AMOSSG/3-SN No. 02

30/11/01

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

THIRD MEETING

Miami, 22 to 25 January 2002

Agenda Item	5:	Review of the requirements for meteorological observations and reports at aerodromes contained in Chapter 4 of Annex 3

DRAFT AMENDMENT TO ANNEX 3

(Presented by the Secretary)

SUMMARY
This paper presents a proposal for amendment to Annex 3 for review by the group.

1.	INTRODUCTION

1.1	The group will recall that the Annex 3 provisions relevant to the work of the group have been thoroughly reviewed at AMOSSG/1 and AMOSSG/2 Meetings. At the second meeting, the Secretary was tasked to incorporate the suggestions made by the group into the draft amendment and circulate it to the group for comment.

2.	DISCUSSION

2.1	The group may wish to note that, in addition to the changes made by the group at the AMOSSG/2 Meeting, a number of amendments were introduced by the Secretary. Some of them are purely editorial improvements while others stemming from the European Air Navigation Planning Group (EANPG) are of a more substantial nature. All the changes made by the Secretary since the AMOSSG/2 Meeting are listed below together with explanatory comments:

a)	4.1.8 — 4.1.9.	"Manual insertion"deleted as with the addition of "back-up procedures", it would be up to the State to decide what type of back-up procedures are being used;

b)	4.1.10. "or cannot be ensured by other means" deleted (as the intent of this addition was not understood);

c)	4.2.3. A new paragraph introduced in response to the EANPG Conclusion 42/17 d);

d)	4.5.8 —4.5.10. Editorial clarifications how to report directional and speed variations;

e)	4.5.10. Proposed to be upgraded to a Standard;

f)	4.6.2. Aligned with 4.6.4 and 4.6.9;

g)	4.6.7. Rounding down added (required for instrumented systems);

h)	4.6.8. Proposed to be upgraded to a Standard;

i)	4.8.8. "Small hail" reintroduced (a request by IATA);

j)	4.8.9. The distance has been reduced from 30 to 20 km as, in accordance with the Manual on the Observation of Clouds and Other Meteors (WMO – No. 407), the upper limit for hearing thunder is 20 km; "showers of ice pellets" have been deleted since the WMO – No. 407 indicates that ice pellets "generally falls from Altostratus– or Nimbostratus–clouds";

k)	4.8.10. The paragraph has been substantially simplified to align the reporting of intensities to the practices used in the United States;

l)	4.9.9. Proposed to be upgraded to a Standard (safety implications);

m)	4.11.4. Proposed to be upgraded to a Standard (safety implications);

n)	4.13. A new paragraph introduced in response to the EANPG Conclusion 42/17 e); and

o)	6.2.5. A new paragraph introduced in response to the EANPG Conclusion 42/14.

2.2	Subsequently, the study group members were invited to review and comment, as necessary, the updated draft amendment. The secretary received comments from Michel (M) and Kevin (K). Their comments, together with the Secretary's comments (S) and the proposed action is listed below. Some of the comments received relate to the current, valid Annex 3 provisions, not subject to an amendment; those are indicated with an asterisk *:

a)	*Definition (K). "Aeronautical meteorological station" is not defined. (S). The comment is not understood as the definition is included in Annex 3 — Meteorological Service for International Air Navigation;

b)	*4.1.8 (K). Suggest the last two sentences become a Standard. This can be done now and manual insertion of all elements should be required. This could be accomplished by changing 4.1.10 to a Standard and eliminating the two sentences both 4.1.8 and 4.1.9 so we do not repeat the same thing in different places.	This is currently a Recommended Practice and should remain so. The US recognizes that available automation equipment cannot fully meet aviation observation requirements which means a Standard would not be appropriate.	(S). The comments are not understood as paragraph 4.1.8 is already a Standard in Annex 3. It may be noted that to avoid redundancy, the last sentences in 4.1.8 and 4.1.9 are proposed for deletion. (K). This paragraph should include visibility as well as RVR. Visibility is critical to airport capacity as well as production of TAF. (S). Agreed. Action proposed: add visibility in 4.1.8 and 4.1.9. (K). Why was Note 2 deleted?. (S). Note 2 has not been deleted (according to the ICAO editorial practice, paragraphs and notes without changes are not repeated in amendment proposals);

c)	4.1.10. (K). Change to a Standard and add the Human Factors information. (S). The Human Factors principle is already included in paras 4.1.8 and 4.1.9. The proposed upgrade agreed. Action proposed: upgrade to a Standard;

d)	4.2.3. (K). The US requirement is to have two reports not less than 30 minutes nor more than 1 hour apart. This allows for an adequate trend and enough information for the development of a TAF. Also, if true automation is involved the status of the airport is not material to the issue unless the automated system is turned off. (S). The paragraph is in accordance with the EANPG Conclusion 42/17 d). (K) Why was the current 4.2.3 eliminated? (S). The current 4.2.3 has not been eliminated, it will be re-numbered as 4.2.4;

e)	4.3.3. (K). See comment on 4.2.3. (S). See the Secretary's comments under d) above;

f)	* 4.5.1. (K). Automated systems should be capable of displaying both magnetic and true wind directions. (S). This is implicit in ICAO Annexes and PANS; Annex 3 calls for the use of "true north" while the Procedures for Air Navigation Services — Rules of the Air and Air Traffic Services (Doc 4444) requires that the wind information be displayed in relation to the "magnetic north". Detailed guidance has been included in ICAO manuals;

g)	4.5.4, 4.6.4, 4.8.5 and 4.9.5. (K). The phrase "as determined by local conditions" should be removed from all paragraphs in this chapter since it only weakens the intent of the guidelines being developed and since the guidance for siting sensors is clear on how to do this. This allows too much local variation. The siting Standards provide guidance when the exact Standard cannot be met. (S). Agreed. Action proposed: delete the words "as determined by local conditions";

h)	* 4.5.5. (K). As written this means that the MET office will always get magnet vs true direction since this is what they operate with. Suggest you simply state that displays in MET office should be capable of displaying both true and magnetic wind direction. Do not think it is appropriate to require instrumentation in an air traffic facility. (S). This is part of a long-standing Standard and there is nothing wrong to state a requirement for the MET authority to provide wind information to ATS units. Furthermore, similar requirements are reflected in a Standard in Annex 11 — Air Traffic Services;

i)	4.5.7. (K). At best this should be a Recommended Practice. This group has not got the charge to tell air traffic how to operate. (S). The proposal is in accordance with the consensus reached at the AMOSSG/1 and AMOSSG/2 Meetings. Furthermore, it is not stating how the ATS units should operate; it is simply stating a long-standing requirement addressed to the MET authority to provide 2-minute means to ATS units. Moreover, a similar requirement is already included in the Procedures for Air Navigation Services — Rules of the Air and Air Traffic Services (Doc 4444) addressed to the ATS authority;

j)	4.5.8 b) 1) and 2); d). (K). b) 1) should read "3 knots or more" and b) 2) "less than 3 knots". This is considered important for smaller aircraft and aircraft operating near the maximum limits of their performance envelope. (S) Agreed in principle. Action proposed: amend as suggested. Note, however, that this amendment would involve software changes at most aerodromes, since Kevin's proposal is an amendment to the current Annex 3 provisions. (K) d) If it can be measured it should be reported. This appears to be an arbitrary cutoff that has no relation to aviation. * (S). The upper limit is part of the current Annex 3 provisions. It was necessary to introduce an upper limit for the range of the wind speeds for data link applications. The users were consulted and they indicated that there was no operational requirement to give detailed wind information for winds 200 km/h (100 kt) or more. Finally, it may be noted that a note has been added to the WMO Manual on Codes (WMO—No. 306) to permit the use of wind speeds up to 200 kt to accommodate the US practice to use METARs for synoptic purposes. (K). This should remain a Recommendation unless the above suggestions are incorporated. (S). The upgrade was agreed at the AMOSSG/1 and AMOSSG/2 Meetings;

k)	* 4.5.8 b) 2). (M) Note that with the insertion of new definition for the reporting of variations in the mean wind, VRB with wind speed equal 3 kt or less will be very frequent. (S). This is already part of existing provisions (Appendix 2 to Annex 3 refers);

l)	* 4.6.1. (K) The visibility definition proposed for chapter one is not clear. The US will continue to report in miles. Making this a Standard will simply require a difference be filed by US (S). The US has already filed a difference to Annex 5 — Units of Measurement to be Used in Air and Ground Operations and it is felt that it is important for safety reasons to know whether the standard units are used or not. The definition is currently part of Annex 3 provisions. It should be pointed out that the definition took more than ten years to be developed and it involved a number of formal consultations with States and international organizations; also WMO and its relevant commissions (i.e. CIMO and CAeM) were an integral part of the development process. The present formulation reflects well the aeronautical requirements;

m)	4.6.4. (K) There is no definition of an "instrumented system". (S). Initially, the Secretary proposed the use of "scatter meters" in this context; however, the study group felt that it was too restrictive and preferred the general term "instrumented systems";

n)	4.6.4. (M). It may be useful and consistent with 4.7.5 to add that "when instrumented systems are used, the visibility should be measured at a height of approximately 2.5 m". (S). Agreed. Action proposed: Add the sentence as proposed;

o)	4.6.6. (M) It may be useful to indicate into some manual the way the average should be calculated; such a manual should be elaborated somehow and given as a reference into this paragraph of the Annex 3. We consider that the average should be calculated from the extinction coefficient and not from the visibility values. (S). Agreed in principle. However, a reference cannot be provided before necessary guidance material has been developed. Moreover, the method of averaging should also be addressed in connection with RVR;

p)	* 4.6.6. (K).	Is this the WMO standard? We disagree that algorithms should no longer be used in marked discontinuity situations. Our experience tells us time averaging still works, for the most part, in these conditions. (S). This is not a WMO standard; it is simply aligning the averaging of visibility measurements to that of RVR. The discontinuity clause has been part of Annex 3 for a number of years and were initially introduced at the request of users;

q)	* 4.6.7 (K). This is completely unacceptable to us. We have airports with visual approaches which require the reporting of six miles or the approach can not be used, thus reducing capacity. We see no reason why the needs of aviation can not be accommodated by reporting out to 10 miles. US general aviation needs would not be served by this proposal. (S). The upper limit of 10 km and the reporting scale have been part of Annex 3 provisions for decades;

r)	* 4.6.10 (K). We completely disagree. The US uses prevailing visibility concept to determine the entry in the body of the report. That is, the greatest visibility over at least half the horizon, or if the visibility is varying rapidly during the observation period, use the average of all observed values. We also introduce the concept of sector visibility which is reported if either sector or prevailing is less than 3 miles or considered operationally significant. (S). The use of "minimum visibility" is part of current Annex 3 provisions. The proposal for introducing "prevailing visibility" is included in Appendix B;

