"AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP AMOFSG AMOFSG 8 SN No 9 6 10 09"
AMOFSG/8-SN No. 9 6/10/09 AERODROME METEOROLOGICAL OBSERVATION AND FORECAST STUDY GROUP (AMOFSG) EIGHTH MEETING Melbourne, Australia, 15 to 18 February 2010 Agenda Item 5: Observing and forecasting at the aerodrome and in the terminal area 5.2: Aerodrome forecasts REPORT FROM AMOFSG/7 AD HOC TEAM ON THE ALIGNMENT OF ATTACHMENT B TO ANNEX 3 WITH THE TAF AMENDMENT CRITERIA (Presented by Bryan Boase, Rapporteur of AMOFSG/7 ad hoc group (2)) SUMMARY This study note highlights issues relating to the current operationally desirable accuracy for Aerodrome Forecasts (TAF). 1. INTRODUCTION 1.1 The group will recall previous discussions on this subject matter during AMOFSG/7 noted a need had been established to consider aligning the desirable accuracy of forecasts at aerodromes, contained in Attachment B to Annex 3 — Meteorological Service for International Air Navigation with the TAF amendment criteria to render any verification process more straightforward for those States wishing to do so. This need had also been established by the Air Navigation Commission (ANC) during the final review of Amendment 74 to Annex 3. The group agreed that, since the criteria given in Attachment B to Annex 3 cannot simply be scaled to fit the TAF amendment criteria, an ad hoc group should be established to consider the thresholds given and the desirable levels of accuracy for each threshold. 1.2 An ad hoc group consisting of Bryan (Rapporteur), Steve, Hervé, Colin, Bill and CM was created to consider the alignment of Attachment B to Annex 3 with the TAF amendment criteria and the updating of the criteria for precipitation forecasts. (11 pages) AMOFSG.8.SN.009.5.en.doc AMOFSG/8-SN No. 9 -2- 2. DISCUSSION 2.1 Bill provided a valuable starting point and “framework” within which to assess the proposal based on eight discussion points he had raised. Members of the ad hoc group were invited to make comment pertinent to each of the discussion points and provide any additional input they felt was relevant. These are provided below. 2.2 A summary of the proposed changes is presented in a tabular format (see attachment) that enables a comparison between the various issues under consideration. The issue of alignment with the known capabilities of the METAR / SPECI was also raised and as such, these are also presented in the table. 2.3 The discussion points with a précis of the responses from the group are as follows: Discussion Point 1: The desirable TAF performance requirements need to be based upon user validated criteria related to significant changes in weather conditions. It is recommended that any revised criteria be reviewed with an end user perspective. User consultation is seen as a fundamental philosophy that underpinning this whole process. Discussion Point 2: The desirable TAF performance should be defined in terms of the surface wind, visibility, weather and cloud. This was seen as a viable proposal but with due reference to point 3 below. Discussion Point 3: Temperature should be dropped from the list of operationally desirable accuracy of the TAF. It is neither a mandatory element nor is it widely included. As temperatures is included as an option parameter in the TAF (Annex 3, App 5, 1.2.5) and if used (by Regional Air Navigation Agreement) guidance as to the desirable accuracy is required. Further discussion as to the accuracy (maybe +2ºC instead of +1 ºC) and the form the temperature takes in the TAF (i.e. Max/Min or hourly temperatures) is required. Discussion Point 4: The desirable TAF accuracy must be developed in terms of the known capabilities of the METAR / SPECI. In other words, the criteria in Attachment B that relate to the TAF must be a subset of the criteria in Attachment A that relate to the METAR / SPECI. This approach was supported and it was also felt that even for those States that do not provide SPECI, that the SPECI criteria clearly establish what changes in weather are significant to operators. -3- AMOFSG/8-SN No. 9 Discussion Point 5: The desirable TAF accuracy performance as well as any TAF amendment criteria should also be a subset of the recommendations established for SPECI issuance. Details of the current recommendations for the TAF amendment criteria are included in Appendix B. Recalling the discussion of the SPECI criteria from AMOFSG/7 it can be suggested that the following proposed SPECI standards be used as the basis for the subset of criteria that should form the guidelines for TAF accuracy. The proposed new SPECI standards are included in the table in the attachment to this paper. There was some agreement that the SPECI criteria are useful reference to determine the TAF accuracy requirement. However, it was also noted that SPECI criteria sets out the thresholds above which the change in weather conditions warrants issuance of SPECI, and it lacks the information for those weather conditions below the thresholds for which, there is still