometres per hour; visibility 9 kilometres, broken cloud at 600 metres; becoming between 0600 UTC and 0800 UTC on the 16th of the month, scattered cumulonimbus cloud at 450 metres and broken cloud at 600 metres; temporarily between 0800 UTC and 1200 UTC on the 16th of the month surface wind direction 170 degrees; wind speed 25 kilometres per hour gusting to 45 kilometres per hour; visibility 1 000 metres in a thunderstorm with moderate rain, scattered cumulonimbus cloud at 300 metres and broken cloud at 600 metres; from 1230 UTC on the 16th of the month surface wind direction 150 degrees; wind speed 15 kilometres per hour; visibility 10 kilometres or more; and broken cloud at 600 metres.

* Fictitious location

Note.— In this example, the primary units "kilometre per hour" and "metre" were used for wind speed and height of cloud base, respectively. However, in accordance with Annex 5, the corresponding non-SI alternative units "knot" and "foot" may be used instead.

Example A5-2. Cancellation of TAF

Cancellation of TAF for YUDO (Donlon/International)*:

TAF AMD YUDO 161500Z 16061624 CNL

Meaning of the forecast:

Amended TAF for Donlon/International* issued on the 16th of the month at 1500 UTC cancelling the previously issued TAF valid from 0600 UTC to 2400 UTC on the 16th of the month.

* Fictitious location

. . .

ATTACHMENT B. OPERATIONALLY DESIRABLE

ACCURACY OF FORECASTS

Note 1.— The guidance contained in this table relates to Chapter 6 — Forecasts, in particular to 6.1.1.

Note 2.— If the accuracy of the forecasts remains within the operationally desirable range shown in the second column, for the percentage of cases indicated in the third column, the effect of forecast errors is not considered serious in comparison with the effects of navigational errors and of other operational uncertainties.

Element to

be forecast	Operationally desirable

accuracy of forecasts	Minimum percentage of

cases within range
TAF
Wind direction	20	80% of cases
Wind speed	9 km/h (5 kt)

80% of cases
Visibility	200 m up to 800 m

30% between 800 m and 10 km	80% of cases
Precipitation	Occurrence or non-occurrence	80% of cases
Cloud amount	One category below 450 m (1500 ft)

Occurrence or non-occurrence of BKN or OVC between 450 m (1 500 ft) and 3 000 m (10 000 ft)	70% of cases
Cloud height	30 m (100 ft) up to 300m (1 000 ft)

30% between 300 m (1 000 ft) and 3 000 m (10 000 ft)	70% of cases
Air temperature	1 C	70% of cases

TREND FORECAST
Wind direction	20	90% of cases
Wind speed	9 km/h (5 kt)

90% of cases
Visibility	200 m up to 800 m

30% between 800 m and 10 km	90% of cases
Precipitation	Occurrence or non-occurrence	90% of cases
Cloud amount	One category below 450 m (1 500 ft)

Occurrence or non-occurrence of BKN or OVC between 450 m (1 500 ft) and 3 000 m (10 000 ft)	90% of cases
Cloud height	30 m (100 ft) up to 300 m (1 000 ft)

30% between 300 m (1 000 ft) and 3 000 m (10 000 ft)	90% of cases

FORECAST FOR TAKE-OFF