s)	* 4.7.3 (K). The entire section on RVR needs to be studied further. The US will continue to report RVR in feet. (S). The section concerning RVR has been reviewed a few years ago by the RVRSG (since disbanded) and has been substantially updated as a result of Conclusions made by the EANPG. The exclusive use of metres for reporting RVR is in line with Annex 5 provisions. Furthermore, the group may wish to note that the recent ICAO Assembly has reinstated the resolution calling for the exclusive use of Annex 5 units of measurement in all ICAO publications;

t)	4.7.3 and 4.7.15 (M). The maximum limit is 1 500 m in 4.7.3 and 2 000 m in 4.7.15; may be the paragraphs should be reworded to avoid any inconsistency or misunderstanding. (S). The point raised is well understood; however, it should be noted that paragraph 4.7.3 indicates when States have an obligation to report RVR while 4.7.15 simply provides the reporting range to be used. Action proposed: delete "assessments of" in 4.7.15;

u)	* 4.7.9. (K). The newest RVR equipment does not require the observer to enter reports, it is done automatically. The US will not comply with this Standard. Suggest it be changed to a Recommended Practice. (S). The comment is not understood. Moreover, 4.7.9 is currently a Standard in Annex 3;

v)	* 4.7.10. (K).	True RVR reports should be done by machine not humans. The machine measures the same every time and because of the precision required in these reports the normal human variations are not acceptable. Human reports of this nature are called RVV in the US. (S). RVV is not used internationally; according to international provisions RVR can be assessed by human observers. Annex 3 does require the use of instrumented RVR measurements for Category II and III operations (subject to a Standard 4.1.8), while for other operations States have still an option to use human observers;

w)	4.7.12. (M). This paragraph should be discussed again during the next AMOSSG taking into account the study Michel has been tasked with. (S). Agreed;

x)	4.7.13 (K). This should be a Standard as it can render certain approaches unavailable. (S). Agreed. Action proposed: upgrade to a Standard;

y)	4.7.17 b) and 4.7.18 a) (M). It is not possible for the MET observer to know which runway is in use . For that reason it is not feasible to transmit only information concerning the runway in use at one time (in local reports) or the value for touchdown zone (in METAR/SPECI) which also depends on the runway in use. The proposal is: either to reword the paragraphs involved in the way that the information shall be passed for all runway available, or to keep the paragraphs as Recommended Practices. (S). The first comment is not understood since in local reports all available information should be included. With regard to reports in the METAR/SPECI code forms, the limit of four runways was initially established to avoid the messages becoming unnecessarily lengthy. However, it could be argued that the limit is not necessary any longer. Action proposed: delete "up to a maximum of four";

z)	4.8.1 (K). This should remain a Recommendation and should be changed to weather in the vicinity should be reported if it is operationally significant to AT. (S). The upgrade was agreed at the AMOSSG/2 Meeting; the obligation to observe all the elements included in meteorological reports (except for supplementary information) was proposed to be subject to a Standard by the group;

aa)	4.8.1 (M). We do not agree with raising this paragraph as a Standard; that should be discussed during AMOSSG/3. (S). See comments under z) above;

bb)	4.8.9 and 4.8.10 (M). The definitions in 4.8.9 for the use of "TS" and in 4.8.10. for the use of "VC" are not consistent, regarding the observation of TS; the proposal is to delete "and TS" in paragraph concerning VC. (S). Agreed; there is indeed overlap between "TS" and "VCTS". Action proposed: delete "and TS" in 4.8.10;

cc)	4.8.9 (K). Automated reporting of TS in the US is done 0-5 miles TS at the station, 5-10 TS in the vicinity of the station (VCTS) and 10-30 miles LTG distant with a direction (LTG DSNT SW).	Add to the definition "…or if lightening is observed overhead and local noise prevents hearing thunder." (S) The use of "VC" in the US is noted. With regard to the proposed wording, it is felt that the current wording already covers the case when the thunder is not heard;

dd)	* 4.8.4 (K). This is redundant. See comment 4.1.8. (S). The secretary does not share this point of view; this paragraph refers to present weather in particular. Action proposed: add "present" before "weather";

ee)	4.8.6 (K). This should be a general statement at the start of the chapter and not repeated every time a sensor is mentioned. (S). This cannot be done for the time being since for some elements the displays are mandatory, i.e. subject to a Standard while for other elements they are only recommended;

ff)	4.8.9 (K). The US NWS disagrees with this deletion as they contend that IP can fall as showers. (S). The deletion was based on guidance given in the Manual on the Observation of Clouds and Other Meteors (WMO – No. 407);

gg)	* 4.9.2 (K). How will this work with GPS approaches which have no markers. Suggest a distance from the approach end of the runway. (S). The issue was already addressed by the group and the relevant distance is indicated in 4.9.5;

hh)	* 4.9.4 (K). This is redundant. See comment for 4.1.8. It should be stated once at beginning of chapter. (S). See the Secretary's comments under dd);

ii)	4.9.6 (K). This is redundant. (S). See the Secretary's comments under ee);

jj)	*4.9.7 (K). The bases of clouds should be related to the published height of the aerodrome. Pilots would be expected to make any required adjustments; (S). The provision has been in Annex 3 for years;

kk)	* 4.9.8 (K). This does not support GA operations and the US will continue to report clouds present at all altitudes. Our automated systems currently report up to FL120 and the newer ones will report up FL250. We will also report TCU in the body of the report. (S). These are part of current requirements and the intent of the new paragraph is simply to clarify the existing provisions;

ll)	4.9.9 and 4.9.10 (M). The reporting of TCU should be discussed in AMOSSG once more; what is the reason for deleting the observation of TCU in METAR/SPECI but keeping it in local reports? The proposal is either to report the TCU in the two messages or to ignore them in the two messages. (S). The initial proposal by AMOSSG was based on the fact that this information would not be required at the flight planning stage and that hence, it could be deleted from reports in the METAR/SPECI code forms;

mm)	* 4.9.9 c) (K).	The US uses 500 ft above 5 000 ft and 1 000 ft above 10 000 ft. (S). The reporting scale is in agreement with the current Annex 3 provisions;

nn)	* 4.9.9 d) (K). The US will use "CLR BLO 120" (250 for newer systems) for automated reports and will not use either of the codes shown. (S). The use of "CAVOK" and "SKC" is in agreement with the current Annex 3 provisions and they are part of ICAO provisions for decades;

oo)	* 4.9.9 e) (K). The US will use "CLR BLO 120" (250 for newer systems) for automated reports and CLR for manual reports when no clouds are present. We will not use the contraction in the paragraph as we report all clouds present that can be observer from the reporting station. (S). The use of "NSC" is in agreement with the current Annex 3 provisions;

pp)	* 4.10.3 (K). Should use the same coding in all reports. All users recognize "M" when associated with a temperature as meaning "minus". (S) The use of "MS" is in accordance with current provisions; in principle, it could be proposed for change; however, it will involve software changes in most operational systems;

qq)	4.11.1 (K). Altimeter information #########. (S). The comment is not understood;

rr)	4.11.2 (K). This is redundant as it should be addressed as a general statement for all elements right up front in the Chapter. (S). See the Secretary's comments under ee);

ss)	* 4.12.2 (K). This is redundant and should be addressed upfront in the chapter as a general statement. (S). See the Secretary's comments under dd);

tt)	* 4.12.3 (K). The US does not report recent weather and sees no useful purpose in doing so. (S). This was addressed at the AMOSSG/2 and the requirement was reconfirmed by users;

uu)	* 4.12.5 (K).	The US does not report wind shear in METAR because that information is available at a limited number of sites and lack of a wind shear report would cause confusion as to the absence of it or the system at the airport is incapable of reporting it. (S). To be reported only "where local circumstances so warrant";

vv)	* 4.12.6 b). (K). This is not meteorological information and the US does not report it in METAR/SPECI code. It is always available in NOTAM code if there is an operationally significant report required. (S). Included in METARs in response to a request by the EANPG;

ww)	4.13.1 (K). The US considers automated systems capable of reporting information required for flight as well as for development of TAF. Also in the US there are, with rare exceptions, no "non-operational hours of an aerodrome". All public use aerodromes are available 24 hours per day unless NOTAM or published information indicates otherwise. (S). The formulation is based on the Conclusion 42/17 e) of the EANPG;

xx)	4.13.3 (K). The US will continue to report prevailing visibility, which is the greatest visibility the can be observed over at least half the horizon. At aerodromes that have unusual visibility issues we use what are called "met discontinuity sensors" and provide that visibility value in the remarks. (S). The introduction of "prevailing visibility" is subject to a parallel amendment in Appendix B to this paper;

yy)	4.13.4 and 4.13.5 (K) Delete the words "to the extent possible" as this would allow just about any present weather or cloud element to not be reported. (S) Agreed. Action proposed: delete "to the extent possible";

zz)	4.13.6 (K). Delete the word "not". The US includes supplementary information called REMARKS of both a manual and automated nature. It is important to know if the automated system is capable of reporting all the information it is supposed to. The remarks indicate that the system cannot report TS with "TSNO" in the remarks. This true for FZ precipitation and other aviation critical parameters. (S). There seems to be a misinterpretation, i.e. the "Remarks section" includes national information, not subject to international provisions and which is not disseminated beyond the State concerned while "supplementary information" is subject to international provisions and detailed in Annex 3. Moreover, based on the Kevin's earlier comments, it seems that the US includes nothing under the supplementary information in reports in the METAR/SPECI code forms (since "recent weather" and "wind shear" are not reported in METAR reports);

aaa)	4.14.1 (K). The US code for METAR/SPECI reports is "METAR KXXX date time group AUTO then the report in ICAO format. The AUTO may be replaced by COR if a correction to a previously filed report is required. (S). The format of the report is shown in Appendix 2 to Annex 3, not under Section 4.14;

bbb)	4.14.1 h) (K). The US reports both CB and TCU in the body of the report. Delete the phrase "…in local routine and special reports." TCU and CB should be included in all types of reports. (S). See the Secretary's comments under ll) above;

ccc)	4.14.1 k). (K).	Add back in as supplementary information in automated systems is critical to aviation (see 4.13.6 comment). (S). See the Secretary's comment under zz);

ddd)	4.14.1 Note 2. (K) Restore note 2 since we think TCU should be reported. (S). Agreed. Action proposed: re-introduce Note 2;

eee)	* 4.14.3 (K). The US will not do this as it does not adequately support airport operations at some airports and is a detriment to general aviation. (S). The use of "CAVOK" has been part of ICAO provisions for decades; and

fff)	6.2.5 (M). The insertion of the note "reports in the METAR/SPECI code forms identified with "AUTO" cannot at the present time be used for review of aerodrome forecasts" is not acceptable because it is not exact. The information included in AUTO METAR/SPECI associated with other existing means of observation (satellite, radar) can be used in an efficient way for review of aerodrome forecasts. (K). The US allows the forecaster some discretion in this area and we will continue to do so. The US uses AUTO reports to monitor conditions for production of TAF and will continue to do so. (S). The formulation reflects the opinion of the Meteorological Group (METG) of the EANPG which stated that "it was also agreed that fully automated meteorological reports should at present not be used for preparation and review of aerodrome forecasts" (EANPG/42 report refers).