a requirement for them to be verified against pre-determined accuracy requirements. For instance, the SPECI criteria for wind direction is : a change of mean surface wind direction by 60° or more from that given in the latest report given that the mean speed before and/or after the change being 10kt or more. Here we have a useful reference for accuracy requirement of wind direction for wind speed at or above 10kt. The question is: how about the wind direction for wind speed below 10kt? Arguably there is still a requirement to assess these conditions. If not, wind direction for wind speed below 10kt would not be verified which may not be fully justifiable. As well, by not verifying wind direction for wind speed below 10kt, there will be less number for TAF being verified, which would have a bearing on the ‘percentage of cases within range’ in Attachment B. It is therefore suggested to address this within the context of this exercise. It was also felt there would be value in reflecting significant changes in cloud base related to auto landing systems minima. . Discussion Point 6: It is felt that the above stated list of proposed new SPECI standards is a reasonable measure, pending user validation, of the highest priority criteria for establishing the desirable accuracy of the TAF. However it has been also noted that it may be problematic to establish quantitative guidelines for the desirable performance given the lack of TAF performance measurement information for some criteria. Discussion Point 7: Where TAF performance measurements do not exist to support a proposed minimum requirement for percentage within range, the current criteria from Attachment B should be carried forward or reduced to the lowest current percentage (70 per cent). To address this issue further it has been suggested that it would be appropriate to request from members current performance information related to the TAF. Discussion Point 8: The desirable criteria should be narrowed to areas of clear interest to international aviation that are observable while the minimum performance should be set relatively low as a preliminary guideline. Also, the TAF should be considered to be correct if any part of the forecast includes the specified condition of interest. AMOFSG/8-SN No. 9 -4- There was no comment received from the other members of the ad hoc group pertaining to this discussion point at this time. Discussion Point 9:. The TAF should be considered to be within the range if any part of the forecast (including transitory change groups – define what this includes, e.g: PROBS, TEMPOS, BECMG) is within the minimum percentage range of performance. Note: proposed changes and comments are presented in italics at below the table in the attachment to this paper. 3. ACTION BY THE AMOFSG 3.1 The AMOFSG is invited to consider the issues raised in this paper and assess if further work is required, or request the Secretary to develop appropriate revisions to Annex 3. ———————— AMOFSG/8-SN No. 9 Appendix APPENDIX PROPOSED ALIGNMENT OF OPERATIONALLY DESIRABLE ACCURACY OF FORECASTS WITH TAF AMENDMENT CRITERIA AND THE ISSUANCE OF SPECI CRITERIA (as per Annex 3) Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation Wind Wind Direction + 10º When the mean No change When the mean surface + 20º 1. Within 30 º or 60º when 80% cases 70% cases surface wind direction wind direction is wind speed is equal to or has changed by 60° forecast to change by greater than 07kts or more from that 60º or more, the mean given in the latest speed before and/or report, the mean after the Note: wind direction not speed before and/or change being 10kt or verified for wind speed at or after the change more; below 6 kt being 20km/h (10kt) or more; Wind Speed + 2 km/h (1kt) When the mean No change When the mean surface + 10 km/h (5 kt) 1. Mean value within 10kts 80% cases 70% cases up to surface wind speed wind speed is forecast 20 km/h (10kt) has changed by 20 to change by 10kt or Or km/h (10 kt) or more more; + 10% above from that given in the 2. No change 20km/h (10kt) latest report AMOFSG/8-SN No. 9 Appendix A-2 Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation Variations + 4km/h (2kt), in When the variation When the variation When the variation from from the mean terms of from the mean from the mean the mean surface wind surface wind longitudinal & surface wind speed surface wind speed (gusts) is lateral (gusts) has increased speed (gusts) has forecast to increase by components by 20 km/h (10 kt) or increased by 10kt (10 kt) or more, the more from that given or more from that mean speed before in the latest report, at the time of the and/or after the change the mean speed latest report, the being 30 km/h (15 kt) or before and/or after mean speed more; the change being 30 before and/or after When the surface wind km/h (15 kt) or more; the change being is forecast to change 15kt or more; through values of When the wind operational significance. changes through The threshold values values of