2.3	With regard to the introduction of "prevailing visibility", the following comments were made concerning the draft amendment (Appendix B refers):

a)	Definition for "prevailing visibility" (M). It should be investigated again by the AMOSSG. Given that, some paragraphs under 4.6 should be adapted later on (e.g. new 4.6.10). (S). The ANC has instructed the Secretariat to develop an amendment introducing "prevailing visibility" as defined in the North American Region (subject to editorial changes to render the language comparable to the one used in ICAO Annexes). Under these circumstances, no other concepts of "prevailing visibility" can be considered. The area where input from the group is required is how to report directional variations when the "prevailing visibility" concept is being used;

b)	Definition for "prevailing visibility" (K). Suggest something like this as a definition: "Visibility is a measure of the opacity of the atmospheres. For aviation observations it is the greatest distance the observer can see a dark (black?) object during daylight or an unfocused light at night. For automated systems it is the derived visibility that represents the state of the atmosphere at the point of observation that would be representative of the visibility at the aerodrome". (S). With regard to the general definition of "visibility", see the Secretary's comments under 2.2 l). With regard to the specific definition of "prevailing visibility", as indicated under a) above, the Secretariat is tasked to develop a proposal based on the definition as indicated in Appendix B. Furthermore, it would not be acceptable to have another "downgraded" version of the definition applicable for automated systems;

c)	4.6.9 b). (K). The US reports the sector visibility in the remarks when the sector visibility differs from the prevailing visibility by one or more reportable values and either the prevailing or sector visibility is less than 3 miles. (FMH-1, 6.5.7) Sector is defined as a 45-degree segment of the horizon circle. (S). The "Remarks Section" could not be used in international provisions since "the indicator RMK denotes the beginning of a section containing information included by national decision which shall not be disseminated internationally" (WMO Manual on Codes, paragraph 15.15 refers); and

d)	4.6.9 c). The US uses variable prevailing visibility which is described as prevailing visibility rapidly fluctuating by ½ mile or more and the prevailing visibility is less than 3 miles (FMH-1, 6.4.5). (S). The group should consider, based on the views expressed by users, whether the indication of variable visibility or minimum visibility would better meet the operational requirements.

2.4	The group may wish to note that, since the AMOSSG/2 Meeting, an additional task entitled MET-0101: Aeronautical MET data representation and codes has been added to the Technical Work Programme by the ANC. One of the objectives of this task is to "amend Annex 3 to allow the use of the BUFR and CREX code forms to transmit meteorological reports and aerodrome forecasts and to specify how the information is to be presented to aeronautical users". The group may wish to consider the draft amendment in this regard included in Appendix A. It should be noted that the terms "routine reports in the METAR code form", "special reports in the SPECI code form" and "aerodrome forecasts in the TAF code form" are proposed to be amended all through Annex 3 to read "METAR reports", "SPECI reports" and "TAF forecasts", respectively. Moreover, paragraphs 4.2.2, 4.3.2 and 6.2.3 would have to be amended as shown in Appendix A.

2.5	Finally, it may be noted that the Meteorological Communications Group (MOTNEG) of the EANPG at its seventh meeting held in 2001 called for the inclusion of identifiers for corrected ("COR") and nil ("NIL") reports in METAR and SPECI reports and TAF forecasts. Theses draft amendments have been included in the relevant templates.

3.	ACTION BY THE GROUP

3.1	The group is invited to review:

a)	draft amendment to Annex 3 related to the overall work undertaken with the assistance of the AMOSSG contained in Appendix A to this paper; and

b)	draft amendment to Annex 3 related to the proposal to introduce "prevailing visibility" contained in Appendix B to this paper.

— — — — —

AMOSSG/3-SN No. 02

Appendix A

APPENDIX A

AMENDMENT PROPOSALS TO CHAPTER 4 (relevant parts)

OF ANNEX 3 INCLUDING ALL THE ISSUES ADDRESSED EXCEPT FOR "PREVAILING VISIBILITY" FOR INCLUSION IN AMENDMENT 73

AMENDMENT PROPOSALS TO

ANNEX 3 FOR INCLUSION IN AMENDMENT 73

(applicable November 2004)

INTERNATIONAL STANDARDS

AND RECOMMENDED PRACTICES

METEOROLOGICAL SERVICE

FOR INTERNATIONAL AIR NAVIGATION

Editorial Note: —	The dashed line indicates the limit between prospective "core" Standards and Recommended Practices (SARPs) and "technical specifications". If the split of Annex 3 is carried out, the notes under the templates should be replaced by references to the relevant "requirement or technical specification". The sub-headings have been introduced for clarity and they would only be retained in the part including the "requirement or technical specifications".

CHAPTER 4. METEOROLOGICAL OBSERVATIONS AND REPORTS

• • • • •

4.1.8 At aerodromes, with runways intended for Category II and III instrument approach and landing operations, automated equipment for measuring or assessing, as appropriate, and for monitoring and remote indicating of surface wind, visibility, runway visual range, height of cloud base, air and dew-point temperatures and pressure values shall be installed to support approach and landing and take-off operations. These devices shall be integrated automatic systems for acquisition, processing, dissemination and display in real time of the meteorological parameters affecting landing and take-off operations. The design of integrated automatic systems shall observe Human Factors principles and include back-up procedures.

Note 1.— Categories of precision approach and landing operations are defined in Annex 6, Part I.

• • • • •

4.1.9 Recommendation.— At aerodromes, with runways intended for Category I instrument approach and landing operations, automated equipment for measuring or assessing, as appropriate, and for monitoring and remote indicating of surface wind, visibility, runway visual range height of cloud base, air and dew-point temperatures and pressure values should be installed to support approach and landing and take-off operations . These devices should be integrated automatic systems for acquisition, processing, dissemination and display in real time of the meteorological parameters affecting landing and take-off operations. The design of integrated automatic systems should observe Human Factors principles and include back-up procedures.

4.1.10 Where an integrated automatic system is used for the dissemination/display of meteorological information, it shall be capable of accepting the manual insertion of data covering those meteorological elements which cannot be observed by automatic means.

• • • • •

4.2 Routine observations

and reports

• • • • •

4.2.2 Reports of routine observations shall be issued as:

a)	local routine reports in abbreviated plain language, in accordance with the template shown in Appendix 2, only for dissemination at the aerodrome of origin (intended for arriving and departing aircraft); and

b)	METAR reports , in accordance with the template shown in Appendix 2, for dissemination to other aerodromes beyond the aerodrome of origin (mainly intended for flight planning, VOLMET broadcasts and D-VOLMET) in the METAR or BUFR code forms prescribed by the World Meteorological Organization.

Note 1.— Meteorological information used in ATIS (voice-ATIS and D-ATIS) is to be extracted from the local routine report, in accordance with Annex 11, 4.3.6.1 g).

Note 2.— The METAR and BUFR code forms are contained in WMO Publication No. 306, Manual on Codes, Volume I.1, Part A — Alphanumeric Codes and Volume I.2, Part B — Binary Codes, respectively.

Note 3.— Examples of local routine reports and METAR reports are given in Appendix 2.

Editorial Note.—	Amend "routine reports in the METAR code form" to read "METAR reports" all through Annex 3.

4.2.3	At aerodromes that are not operational throughout 24 hours in accordance with 4.2.1, routine reports in the METAR code form shall be issued at least two hours prior to the aerodrome resuming operations.

• • • • •

4.3 Special observations

and reports

• • • • •

4.3.2 Reports of special observations shall be issued as:

a)	local special reports in abbreviated plain language, in accordance with the template shown in Appendix 2, only for dissemination at the aerodrome of origin (intended for arriving and departing aircraft); and

b)	SPECI reports , in accordance with the template shown in Appendix 2, for dissemination to other aerodromes beyond the aerodrome of origin (mainly intended for flight planning, VOLMET broadcasts and D-VOLMET) in the SPECI or BUFR code forms prescribed by the World Meteorological Organization.

Note 1.— Meteorological information used in ATIS (voice-ATIS and D-ATIS) is to be extracted from the local special report, in accordance with Annex 11, 4.3.6.1 g).

Note 2.— The SPECI and BUFR code forms are contained in WMO Publication No. 306, Manual on Codes, Volume I.1, Part A — Alphanumeric Codes and Volume I.2, Part B — Binary Codes, respectively.

Note 3.— Examples of local special reports and SPECI reports are given in Appendix 2.

Editorial Note.—	Amend "special reports in the SPECI code form" to read "SPECI reports" all through Annex 3.

4.3.3	At aerodromes that are not operational throughout 24 hours in accordance with 4.2.1, special reports in the SPECI code form shall be issued at least two hours prior to the aerodrome resuming operations.

• • • • •

4.5 Observing and reporting of

surface wind

Introductory Note.— Selected criteria applicable to meteorological information referred to in 4.5 to 4.12 for inclusion in aerodrome reports are given in tabular form in Attachment C.

4.5.1 The mean direction and the mean speed of the surface wind shall be measured, as well as significant variations of the wind direction and speed, and reported to the nearest 10 degrees true and nearest 1 kilometre per hour (or 1 knot), respectively.

Representativeness:

4.5.2 Recommendation.— When local routine and special reports are used for departing aircraft, the surface wind observations for these observations should be representative of conditions along the runway; when local routine and special reports are used for arriving aircraft, the surface wind observations for these reports should be representative of the touchdown zone. Surface wind observations for local routine and special reports should be representative of conditions at a height of approximately 10 m ( 30 ft) above the runway.

4.5.3 Recommendation. — For reports in the METAR/SPECI code forms, the surface wind observations should be representative of conditions at a height of 10 m ( 30 ft) above the whole runway where there is only one runway and the whole runway complex where there is more than one runway.

Siting:

4.5.4 Recommendation.— Representative surface wind observations should be obtained by the use of sensors appropriately sited . Sensors for surface wind observations for local routine and special reports should be sited to give the best practicable indication of conditions along the runway, e.g. lift-off and touchdown zones. At aerodromes where topography or prevalent weather conditions cause significant differences in surface wind at various sections of the runway, additional sensors should be provided.

Note.— Since, in practice, the surface wind cannot be measured directly on the runway, surface wind observations for take-off and landing are expected to be the best practicable indication of the winds which an aircraft will encounter during take-off and landing.

Displays:

4.5.5 Surface wind displays relating to each sensor shall be located in the meteorological station with corresponding displays in the appropriate air traffic services units. The displays in the meteorological station and in the air traffic services units shall relate to the same sensors, and where separate sensors are required as specified in 4.5.4, the displays shall be clearly marked to identify the runway and section of runway monitored by each sensor.

4.5.6	Recommendation.— Where multiple sensors are installed, the mean values of, and significant variations in, the surface wind direction and speed for each sensor should be derived and displayed by automatic equipment.

Averaging:

4.5.7 The averaging period for surface wind observations shall be:

a)	2 minutes for local routine and special reports and for wind displays in air traffic services units; and

b)	10 minutes for reports in the METAR/SPECI code forms, except that when the 10-minute period includes a marked discontinuity in the wind direction and/or speed, only data occurring since the discontinuity should be used for obtaining mean values, hence the time interval in these circumstances should be correspondingly reduced.

Note.— A marked discontinuity occurs when there is an abrupt and sustained change in wind direction of 30 or more, with a wind speed of 20 km/h (10 kt) before or after the change, or a change in wind speed of 20 km/h (10 kt) or more, lasting at least 2 minutes.

Reporting:

4.5.8 In local routine and special reports and in reports in the METAR/SPECI code forms:

a)	the units of measurement used for the wind speed shall be indicated;

b)	variations in the mean wind direction shall be reported as follows, if the total variation is 60 or more:

1)	when the total variation is between 60 and 180 and the wind speed is 6 km/h (3 kt) or more such directional variations shall be reported as the two extreme directions between which the surface wind has varied during the past 10 minutes: and

2)	when the total variation is 180 or more; or when the total variation is between 60 and 180 and the wind speed is less than 6 km/h (3 kt), the wind direction shall be reported as variable with no mean wind direction.

c)	variations from the mean wind speed (gusts) during the past 10 minutes shall be reported when the maximum wind speed exceeds the mean speed by 20 km/h (10 kt) or more;

d)	when a wind speed of 200 km/h (100 kt) or more is reported, it shall be indicated as 200 km/h (100 kt); and

e)	when the 10-minute period includes a marked discontinuity in the wind direction and/or speed, only variations from the mean wind direction and mean wind speed occurring since the discontinuity shall be reported. The variations from the mean wind direction and mean wind speed shall be derived:

1)	for automated systems from the actual measured values of wind direction and speed, and not from the 2-minute and 10-minute running averages required under 4.5.7.; and

2)	for non-automated systems from the wind direction and speed displays or from the anemograph recorder trace if available .

Note.— See note under 4.5.5.

4.5.9	Recommendation.— In local routine and special reports:

a)	if the surface wind is observed from more than one location along the runway, the locations for which these values are representative should be indicated, ;

b)	when there is more than one runway in use and the surface wind related to these runways is observed, the available wind values for each runway should be given , and the runways to which the values refer should be reported;

c)	when variations from the mean wind direction are reported in accordance with 4.5.8 b) 2), the two extreme directions between which the surface wind has varied should be reported ;

d)	when variations from the mean speed (gusts) are reported in accordance with 4.5.8 c), they should be reported as the maximum and minimum values of the wind speed attained . ;

4.5.10	In reports in the METAR/SPECI code forms, when variations from the mean wind speed (gusts) are reported in accordance with 4.5.8 c),
the maximum value of the wind speed attained shall be reported.

4.6 Observing and reporting of visibility

4.6.1 The visibility as defined in Chapter 1 shall be measured or observed , and reported in metres and kilometres in accordance with the reporting steps specified in 4.6.7.

Note — Guidance on the conversion of instrument readings into visibility is given in Attachment D.

Representativeness

4.6.2	Recommendation.— When local routine and special reports are used for departing aircraft, the visibility observations for these reports should be representative of conditions along the runway; when local routine and special reports are used for arriving aircraft, the visibility observations for these reports should be representative of the touchdown zone.

4.6.3	Recommendation.— For reports in the METAR/SPECI code forms, the visibility observations should be representative of the aerodrome and its vicinity; in such observations special attention should be given to significant directional variations.

Siting

4.6.4	Recommendation. — When instrumented systems are used for the measurement of visibility, representative visibility observations should be obtained by the use of sensors appropriately sited. Sensors for visibility observations for local routine and special reports should be sited to give the best practicable indications of visibility along the runway, e.g. lift-off and touchdown zones. The visibility should be measured at a height of approximately 2.5 m (7.5 ft).

Displays

4.6.5	Recommendation. —When instrumented systems are used for the measurement of visibility, visibility displays relating to each sensor should be located in the meteorological station with corresponding displays in the appropriate air traffic services units. The displays in the meteorological station and in the air traffic services units should relate to the same sensors, and where separate sensors are required as specified in 4.6.4, the displays should be clearly marked to identify the area, e.g. runway and section of runway, monitored by each sensor.

Averaging

4.6.6	Recommendation. —When instrumented systems are used for the measurement of visibility, the averaging period should be

a)	1 minute for local routine and special reports and for visibility displays in air traffic services units; and

b)	10 minutes for reports in the METAR/SPECI code forms except when the 10-minute period immediately preceding the observation includes a marked discontinuity in the visibility, only those values occurring after the discontinuity should be used for obtaining mean values.

Note.— A marked discontinuity occurs when there is an abrupt and sustained change in visibility, lasting at least 2 minutes, which reaches or passes through criteria for the issuance of special reports in the SPECI code form given in 4.3.4 e).

Reporting

4.6.7	In local routine and special reports and in reports in the METAR/SPECI code form, the visibility shall be reported in steps of 50 m when the visibility is less than 800 m; in steps of 100 m, when it is 800 m or more but less than 5 km ; in kilometre steps, when the visibility is 5 km or more but less than 10 km ; and it shall be given as 10 km when the visibility is 10 km or more , except when the conditions for the use of CAVOK apply. Any observed value which does not fit the reporting scale in use shall be rounded down to the nearest lower step in the scale.

Note.— Specifications concerning the use of CAVOK are given in 4.13.2.

4.6.8	In local routine and special reports, the units of measurement used for visibility shall be specified.

4.6.9	Recommendation.— In local routine and special reports, when instrumented systems are used for the measurement of visibility:

a)	if the visibility is observed from more than one location along the runway as specified in 4.6.2, the values representative of the touchdown zone should be reported first, followed, as necessary, by the values representative of the mid-point and stop-end of the runway, and the locations for which these values are representative should be indicated ; and

b)	when there is more than one runway in use and the visibility is observed related to these runways, the available visibility values for each runway should be reported, and the runways to which the values refer should be indicated.

4.6.10	Recommendation.— In reports in the METAR/SPECI code forms, when the visibility is not the same in different directions:

a)	the lowest visibility should be reported;

b)	when the visibility in one or more directions is more than 50 per cent above the lowest visibility, the lowest visibility observed should be reported and its general direction in relation to the site of the meteorological station indicated by reference to one of the eight points of the compass. If the lowest visibility is observed in more than one direction, then the most operationally significant direction should be reported;

c)	directional variations in visibility should be reported when the lowest visibility is less than 1 500 m and the visibility in another direction is more than 5 000 m. Where such variations in visibility are observed in more than one direction, then the most operationally significant direction should be reported; and

d)	when the visibility is fluctuating rapidly, and significant directional variations cannot be given, the lowest visibility should be reported, with no indication of direction.

4.7 Observing and reporting of

runway visual range

.

Note.— Guidance on the subject of runway visual range is contained in the ICAO Manual of Runway Visual Range Observing and Reporting Practices (Doc 9328).

4.7.1 Runway visual range as defined in Chapter 1 shall be observed on all runways intended for Category II and Category III instrument approach and landing operations.

4.7.2 Recommendation.— Runway visual range as defined in Chapter 1 should be observed on all runways intended for use during periods of reduced visibility, including:

a)	precision approach runways intended for Category I instrument approach and landing operations;

b)	runways used for take-off and having high-intensity edge lights and/or centre line lights.

Note.— Precision approach runways are defined in Annex 14, Volume I, Chapter 1, under "Instrument runway".

4.7.3 The runway visual range observations made in accordance with 4.7.1 and 4.7.2 shall be reported in metres in accordance with the reporting steps specified in 4.7.14 throughout periods when either the horizontal visibility or the runway visual range is less than 1 500 m.

Representativeness

4.7.4 Runway visual range observations shall be representative of:

a)	the touchdown zone of the runway intended for non-precision or Category I instrument approach and landing operations;

b)	the touchdown zone and the mid-point of the runway intended for Category II instrument approach and landing operations; and

c)	the touchdown zone, the mid-point and stop-end of the runway intended for Category III instrument and landing operations.

Siting

4.7.5	Recommendation. —Runway visual range should be observed at a height of approximately 2.5 m (7.5 ft).

4.7.6 Recommendation.— Runway visual range should be observed at a lateral distance from the runway centre line of not more than 120 m. The site for observations to be representative of the touchdown zone should be located about 300 m along the runway from the threshold. The sites for observations to be representative of the mid-point and stop-end of the runway should be located at a distance of 1 000 to 1 500 m along the runway from the threshold and at a distance of about 300 m from the other end of the runway. The exact position of these sites and, if necessary, additional sites should be decided after considering aeronautical, meteorological and climatological factors such as long runways, swamps and other fog-prone areas.

Instrumented systems

4.7.7 Instrumented systems based on transmissometers or forward-scatter meters shall be used to assess runway visual range on runways intended for Category II and III instrument approach and landing operations.

4.7.8 Recommendation. — Instrumented systems based on transmissometers or forward-scatter meters should be used to assess runway visual range on runways intended for Category I instrument approach and landing operations.

Note.— As accuracy can vary from one instrument design to another, performance characteristics are to be checked before selecting an instrument for assessing RVR. The calibration of a forward-scatter meter has to be traceable and verifiable to a transmissometer standard, the accuracy of which has been verified over the intended operational range. Guidance on the use of transmissometers and forward-scatter meters in instrumented RVR systems is given in the Manual of Runway Visual Range Observing and Reporting Practices (Doc 9328).

Displays

4.7.9 Where runway visual range is determined by instrumented systems, one display or more if required, shall be located in the meteorological station with corresponding displays, in the appropriate air traffic services units. The displays in the meteorological station and in the air traffic services units shall be connected to the same measuring device(s), and where separate sensors are required as specified in 4.7.6, the displays shall be clearly marked to identify the runway and section of runway monitored by each sensor.

4.7.10 Recommendation.— Where runway visual range is determined by human observers, runway visual range should be reported to the appropriate local air traffic services units, whenever there is a change in the value to be reported in accordance with the reporting scale (except where the provisions of 4.3.2 a) or b) apply). The transmission of such reports should normally be completed within 15 seconds after the termination of the observation.

Averaging

4.7.11 Where instrumented systems are used for the assessment of runway visual range, their output shall be updated at least every 60 seconds to permit the provision of current, representative values. The averaging period for runway visual range values shall be:

a)	1 minute for local routine and special reports and for runway visual range displays in air traffic services units; and

b)	10 minutes for reports in the METAR/SPECI code forms except when the 10-minute period immediately preceding the observation includes a marked discontinuity in runway visual range values, only those values occurring after the discontinuity shall be used for obtaining mean values .

Note.— A marked discontinuity occurs when there is an abrupt and sustained change in runway visual range, lasting at least 2 minutes, which reaches or passes through criteria for the issuance of special reports in the SPECI code form given in 4.3.4 f).

Light intensity

4.7.12 Recommendation.— When instrumented systems are used for the assessment of runway visual range, computations should be made separately for each available runway. Whatever intensities are used, RVR should not be computed for a light intensity of 3 per cent or less of the maximum light intensity available on a runway. The light intensity to be used for the computation should be:

a)	for a runway with the lights switched on, the light intensity actually in use on that runway;

b)	for a runway with lights switched off (or at the lowest setting pending the resumption of operations), the optimum light intensity that would be appropriate for operational use in the prevailing conditions.