operational should be established significance. The by the meteorological threshold values authority in consultation should be established with the appropriate by the meteorological ATS authority and authority in operators concerned, consultation with the taking into account appropriate ATS changes in the wind authority and which would: operators concerned, 1) require a change in taking into account runway(s) in use; and changes in the wind 2) indicate that the which would: runway tailwind and 1) require a change crosswind components in runway(s) in use; will change through and values representing the 2) indicate that the main operating limits for runway tailwind and typical aircraft operating crosswind at the aerodrome; components have changed through values representing the main operating limits for typical aircraft operating at the aerodrome. Visibility + 50m up to When the visibility is No changes When the visibility is + 200m up to 1. Occurrence or non- 80% cases 70% cases 600m improving and proposed forecast to improve and 800m occurrence of prevailing AMOFSG/8-SN No. 9 A-3 Appendix Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation + 10% between changes to or passes change to or pass visibilities less than: 600m & 1500m through one or more through one or more of + 30% between • 10 km + 20% above of the following the following values, or 800m & 10km • 5km 1500m values, or when the when the visibility is • 550 m visibility is forecast to deteriorate • 350 m deteriorating and and pass through one passes through one or more of the following or or more of the values: following values: 1) 150, 350, 600, 800, 1 2. Retain original 1) 800, 1 500 or 3 500 or 3 000 m; or 000 m; 2) 5 000 m in cases and where significant 3. Provide the proposed 2) 5 000 m, in cases numbers of flights are distances in “miles” as well as where significant operated in accordance kilometres and metres numbers of flights are with the visual flight operated in rules; Refer Note “a” below accordance with the pertaining to verification of visual flight rules; forecast visibility. Note.— In local special reports, visibility refers to the value(s) to be reported in accordance with Annex 3 184.108.40.206 & 220.127.116.11; in SPECI, visibility refers to the value(s) to be reported in accordance with 18.104.22.168. RVR + 10m up to When the runway Provide the 400m visual range is proposed + 25m between improving and distances in “feet” 400m & 800m changes to or passes as well as metres + 10% above through one or more 800m of the following values, or when the runway visual range is deteriorating and passes through one or more of the following values: 150, 350, 600 or 800 m; Weather When the onset, 1. When the When any of the 1. Occurrence or non- 70% cases Phenomena cessation or change onset, cessation or following weather occurrence of lightning within in intensity of any of change in intensity phenomena or 5 KM of any manoeuvring the following weather of any of the combinations thereof surface of the airport AMOFSG/8-SN No. 9 Appendix A-4 Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation phenomena or following weather are forecast to begin or combinations thereof phenomena or end or change in or occurs: combinations intensity: — freezing thereof occurs: — freezing precipitation 2. Retain current precipitation - freezing — moderate or heavy — moderate or heavy precipitation precipitation (including and/or precipitation - moderate or showers thereof) (including showers heavy precipitation — thunderstorm (with 3. Occurrence or non- thereof) (including showers precipitation) occurrence of any weather — thunderstorm (with thereof) — duststorm phenomena reported in a precipitation) - thunderstorm — sandstorm; SPECI and that is an element — duststorm (with precipitation); of a TAF. — sandstorm; or When any of the 2. When the onset following weather When the onset or or cessation of any phenomena or cessation of any of of the following combinations thereof the following weather weather are forecast to begin or phenomena or phenomena or end: combinations thereof combinations — ice crystals occurs: thereof occurs: — freezing fog — ice crystals - freezing fog — low drifting dust, — freezing fog - thunderstorm sand or snow — low drifting dust, (without — blowing dust, sand or sand or snow precipitation); snow — blowing dust, sand or — thunderstorm or snow 3. When the (without precipitation) — thunderstorm onset, cessation or — squall (without precipitation) change in intensity — funnel cloud (tornado — squall of any other or waterspout); — funnel cloud weather (tornado or phenomena that waterspout); are observed or measured. Precipitation Occurrence or See weather phenomena 80% cases 70% cases non-occurrence above. Cloud Cloud amount + 1 okta When the amount of NO change When the amount of a One category 1. Occurrence or non- 70% cases 70% cases a cloud layer below layer or mass of cloud below 450m occurrence of VV less than, or AMOFSG/8-SN No. 9 A-5 