In reports in the METAR/SPECI code forms, the runway visual range should be based on the same light intensity settings as those appropriate for use during take-off and landing at the time the report is made, but excluding any temporary changes in the light intensity settings.

Note.— Guidance on the conversion of instrumented readings into runway visual range is given in Attachment D.

Status

4.7.13 The units providing air traffic service and aeronautical information service for an aerodrome shall be kept informed without delay of changes in the serviceability status of the runway visual range observing system.

Reporting

4.7.14 In local routine and special reports and in reports in the METAR/SPECI code forms, the reporting scale shall consist of increments of 25 m for runway visual range below 400 m, increments of 50 m for runway visual range between 400 m and 800 m and increments of 100 m for runway visual range above 800 m. Any observed value which does not fit the reporting scale in use shall be rounded down to the nearest lower step in the scale.

4.7.15 Recommendation.— Fifty metres should be considered the lower limit and 2 000 metres the upper limit for runway visual range. Outside of these limits local routine and special reports and reports in the METAR/SPECI code forms should merely indicate that the runway visual range is less than 50 m or more than 2 000 m.

4.7.16	In local routine and special reports and in reports in the METAR/SPECI code forms:

a)	when runway visual range is above the maximum value that can be determined by the system in use, it shall be reported using the abbreviation "ABV" in local routine and special reports and the abbreviation "P" in reports in the METAR/SPECI code forms, followed by the maximum value that can be determined by the system; and

b)	when the runway visual range is below the minimum value that can be determined by the system in use, it shall be reported using the abbreviation "BLW" in local routine and special reports and the abbreviation "M" in reports in the METAR/SPECI code forms followed by the minimum value that can be determined by that system.

4.7.17 In local routine and special reports :

a)	the units of measurement used shall be included.

b)	if runway visual range is observed from one location along the runway, i.e. the touchdown zone, it shall be included without any indication of location;

c)	if the runway visual range is observed from more than one location along the runway, the value representative of the touchdown zone shall be reported first, followed by the values representative of the mid-point and stop-end and the locations for which these values are representative shall be indicated ; and

d)	when there is more than one runway in use, the available runway visual range values for each runway shall be reported and the runways to which the values refer shall be indicated .

4.7.18 In reports in the METAR/SPECI code forms:

a)	only the value representative of the touchdown zone shall be reported and no indication of location on the runway shall be included;

b)	where there is more than one runway available for landing, touchdown zone runway visual range values shall be included for all such runways and the runways to which the values refer shall be indicated.

4.7.19 Recommendation. — In reports in the METAR/SPECI code forms, when instrumented systems are used for the assessment of runway visual range, the variations in runway visual range during the 10-minute period immediately preceding the observation should be included as follows:

a)	if the runway visual range values during the 10-minute period have shown a distinct tendency, such that the mean during the first 5 minutes varies by 100 m or more from the mean during the second 5 minutes of the period, this should be indicated. When the variation of the runway visual range values shows an upward or downward tendency this should be indicated by the abbreviation "U" or "D" respectively. In circumstances when actual fluctuations during the 10-minute period show no distinct tendency this should be indicated using the abbreviation "N". When indications of tendency are not available, no abbreviations should be included; and

b)	if the one-minute runway visual range values during the 10-minute period vary from the mean value by more than 50 m or more than 20 per cent of the mean value, whichever is greater, the one-minute mean minimum and the one-minute mean maximum values should be reported instead of the 10-minute mean value. If the 10-minute period immediately preceding the observation includes a marked discontinuity in runway visual range values, only those values occurring after the discontinuity should be used to obtain variations.

Note.— A marked discontinuity occurs when there is an abrupt and sustained change in runway visual range, lasting at least 2 minutes, which reaches or passes through criteria for the issuance of special reports in the SPECI code form given in 4.3.4 f).

4.8 Observing and reporting of
present weather

4.8.1 The present weather occurring at the aerodrome and/or its vicinity shall be observed and this shall be reported as necessary.

Representativeness

4.8.2	Recommendation.— When local routine and special reports are used for departing aircraft, the present weather information should be representative of the take-off areas; when local routine and special reports are used for arriving aircraft, the present weather information should be representative of the landing area.

4.8.3	Recommendation.— For reports in the METAR/SPECI code forms, the present weather information should be representative of the aerodrome and its vicinity.

Manual insertion

4.8.4 Recommendation.— Where observations are made using automatic observing equipment, provision should be made for manual insertion in the corresponding displays of those present weather elements which cannot be determined adequately by that equipment.

Siting

4.8.5	Recommendation. — When instrumented systems are used for observing present weather phenomena listed under 4.8.8 and 4.8.9, representative information should be obtained by the use of sensors appropriately sited.

Displays

4.8.6	Recommendation. — When instrumented systems are used for observing present weather phenomena listed in 4.8.8 and 4.8.9, appropriate displays should be located in the meteorological station with corresponding displays in the appropriate air traffic services units.

Reporting

4.8.7 In local routine and special reports and in reports in the METAR/SPECI code forms, present weather phenomena shall be reported in terms of type and characteristics and qualified with respect to intensity or proximity to the aerodrome, as appropriate.

4.8.8 Recommendation.— In local routine and special reports and in reports in the METAR/SPECI code forms, the types of present weather phenomena which should be reported, their respective abbreviations and relevant criteria for their reporting of significance to aviation are as follows:

a)	Precipitation

Drizzle	DZ

Rain	RA

Snow	SN

Snow grains	SG

Ice pellets	PL

Ice crystals (very small ice crystals	IC

in suspension, also known as

diamond dust)

—	Reported only when associated

visibility is 5 000 m or less.

Hail	GR

—	Reported when diameter of largest

hailstones is 5 mm or more.

Small hail and/or snow pellets	GS

—	Reported when diameter of largest

hailstones is less than 5 mm.

b)	Obscurations (hydrometeors)

Fog	FG

—	Reported when visibility is less

than 1 000 m, except when

qualified by "MI", "BC", "PR"

or "VC" (see 4.8.5 and 4.8.6).

Mist	BR

—	Reported when visibility is at least

1 000 m but not more than 5 000 m.

c)	Obscurations (lithometeors)

The following should be used only when the obscuration consists predominantly of lithometeors and the visibility is 5 000 m or less except "SA" when qualified by "DR" (see 4.8.5) and volcanic ash.

Sand	SA

Dust (widespread)	DU

Haze	HZ

Smoke	FU

Volcanic ash	VA

d)	Other phenomena

Dust/sand whirls (dust devils)	PO

Squall	SQ

Funnel cloud (tornado or	FC

waterspout)

Duststorm	DS

Sandstorm	SS

4.8.9 Recommendation.— In local routine and special reports and in reports in the METAR/SPECI code forms, the characteristics of the present weather phenomena which should be reported, as necessary, and their respective abbreviations are as follows:

Thunderstorm	TS

—	Used to report a thunderstorm with rain "TSRA", snow "TSSN", hail "TSGR" or small hail and/or snow pellets "TSGS" or combinations thereof, for example, "TSRASN". When thunder is heard or lightning seen or detected within 20 km of the aerodrome during the 10-minute period preceding the time of observation but no precipitation is observed at the aerodrome, the abbreviation "TS" should be used without qualification.

Shower	SH

—	Used to report showers of rain "SHRA", snow "SHSN", hail "SHGR", small hail and/or snow pellets "SHGS", or combinations thereof, for example "SHRASN". Showers observed in the vicinity of the aerodrome (see 4.8.6) should be reported as "VCSH" without qualification regarding type or intensity of precipitation.

Freezing (supercooled water droplets or	FZ

precipitation, used only with FG, DZ

and RA)

Blowing	BL

—	Used to report DU, SA or SN raised by the wind to a height of 2 m (6 ft) or more above the ground; in the case of snow, also used to report snow falling from a cloud and mixed with snow raised by the wind from the ground.

Low drifting (used with DU, SA or SN raised	DR

by the wind to less than 2 m (6 ft) above

ground level)

Shallow (less than 2 m (6 ft) above ground	MI

level)

Patches (fog patches randomly covering the	BC

aerodrome)

Partial (a substantial part of the aerodrome	PR

covered by fog while the remainder

is clear)

4.8.10 Recommendation.— In local routine and special reports and in reports in the METAR/SPECI code forms, the relevant intensity or, as appropriate, the proximity to the aerodrome of the reported present weather phenomena should be indicated as follows:

(

local routine

and special reports)	(METAR/SPECI)

Light	FBL	–

Moderate	MOD	(no indication)

Heavy	HVY	+

—	Used only with DZ, RA, SN, SG and PL (or in combinations involving these present weather types; in these cases intensity refers to precipitation in accordance with 4.8.7); DS; and SS in the cases of DS and SS only moderate and heavy intensities to be indicated).

Vicinity	VC

—	Not at the aerodrome but not further away than approximately 8 km from the aero-
drome perimeter and used only in reports in the METAR/SPECI code forms with DS, SS, FG, FC, SH, PO, BLDU, BLSA, and BLSN when not reported under 4.8.5.

4.8.11 Recommendation.— In local routine and special reports and in reports in the METAR/SPECI code forms, one or more up to a maximum of three of the present weather abbreviations given in 4.8.4 and 4.8.5 should be used, as necessary, together with an indication, where appropriate, of the characteristics and intensity or proximity to the aerodrome, so as to convey a complete description of the present weather of significance to flight operations at the aerodrome and its vicinity. In reporting this information, the indication of intensity or proximity as appropriate, should be reported first followed respectively by the characteristics and the type of weather phenomena. Where two different types of weather are observed, they should be reported in two separate groups, where the intensity or proximity indicator refers to the weather phenomenon which follows the indicator. However, different types of precipitation occurring at the time of observation should be reported as one single group with the dominant type of precipitation reported first and preceded by only one intensity qualifier which refers to the intensity of the total precipitation.

4.9 Observing and reporting of cloud or vertical visibility

4.9.1 Cloud amount, cloud type and height of cloud base shall be observed, and reported as necessary to describe the cloud distribution of operational significance, in accordance with 4.9.7. When the sky is obscured, vertical visibility shall be observed in lieu of cloud amount, cloud type and height of cloud base. The height of cloud base and vertical visibility shall be reported in metres (feet).

Representativeness

4.9.2 Recommendation.— Cloud observations for local routine and special reports should be representative of the approach area or, in the case of aerodromes with precision approach runways, of the middle marker site of the instrument landing system.

Note.— Specifications concerning the middle marker site of an instrument landing system are given in Annex 10, Volume I, Chapter 3 and Attachment C, Table C-5.

4.9.3	Recommendation. — Cloud observations made for reports in the METAR/SPECI code forms should be representative of the aerodrome and its vicinity.

Manual insertion

4.9.4 Recommendation.— Where observations of the height of cloud base are made using automatic observing equipment , provision should be made for manual insertion of cloud amounts and, where appropriate, cloud type, together with the heights of those layers or masses not directly measurable by that equipment.