Appendix Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation 450 m (1 500 ft) below 450 m (1 500 ft) (1`500ft) BKN or OVC cloud based at or changes: is forecast to change: below, 450 m (1500 feet) 1) from NSC, FEW or Occurrence or 1) from SCT or less SCT to BKN or OVC; or non-occurrence of or to BKN or OVC; or 2) from BKN or OVC to BKN or NSC, FEW or SCT; OVC between 2. Within one category 2) from BKN or OVC 450m (1500ft) and (SKC/FEW/SCT/ BKN/OVC) of to SCT or less; 3000m (10 000ft) the forecast for cloud layer below 1500 ft; within same class (class 1: SKC/FEW/SCT; class 2: BKN/OVC) of the forecast for cloud layer at or above 1500 ft and below 5000 ft; Cloud height + 10m (33’) up When the height of Although no When the height of + 30m (100ft) up 1. Occurrence or non- 70% cases 70% cases to 100m (330ft) base of the lowest criteria is provided, base of the lowest layer to 300m (1000ft) occurrence of VV or base of + 10% above cloud layer of BKN or it is proposed that or mass of cloud of BKN BKN or OVC cloud less than 100m (330’) OVC extent is lifting this should be or OVC extent is + 30% between 300 m (1000 ft) and changes to or amended to also forecast to lift and 300m (1000ft) and passes through one reflect auto change to 3000m (10 000ft) or or more of the landing system or pass through one or following values, or requirements. more of the following 2. Observed cloud base of the When the height of values, or when the lowest BKN/OVC cloud layer base of the lowest height of the lowest no more than 100 ft from the cloud layer of BKN or layer or mass of cloud forecast cloud base at or OVC extent is of BKN below 1000 ft; lowering and passes or OVC extent is through one or more forecast to lower and of the following pass through one or values: more of the following 1) 30, 60, 150 or 300 values: Observed cloud base of the m (100, 200, 500 or 1) 30, 60, 150 or 300 m lowest BKN/OVC cloud layer 1000 ft); and (100, 200, 500 or 1000 no more than 30% from the ft); or forecast cloud base above 2) 450 m (1500 ft), in 1000 ft and below 5000 ft; cases where 2) 450 m (1 500 ft) in significant numbers cases where significant AMOFSG/8-SN No. 9 Appendix A-6 Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation of flights are operated numbers of flights are in accordance with operated in accordance the visual flight rules; with the visual flight rules; When the sky is When the vertical obscured and the visibility is forecast to vertical visibility is improve and change to improving and or pass through one or changes to or passes more of the following through one or more values, or when the of the following vertical visibility is values, or when the forecast to deteriorate vertical visibility is and pass through one deteriorating and or more of the following passes through one values: 30, 60, 150 or or more of the 300 m (100, 200, 500 or following values: 30, 1000ft); 60, 150 or 300 m (100, 200, 500 or 1 000 ft) Any other criteria Any other criteria based based on local on local aerodrome aerodrome operating operating minima, as minima, as agreed agreed between the between the meteorological authority meteorological and authority and the the operators. operators. Note.— Other Note.— Other criteria criteria based on based on local local aerodrome aerodrome operating operating minima are minima are to be to be considered in considered in parallel parallel with similar with similar criteria criteria for the for the issuance of inclusion of change SPECI developed in groups and for the response to Appendix 3, amendment of TAF 2.3.2 l). developed in response to Appendix 5, 1.3.1 k). AMOFSG/8-SN No. 9 A-7 Appendix Element Operationally Criteria for Proposed Criteria for TAF Current Proposed operationally Current Proposed Desirable Issuance of Criteria for Amendment operationally desirable accuracy of Min% of Min% of Accuracy for SPECI Issuance of desirable TAF cases cases Measurement SPECI accuracy of within within or TAF range range Observation Air + 1 ºC An increase in air + 1 ºC 1. + 2 ºC 70% cases 70% cases temperature C temperature of 2° or and dew- more from that given Or in the latest report, or point an alternative 2. Retain temperature threshold value as agreed between the meteorological authority, the appropriate ATS authority and the operators concerned. Pressure + 0.5 hPa Local regional value (QNH, arrangements and QFE) not specified in Annex 3 e.g: An increase of decrease of + 5hPa from that given in the latest report (Australia) Note a) For verification of forecast visibility over 800 m and to take into account the resolution of visibility reporting (100 m between 800-4999 m; 1 km between 5-10 km), the upper bound and lower bound of the forecast visibility are ‘rounded’ up and down respectively for one reporting step. For instance, a forecast visibility of 7000 m is regarded to be accurate if the observed visibility is between 4900 m and 10km (+/-30% of 7000 m are respectively 9100 m and 4900 m. Here 9100 m is rounded up by one step of 1 km to 10 km) — END —