Siting

4.9.5	Recommendation. — When instrumented systems are used for the measurement of the height of cloud base, representative observations should be obtained by the use of sensors appropriately sited. Sensors for height of cloud base observations for local routine and special reports should be sited to give the best practicable indications of the height of cloud base at the middle marker site of the instrument landing system or, at aerodromes where a middle marker beacon is not used, at a distance of 900 to 1 200 m (3 000 to 4 000 ft) from the landing threshold at the approach end of the runway.

Displays

4.9.6	Recommendation. —When instrumented systems are used for the measurement of the height of cloud base, appropriate displays should be located in the meteorological station with corresponding displays in the appropriate air traffic services units.

Reference level

4.9.7 Recommendation.— The height of the base of cloud should normally be reported above aerodrome elevation. When a precision approach runway is in use which has a threshold elevation 15 m (50 ft) or more below the aerodrome elevation, local arrangements should be made in order that the height of clouds reported to arriving aircraft should refer to the threshold elevation. In the case of reports from off-
shore structures the height of the base of cloud should be given above mean sea level.

Reporting

4.9.8	In local routine and special reports and in reports in the METAR/SPECI code forms, only clouds of operational significance, i.e. cumulonimbus clouds and clouds with heights of their bases below 1 500 m (5 000 ft) or below the highest minimum sector altitude, whichever is greater, shall be reported.

4.9.9	In local routine and special reports and in reports in the METAR/SPECI code forms,

cc

a)	cloud amount shall be reported using the abbreviations "FEW" (1 to 2 oktas), "SCT" (3 to 4 oktas), "BKN" (5 to 7 oktas) or "OVC" (8 oktas);

b)	cumulonimbus clouds shall be indicated as "CB";

c)	the height of cloud base and vertical visibility shall be reported in steps of 30 m (100 ft) up to 3 000 m (10 000 ft) and in steps of 300 m (1 000 ft) above 3 000 m (10 000 ft);

d)	if there are no clouds and no restriction on vertical visibility and the abbreviation "CAVOK" is not appropriate, the abbreviation "SKC" shall be used;

e)	if there are no clouds of operational significance and no restriction on vertical visibility and the abbreviations "CAVOK" and "SKC" are not appropriate, the abbreviation "NSC" shall be used ;

f)	when several layers or masses of cloud of operational significance are observed, their amount and height of cloud base shall be reported in the following order:

1)	the lowest layer or mass, regardless of amount to be reported as FEW, SCT, BKN or OVC as appropriate;

2)	the next layer or mass, covering more than 2/8 to be reported as SCT, BKN or OVC as appropriate;

3)	the next higher layer or mass, covering more than 4/8 to be reported as BKN or OVC as appropriate;

4)	cumulonimbus , whenever observed and not reported in a) to c) above.

g)	when the cloud base is diffuse or ragged or fluctuating rapidly, the minimum height of the cloud, or cloud fragments, shall be reported.

4.9.10	In local routine and special reports,

a)	the units of measurement used for the height of cloud base and vertical visibility shall be indicated;

b)	when there is more than one runway in use and cloud heights are observed by instruments for these runways, the available cloud height values for each runway shall be reported and the runways to which the values refer shall be indicated;

c)	towering cumulus clouds shall be indicated as "TCU".

Note.— Towering cumulus indicates cumulus congestus clouds of great vertical extent.

4.10 Observing and reporting of air

temperature and dew-point temperature

4.10.1 The air temperature and the dew-point temperature shall be measured and reported to the nearest whole degree Celsius, with observed values involving 0.5 C rounded up to the next higher whole degree Celsius.

Representativeness

4.10.2 Recommendation.— Observations of air temperature and dew-point temperature for local routine and special reports and reports in the METAR/SPECI code forms should be representative of the whole runway complex.

Reporting

4.10.3 In local routine and special reports, a temperature below 0 C shall be preceded by "MS" .

4.10.4	In reports in the METAR/SPECI code forms, a temperature below 0 C shall be preceded by "M".

4.11 Observing and reporting of

pressure values

4.11.1 The atmospheric pressure shall be measured and QNH and, QFE values shall be computed in tenths of a hectopascal. QNH, and QFE when required in accordance with 4.11.4, shall be reported in hectopascals, using four digits, rounded down to the nearest lower whole hectopascal.

Display

4.11.2 When automated systems are used for the measurement of pressure, QNH/QFE displays relating to the barometer shall be located in the meteorological station with corresponding displays in the appropriate air traffic services units. When QFE values are displayed for more than one runway, as specified in 4.11.3, the displays shall be clearly marked to identify the runway to which the QFE value displayed refers.

Reference level

4.11.3 Recommendation.— The reference level for the computation of QFE should be the aerodrome elevation. For non-precision approach runways, the thresholds of which are 2 m (7 ft) or more below the aerodrome elevation, and for precision approach runways, the QFE, if required, should refer to

the relevant threshold elevation.

Reporting

4.11.4 In local routine and special reports:

a)	QNH shall be included ;

b)	QFE shall be included either on request or, if so agreed locally between the meteorological and air traffic services authorities and operators concerned, on a regular basis;

c)	the units of measurement used for QNH and QFE values shall be included; and .

d)	If QFE values are required for more than one runway, the required QFE values for each runway shall be reported and the runways to which the values refer shall be indicated.

4.11.5 In reports in the METAR/SPECI code forms only QNH values shall be included be .

4.12 Observing and reporting of

supplementary information

4.12.1 Recommendation.— Observations made at aerodromes should include the available supplementary information concerning significant meteorological conditions, particularly those in the approach and climb-out areas . Where practicable, the information should identify the location, of the meteorological condition.

Manual insertion

4.12.2 Recommendation.— Where observations are made using automatic observing equipment, provision should be made for manual insertion of information concerning significant meteorological conditions which cannot be determined adequately by that equipment.

Reporting

4.12.3 Recommendation.— In local routine and special reports, and in reports in the METAR/SPECI code forms, the following recent weather phenomena , i.e. weather phenomena observed at the aerodrome during the period since the last issued routine report or last hour, whichever is the shorter, but not at the time of observation, should be reported, up to a maximum of three groups, in the supplementary information:

—	freezing precipitation	REFZDZ, REFZRA

—	moderate or heavy precipitation

(including showers thereof)	REDZ, RERA, RESN, RESG, REGR, REGS, REPL, RESHRA, RESHSN, RESHSG, RESHGR, RESHGS, REIC

—	moderate or heavy blowing snow

REBLSN

—	duststorm or sandstorm	REDS, RESS

—	thunderstorm	RETS

—	funnel cloud (tornado or water spout)	REFC

—	volcanic ash	REVA.

4.12.4 Recommendation.— In local routine and special reports, the following significant meteorological conditions should be reported in supplementary information:

—	cumulonimbus clouds	CB

—	thunderstorm	TS

—	moderate or severe turbulence	MOD TURB, SEV TURB

—	wind shear	WS

—	hail	GR

—	severe squall line	SEV SQL

—	moderate or severe icing	MOD ICE, SEV ICE

—	freezing precipitation	FZDZ, FZRA

—	severe mountain waves	SEV MTW

—	duststorm or sandstorm	DS, SS

—	blowing snow	BLSN

—	funnel cloud (tornado or water spout)	FC.

The location of the condition should be indicated.

Where necessary, additional information should be included using abbreviated plain language.

4.12.5	Recommendation.— In reports in the METAR/SPECI code forms, where local circumstances so warrant, information on wind shear should be added .

Note.— The local circumstances referred to in 4.12.5 include, but are not necessarily limited to, wind shear of a non-transitory nature such as might be associated with low-level temperature inversions or local topography.

4.12.6 Recommendation.— In reports in the METAR/SPECI code forms, the following information should be included in the supplementary information, in accordance with regional air navigation agreement:

a)	information on sea-surface temperature and the state of the sea from aeronautical meteorological stations established on off-
shore structures in support of helicopter operations ; and

Note.— The state of the sea is specified in WMO Publication No. 306, Manual on Codes, Volume I.1, Part A — Alphanumeric Codes, Code Table 3700.

b)	information on the state of the runway provided by the appropriate airport authority .

Note.— The state of the runway is specified in WMO Publication No. 306, Manual on Codes, Volume I.1, Part A — Alphanumeric Codes, Code Tables 0370, 0519, 0919 and 1079.

Editorial Note: — New text.

4.13 Reporting of meteorological information

from automated meteorological observing systems

4.13.1 Recommendation. — Where automated meteorological observing systems are used, during non-operational hours of the aerodrome, reports from automated meteorological observing systems should be issued in the METAR/SPECI code forms and these reports should be identified with the word "AUTO". Routine and special reports in the METAR/SPECI codes issued during the two-hour period prior to the aerodrome resuming operations in accordance with 4.2.3 and 4.3.3 should be similar to those issued during the operational hours of the aerodrome.

Reporting

4.13.2 Recommendation. — In automated reports in the METAR/SPECI code forms, surface wind, runway visual range, air temperature and dew-point temperature, and pressure values should be reported in accordance with provisions relevant to reports in the METAR/SPECI code forms included in Sections 4.5, 4.7, 4.10 and 4.11, respectively.

4.13.3 Recommendation. — In automated reports in the METAR/SPECI code forms, visibility should be reported as the minimum value of the visibility readings available from all visibility sensors available at the aerodrome.

4.13.4 Recommendation. — In automated reports in the METAR/SPECI code forms, present weather should be reported in accordance with provisions relevant to reports in the METAR/SPECI code forms included in Section 4.8.

4.13.5 Recommendation. — In automated reports in the METAR/SPECI code forms, cloud or vertical visibility should be reported in accordance with provisions relevant to reports in the METAR/SPECI code forms included in Section 4.9.

4.13.6 Recommendation. — In automated reports in the METAR/SPECI code forms, supplementary information should not be included.

Editorial Note: — End of new text.

4.14 Contents of reports

4.14.1 Local routine and special reports and routine and special reports in the METAR/SPECI code forms shall contain the following information in the order indicated, except that local special reports need not contain information as provided for under 4.3.3:

a)	identification of the type of report;

b)	location indicator;

c)	time of the observation;

d)	surface wind direction and speed;

e)	visibility;

f)	runway visual range, when applicable;

g)	present weather;

h)	cloud amount, cloud type (only for cumulonimbus and, in local routine and special reports, for towering cumulus clouds ) and height of cloud base;

i)	air temperature and dew-point temperature;

j)	QNH and, when applicable, QFE (QFE included only in local routine and special reports ;

Note .— The location indicators referred to under b) and their significations are published in ICAO Doc 7910 — Location Indicators.

Note 2.— For explanation of towering cumulus see note following 4.9.9.

4.14.2 Recommendation. — In addition to elements listed under 4.13.1 a) to j), local routine and special reports and routine and special reports in the METAR/SPECI code forms should contain supplementary information in accordance with 4.12 to be included as the last element of the report.

4.14.3 When the following conditions obtain simultaneously at the time of observation:

a)	visibility, 10 km or more;

b)	no cloud below 1 500 m (5 000 ft) or below the highest minimum sector altitude, whichever is greater, and no cumulonimbus;

c)	no weather of significance to aviation as given in 4.8.4 and 4.8.5;

information on visibility, runway visual range, present weather and cloud amount, type and height shall be replaced in all meteorological reports by the term "CAVOK".

Editorial Note: — Renumber Section 4.14 to read 4.15.

CHAPTER 6. FORECASTS

• • • • •

6.2 Aerodrome forecasts

• • • • •

6.2.3 Aerodrome forecasts and amendments thereto shall be issued as TAF forecasts, in accordance with the template shown in Appendix 4 and exchanged in the TAF or BUFR code forms and include the following information in the order indicated:

a)	identification of the type of forecast;

b)	location indicator;

c)	date and time of origin of forecast;

d)	date and period of validity of forecast;

e)	surface wind;

f)	visibility;

g)	weather;

h)	cloud; and

i)	expected significant changes to one or more of these elements during the period of validity.

Additional elements shall be included in aerodrome forecasts in accordance with regional air navigation agreement.

Note 1.— The TAF and BUFR code forms are contained in WMO Publication No. 306, Manual on Codes, Volume I.1, Part A — Alphanumeric Codes and Volume I.2, Part B — Binary Codes, respectively.

Note 2.— Examples of TAF forecasts are given in Appendix 4.

6.2.4 Meteorological offices preparing aerodrome forecasts shall keep the forecasts under continuous review and, when necessary, shall issue amendments promptly. The length of the forecast messages and the number of changes indicated in the forecast shall be kept to a minimum.

6.2.5	Aerodrome forecasts that cannot be kept under continuous review due to the absence of reports in the METAR/SPECI code forms for that aerodrome, shall be cancelled.

Note. — Reports in the METAR/SPECI code forms identified with "AUTO" cannot at the present time be used for review of aerodrome forecasts.

Editorial Note: — Renumber Paragraphs 6.2.5 to 6.2.17 to read 6.2.6 to 6.2.18.

APPENDIX 2 TECHNICAL SPECIFICATIONS FOR LOCAL ROUTINE REPORTS, LOCAL SPECIAL REPORTS AND REPORTS IN THE METAR/SPECI CODE FORMS

(See Chapter 4 of this Annex)

Table 1. Template for the local routine (MET REPORT) and local special (SPECIAL) report

Key:

M	=	inclusion mandatory, part of every message

C	=	inclusion conditional, dependent on meteorological conditions

O	=	inclusion optional

Note 1. —	The ranges and resolutions for the numerical elements included in the local routine and special reports are shown in Table 4 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 4	Detailed content	Template(s)	Examples

• • • • •

Present weather (C)9,10	Intensity or proximity of present weather (C)11	FBL or MOD or HVY	—	CAVOK
Characteristics and type of present weather (M)12	DZ or RA or SN or SG or PL or or DS or SS or TSRA or TSSN or SHRA or SHSN or SHGR or SHGS or FZRA or FZDZ	IC or GR or GS or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or TSGR or TSGS or FZFG or BLSN or BLSA or BLDU or DRSN or DRSA or DRDU or MIFG or BCFG or PRFG

MOD RA;	HZ;

HVY TSRA;	FG;

HVY DZ;	VA;

FBL SN;	MIFG;

HVY TSRASN;

FBL SNRA;

FBL DZ FG;

HVY SHSN BLSN;

• • • • •

Supplementary information (C)9	Significant met. phenomena (C)9	CB or TS or MOD TURB or SEV TURB or WS or GR or SEV SQL or MOD ICE or SEV ICE or FZDZ or FZRA or SEV MTW or SS or DS or BLSN or FC15	FC IN APCH;

WS IN APCH WIND AT 60M 360/50KMH;

WS RWY 12;
Location of the phenomenon (C)9	IN APCH or IN CLIMB-OUT or RWYnnn

Recent weather (C)9	REFZDZ or REFZRA or REDZ or RE[SH]RA or RE[SH]SN or RE[SH]SG or REPL or REIC or RE[SH]GR or RE[SH]GS or REBLSN or RESS or REDS or RETS or REFC or REVA	REFZRA;

CB IN CLIMB-OUT RETS;

Trend forecast (O)16	Name of the element (M)	TREND
Change indicator (M)	NOSIG	BECMG or TEMPO	TREND NOSIG;	TREND BECMG FEW 600M;

(TREND BECMG FEW 2000FT);
Period of change (C)9	FMnnnn and/or TLnnnn

or

ATnnnn
Wind (C)9	nnn/[ABV]nn[n]KMH [MAX[ABV]nn[n]] or

nnn/[ABV]nnKT [MAX[ABV]nn]	TREND TEMPO 250/70KMH MAX 100;

(TREND TEMPO 250/35KT MAX 50);
Visibility (C)9	VIS nnnnM or

VIS nnKM	CAVOK	TREND BECMG AT1800 VIS 10KM NSW;

TREND BECMG TL1700 VIS 800M FG;

TREND BECMG FM1030 TL1130 CAVOK;
Weather phenomenon: intensity (C)11	FBL or

MOD or

HVY	—	NSW	TREND TEMPO TL1200 VIS 600M BECMG AT1200 VIS 8KM NSW NSC;
Weather phenomenon: characteristics and type (C)9, 10, 12	DZ or RA or SN or SG or PL or or DS or SS or TSRA or TSSN or SHRA or SHSN or SHGR or SHGS or FZRA or FZDZ	IC or GR or GS or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or TSGR or TSGS or FZFG or BLSN or BLSA or BLDU or DRSN or DRSA or DRDU or MIFG or BCFG or PRFG	TREND TEMPO FM0300 TL0430 MOD FZRA;

TREND BECMG FM1900 VIS 500M HVY SNRA;

TREND BECMG FM1100 MOD SN TEMPO FM1130 BLSN;
Cloud amount and vertical visibility (C)9	FEW or SCT or BKN or OVC	OBSC	SKC or NSC	TREND BECMG AT1130 OVC 300M;

(TREND BECMG AT1130 OVC 1000FT);

Cloud type (C)9	CB	—	TREND TEMPO TL1530 HVY SHRA BKN CB 360M;

(TREND TEMPO TL1530 HVY SHRA BKN CB 1200FT);
Height of base or the value of vertical visibility (C)9	nnnnM or nnnnFT	[VER VIS nnnM or VER VIS nnnnFT]

Notes. —

1.	Fictitious location;

2.	Optional values for one or more runways;

3.	Optional values for one or more sections of the runway;

4.	To be included if the maximum is exceeding the mean speed by 20 km/h (10 kt);

5.	To be included if the directional variations ≥ 60°but < 180 and the wind speed ≥ 6 km/h (3 kt);

6.	To be included if visibility or RVR < 1500 m;

7.	To be included if more than one runway in use;

8.	To be included if RVR is observed from more than one location along the runway;

9.	To be included whenever applicable;

10.	One or more, up to a maximum of three groups;

11.	To be included whenever applicable;

12.	Precipitation types DZ, RA, SN, SG, PL, IC, GR and GS may be combined, where appropriate. Only moderate or heavy precipitation to be indicated in trend forecasts;

13.	Up to four cloud layers;

14.	Optional element;

15.	Any of the phenomena, or combinations thereof. Abbreviated plain language to be used to amplify the phenomena, as necessary.

16.	To be included subject to Regional Air Navigation Agreement;

• • • • •

Table 2. Template for reports in the METAR/SPECI code forms

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 reports in the METAR/SPECI code forms are shown in Table 5 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 4	Detailed content	Template(s)	Examples
Identification of the type of report (M)	Type of the report (M)	METAR, METAR COR, SPECI or SPECI COR	METAR;

METAR COR;

SPECI
Location indicator (M)	ICAO location indicator (M)	nnnn	YUDO1
Time of the observation (M)	Date and time of the observation in UTC (M)	nnnnnnZ	221630Z
Identification of a missing report (C)	Missing report identifier (C)	NIL	NIL
END OF THE METAR REPORT IF THE REPORT IS MISSING
Identification of reports from automated meteoro- logical observing systems (C)17	Identification of the report	AUTO	AUTO
Present weather (C)9,10	Intensity or proximity of present weather (C)11	- or+

—	VC	C

A

V

O

K

Characteristics and type of present weather (M)12	DZ or RA or SN or SG or PL or or DS or SS or TSRA or TSSN or SHRA or SHSN or SHGR or SHGS or FZRA or FZDZ

IC or GR or GS or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or TSGR or TSGS or FZFG or BLSN or BLSA or BLDU or DRSN or DRSA or DRDU or MIFG or BCFG or PRFG	FG or PO or

FC or

DS or

SS or

SH or

BLSN or

BLSA

or

BLDU	RA;	HZ;	VCFG;

+TSRA;	FG;	VCSH;

+DZ;	VA;

-SN;	MIFG;	VCBLSA;

+TSRASN;

-SNRA;

-DZ FG;

+SHSN BLSN;
Cloud (M)13	Cloud amount and

height of base or

vertical visibility (M)	FEWnnn or

SCTnnn

or

BKNnnn or

OVCnnn	VVnnn or

VV///	SKC

or

NSC	FEW015;	VV005;	SKC;

OVC030;	VV///;	NSC;

SCT010 OVC020;
Cloud type (C)9	CB

—	BKN009;

SCT008 BKN025CB;

• • • • •

Supplementary information (C)9	Recent weather (C)9, 10	REFZDZ or REFZRA or REDZ or RE[SH]RA or RE[SH]SN or RE[SH]SG or RE[SH]PL or REIC or RE[SH]GR or RE[SH]GS or REBLSN or RESS or REDS or RETS or REFC or REVA	REFZRA;

RETS;
Wind shear (C)9	WS RWYnn[n] or WS ALL RWY	WS RWY03;

WS ALL RWY;
Sea-surface temperature and state of the sea (C)14	W[M]nn/Sn	W15/S2;
State

of the runway (C)14	Runway designator (M)	nn	SNOCLO	99421594;

SNOCLO;

14CLRD//
Runway deposits (M)	n or /	CLRD//
Extent of runway contamination (M)	n or /
Depth of deposit (M)	nn or //
Friction coefficient or braking action (M)	nn or //
Trend forecast (O)14	Change indicator (M)15	NOSIG

BECMG or TEMPO	NOSIG;	BECMG FEW020;
Period of change (C)9	FMnnnn and/or

TLnnnn

or

ATnnnn
Wind (C)9	nnn[P]nn[n][G[P]nn[n]]KMH

or

nnn[P]nn[G[P]nn]KT	TEMPO 25070G100KMH;

(TEMPO 25035G50KT);
Visibility (C)9	nnnn	C

A

V

O

K	BECMG FM1030 TL1130 CAVOK;

BECMG TL1700 0800 FG;
Weather phenomenon: intensity (C)11	-or+	—	N

S

W	BECMG AT1800 9000 NSW;

BECMG FM1900 0500 +SNRA;

BECMG FM1100 SN TEMPO FM1130 BLSN;

TEMPO FM0330 TL0430 FZRA;
Weather phenomenon: characteristics and type (C)9,10,12	DZ or RA or SN or SG or PL or DS or SS or TSRA or TSSN or SHRA or SHSN or SHGR or SHGS or FZRA or FZDZ

IC or GR or GS or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or TSGR or TSGS or FZFG or BLSN or BLSA or BLDU or DRSN or DRSA or DRDU or MIFG or BCFG or PRFG
Cloud amount and height of base or vertical visibility (C)9	FEWnnn or

SCTnnn

or

BKNnnn

or

OVCnnn	VVnnn or

VV///	S

K

C

or

N

S

C	TEMPO TL1200 0600 BECMG AT1200 8000 NSW NSC;

BECMG AT1130 OVC010;
Cloud type (C)9	CB	—	TEMPO TL1530 +SHRA BKN012CB;
Notes. —

1.	Fictitious location;

2..	To be included if the maximum is exceeding the mean speed by 20 km/h (10 kt);

3.	To be included if the directional variations ≥ 60°but < 180 and the wind speed > 6 km/h (3 kt);

4.	To be included if the visibility in one or more directions is more than 50 per cent above the minimum visibility;

5.	To be included if the minimum visibility is less than 1500 m and the visibility in another direction is more than 5000m;

6.	To be included if visibility or RVR < 1500 m; for up to a maximum of four runways;

7.	To be included if the one-minute RVR values during the 10-minute period immediately preceding the observation vary from the mean value more than 50 m or more than 20 per cent, whichever is greater; the one-minute mean minimum and the one-minute mean maximum values are reported (instead of the 10-minute mean value);

8.	To be included if the RVR values during the 10-minute period preceding the observation have shown a distinct tendency such that the mean RVR during the first 5 minutes varies by 100 m or more from the mean during the second 5 minutes of the period. No tendency indication where not available;

9.	To be included whenever applicable;

10.	One or more, up to a maximum of three, groups;

11.	To be included whenever applicable. No qualifier for moderate intensity ;

12.	Precipitation types DZ, RA, SN, SG, PL, IC, GR and GS may be combined, where appropriate. Only moderate or heavy precipitation to be indicated in trend forecasts;

13.	Up to four cloud layers;

14.	To be included subject to Regional Air Navigation Agreement;

15.	Number of change indicators to be kept to a minimum; normally not exceeding three groups;

16.	Followed by "NIL" for a missing report;

17.	Identification for reports from automated meteorological observing systems during non-operational hours of the aerodrome.

• • • • •

APPENDIX 4 TECHNICAL SPECIFICATIONS FOR AERODROME FORECASTS

IN THE TAF CODE FORM

(See Chapter 6 of this Annex)

Table 1. Template for aerodrome forecasts in the TAF code form

Key:	M	=	inclusion mandatory, part of every message

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

O	=	inclusion optional

Note.—	The ranges and resolutions for the numerical elements included in aerodrome forecasts in the TAF code form is shown in Table 3 of this appendix.

Note.—	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 report (M)	Type of the report (M)	TAF or TAF AMD or TAF COR	TAF;

TAF AMD;
Location indicator (M)	ICAO location indicator (M)	nnnn	YUDO1
Date and time of origin of forecast (M)	Date and time of the origin of the forecast in UTC (M)	nnnnnnZ	160000Z
Date and period of validity of forecast (M)	Date and period of the validity of the forecast in UTC (M)	nnnnnn	160624;

080918
Identification of a missing report (C)	Missing report identifier (C)	NIL or CNL	NIL;

CNL
END OF THE TAF FORECAST IF THE FORECAST IS MISSING OR CANCELLED

• • • • •

Weather (C)4, 5	Intensity of weather phenomena (C)6	- or +	—	C

A

V

O

K
Characteristics and type of weather phenomena (M) 7	DZ or RA or SN or SG or PL or DS or SS or TSRA or TSSN or or SHRA or SHSN or SHGR or SHGS or FZRA or FZDZ	IC or GR or GS or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or TSGR or TSGS or FZFG or BLSN or BLSA or BLDU or DRSN or DRSA or DRDU or MIFG or BCFG or

PRFG	RA;	HZ;

+TSRA;	FG;

-FZDZ;	PRFG;

+TSRASN;

SNRA FG;

• • • • •

Expected significant changes to one or more of the above elements during the period of validity (C)4, 10

• • • • •

Weather phenomenon: intensity (C)6	- or +	—	NSW	C

A

V

O

K	BECMG 1214 RA;
Weather phenomenon: characteristics and type

(C)4, 7, 10	DZ or RA or SN or SG or PL or DS or SS or TSRA or TSSN or SHRA or SHSN or SHPL or SHGR or SHGS or FZRA or FZDZ

IC or GR or GS or FG or BR or SA or DU or HZ or FU or VA or SQ or PO or FC or TS or TSGR or TSGS or FZFG or BLSN or BLSA or BLDU or DRSN or DRSA or DRDU or MIFG or BCFG or	TEMPO 0304 FZRA;

FM1030 SN TEMPO 1215 BLSN;

PROB40 TEMPO 0608 0500 FG;

• • • • •

Notes. —

1.	Fictitious location;

2.	To be included if the maximum is exceeding the mean speed by 20 km/h (10 kt);

3.	To be used only if the wind speed ≤ 6 km/h (3 kt);

4.	To be included whenever applicable;

5.	One or more, up to a maximum of three, groups;

6.	To be included whenever applicable. No qualifier for moderate intensity;

7.	Precipitation types DZ, RA, SN, SG, PL, IC, GR and GS may be combined, where appropriate. Only moderate or heavy precipitation should be indicated;

8.	Up to four cloud layers;

9.	To be included subject to Regional Air Navigation Agreement;

10.	To be included when a change in some or all of the elements forecast is expected to occur; may be placed after any element forecast, as appropriate; and

11.	Number of change indicators to be kept to a minimum; normally not exceeding five groups.

— — — — —

AMOSSG/3-SN No. 02

OF ANNEX 3 CONCERNING "PREVAILING VISIBILITY" FOR INCLUSION IN AMENDMENT 73

(applicable November 2004)

CHAPTER 1. DEFINITIONS

• • • • •

Prevailing visibility. The visibility value, observed in accordance with the definition of "visibility", which is reached or exceeded within at least half the horizon circle. The half horizon circle could comprize different contiguous or non-contiguous sectors.

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CHAPTER 4. METEOROLOGICAL OBSERVATIONS

AND REPORTS

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4.3 Special observations, special reports

and selected special reports

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4.3.4 Recommendation. — Special reports in the SPECI code form should be issued whenever changes in accordance with the following criteria occur:

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e)	when the prevailing visibility is improving and changes to or passes through one or more of the following values, or when the visibility is deteriorating and passes through one or more of the following values:

1) 800, 1 500 or 3 000 m;

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

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4.6 Observing and reporting of visibility

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4.6.9	Recommendation.— In reports in the METAR/SPECI code forms, when the visibility is not the same in different directions:

a)	the prevailing visibility should be reported;

b)	when the prevailing visibility is 5 000 m or less and the lowest visibility in one or more directions is less than 50 per cent of the prevailing visibility, the lowest visibility observed should also be reported and its general direction in relation to the site of the meteorological station indicated by reference to one of the eight points of the compass. If the lowest visibility is observed in more than one direction, then the most operationally significant direction should be reported; and

c)	when the visibility is fluctuating rapidly, and the prevailing visibility cannot be determined, only the lowest visibility should be reported, with no indication of direction.

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CHAPTER 6. FORECASTS

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6.2.3	Aerodrome forecasts and amendments thereto shall be issued as TAF forecasts, in accordance with the template shown in Appendix 4 and exchanged in the TAF or BUFR code forms and include the following information in the order indicated:

a)	identification of the type of forecast;

b)	location indicator;

c)	date and time of origin of forecast;

d)	date and period of validity of forecast;

e)	surface wind;

f)	visibility;

g)	weather;

h)	cloud; and

i)	expected significant changes to one or more of these elements during the period of validity.

Additional elements shall be included in aerodrome forecasts in accordance with regional air navigation agreement.

Note 1.— The TAF and BUFR code forms are contained in WMO Publication No. 306, Manual on Codes, Volume I.1, Part A — Alphanumeric Codes and Volume I.2, Part B — Binary Codes, respectively.

Note 2.— Examples of TAF forecasts are given in Appendix 4.

Note 3. - The visibility included in aerodrome forecasts refers to the forecast prevailing visibility.

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6.3.3	A trend-type landing forecast shall consist of a local routine or local special report; or a routine or special report in the METAR/SPECI code forms for an aerodrome to which is appended a concise statement of the expected trend of the meteorological conditions at the aerodrome. The period of validity of a trend-type landing forecast shall be 2 hours from the time of the report which forms part of the landing forecast. The trend- type landing forecast shall indicate significant changes in respect of one or more of the elements surface wind, visibility, weather and cloud. Only those elements shall be included for which significant change is expected. However, in the case of significant changes in respect of cloud, all cloud groups, including layers or masses not expected to change, shall be indicated. In the case of a significant change in visibility, the phenomenon causing the reduction of visibility shall also be indicated. When no change is expected to occur, this shall be indicated by the term "NOSIG".

Note. - The visibility included in trend-type landing forecasts refers to the forecast prevailing visibility.

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Editorial Note: — Consequential amendments to Annex 2 — Rules of the Air, and to the Procedures for Air Navigation Services — Rules of the Air and Air Traffic Services (PANS-RAC, Doc 4444) as follows:

ANNEX 2

RULES OF THE AIR

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CHAPTER 1. DEFINITIONS

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Ground visibility. The visibility at an aerodrome as reported by an accredited observer or by the aeronautical meteorological station.

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Editorial Note: — Add after the definition of visibility the following note:

Note 2. - The definition applies to the observations of visibility in local routine and special reports, to the observations of prevailing visibility reported in reports in the METAR/SPECI code forms and to the observations of ground visibility.

— — — — —

PROCEDURES FOR AIR NAVIGATION SERVICES

RULES OF THE AIR

AND

AIR TRAFFIC SERVICES (DOC 4444)

CHAPTER 1. DEFINITIONS

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Editorial Note: — Add after the definition of visibility the following note:

Note 2. - The definition applies to the observations of visibility in local routine and special reports, to the observations of prevailing visibility reported in reports in the METAR/SPECI code forms and to the observations of ground visibility.

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PART IX. AIR TRAFFIC SERVICES MESSAGES

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4.3 Flight information messages

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4.3.2	Messages containing meteorological information

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4.3.2.3.2	Visibility, including significant directional variations

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4.3.2.3.2.3	In meteorological reports disseminated beyond the aerodrome, the visibility shall be representative of the aerodrome and its vicinity. In the case of significant directional variations in visibility:

a)	the prevailing visibility shall be reported; and

b)	an additional value of the lowest visibility shall be given with an indication of the direction of observation.

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