10-813 Terminal Aerodrome Forecasts - National Weather Service

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Department of Commerce ã National Oceanic & Atmospheric Administration ã National Weather Service NATIONAL WEATHER SERVICE INSTRUCTION 10-813 October 2, 2014…
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Department of Commerce • National Oceanic & Atmospheric Administration • National Weather Service NATIONAL WEATHER SERVICE INSTRUCTION 10-813 October 2, 2014 Operations and Services Aviation Weather Services, NWSPD 10-8 TERMINAL AERODROME FORECASTS NOTICE: This publication is available at: http://www.nws.noaa.gov/directives/. OPR: W/OS23 (C.Sims) Certified by: W/OS2 (M. Tew) Type of Issuance: Routine SUMMARY OF REVISIONS: Supersedes NWS Instruction 10-813, Terminal Aerodrome Forecasts, dated December 19, 2008. Changes include: Cosmetic changes in: Appendix B: Section 1.2.8 – Non-Convective LLWS Section 1.2.9.1 – Special Thunderstorm Consistency Guidance Appendix F – Removed and inserted as a hyperlink in Section 3 and Appendix C, Section 1.3.1 Signed 9/18/14 Christopher S. Strager Date Acting Director, Office of Climate, Water, and Weather Services NWSI 10-813 October 2, 2014 2 Table of Contents Page 1. General........................................................................................................................................3 2. Background..................................................................................................................................3 3. Responsibility...............................................................................................................................3 4... Terminal Aerodrome Forecast.....................................................................................................3 4.1 Coordination.......................................................................................................................3 4.2 Composing the TAF.............................................................................................................3 4.3 TAFs for Automated Systems ...........................................................................................4 4.4 Format…………................................................................................................................4 4.5 Contractions.......................................................................................................................4 4.6 TAF Corrections ...............................................................................................................4 4.7 TAF Amendments.............................................................................................................4 4.8 TAF Collectives................................................................................................................5 4.9 Issuance Times..................................................................................................................5 4.10 Time References................................................................................................................5 4.11 Update Frequency..............................................................................................................5 4.12 Length of TAF Change Groups…………………………………………………………..5 4.13 Sites with Scheduled Part-Time Observations…………………………………………...6 5. Forecaster Liability…………………………………………………………………………….6 6. Records Retention .....................................................................................................................6 7. Quality Assurance of TAFs……................................................................................................6 Appendices: A. Contractions Used In NWS TAFs........................................................................................8 B. TAF Code Elements……………………………………………………………………….10 C. Unscheduled TAFs..............................................................................................................26 D. New TAF Service, Observation Requirements and Terminating TAF Service.................32 E. TAF Code Format, Terminology, and Significant Weather Matrices...................................36 NWSI 10-813 October 2, 2014 3 1 General. This instruction describes Terminal Aerodrome Forecast (TAF) preparation by National Weather Service (NWS) Weather Forecast Offices (WFOs). TAFs, also known as Aerodrome Forecasts, are a critical element of NWS aviation weather services because they are a key product in decisions for flight planning and for aircraft movement within the National Airspace System (NAS). 2 Background. TAFs are used by a variety of aviation users, including domestic and international commercial airlines, general aviation (GA), civilian, and military operators. TAFs will be prepared, issued, and distributed on a timely basis to meet requirements of the U.S. Aviation Meteorological Authority, the Federal Aviation Administration (FAA), and the International Civil Aviation Organization (ICAO) using a code format designed by the World Meteorological Organization (WMO) for both domestic and international use. 3 Responsibility. WFO Meteorologists in Charge (MICs) are responsible for maintaining a consistent and accurate aviation forecast program for their offices. TAFs are prepared by designated NWS offices for the sites listed here. TAF sites are listed alphabetically by region, by WFO within each region, and by TAF sites, indicated by the 4-letter ICAO identifier and the location (city, town, or airport). The Office of Climate, Water, and Weather Services (OCWWS), NWS Headquarters (NWSH) will update this list as needed. 4 Aerodrome Forecast. A NWS TAF consists of the expected meteorological conditions significant to aviation at an airport for a specified time period. For the U.S., this is the area within five (5) statute miles (SM) of the center of an airport's runway complex. Forecasters will prepare and monitor TAFs using the best professional judgment to optimize timeliness and representativeness, with an awareness of the potential operational impact of each forecast element. TAFs should remain as concise as possible to describe changes in flight conditions and not exceed 6 lines (excluding a TEMPO group) except when absolutely necessary to describe relevant weather conditions. TAFs in the U.S. are prepared in the international standard for TAF code, with U.S. modifications, described in WMO Manual on Codes, WMO No. 306, Volume I.l, Part A, FM 51- X Ext. TAF, Aerodrome Forecast. U.S. modifications will be held to a minimum. 4.1 Coordination. Forecasters coordinate with the servicing Center Weather Service Unit (CWSU) in accordance with NWSI 10-803, Support to Air Traffic Control Facilities to ensure consistency between the TAF and the IDSS provided by the CWSU. Forecasters should coordinate with adjacent NWS offices to prevent inconsistencies between TAFs. TAFs should be consistent with public and other aviation products. 4.2 Composing the TAF. A complete TAF includes a forecast of surface wind (speed and direction), surface visibility, weather, obstructions to vision (if any), clouds (or vertical visibility into a surface-based obscuration), Low Level Wind Shear (LLWS), and any expected significant change(s) to one or more of these elements during the specified time period, ordinarily 24 hours. However, specified International airports require 30-hour TAFs. Forecasters should keep the following in mind when composing a TAF: a. Be aware of operationally significant weather for the airport. NWSI 10-813 October 2, 2014 4 b. Be aware of amendment criteria when formulating the forecast, but do not forecast to satisfy criteria. c. Include more detail in the first 12 hours of the TAF. The latter hours in the TAF may contain less detail and highlight significant events, as this is used for strategic planning. TAFs may also include specified significant meteorological phenomena expected to occur in the airport's vicinity (VC) during any part of the valid period as VC weather codes (VCFG, VCSH, VCTS). In the United States, vicinity is defined as an area between 5 and 10 statute miles (SM) from the center of the runway complex of an airport. The forecaster will maintain a watch of weather conditions for all pertinent TAF sites, including sites with scheduled part-time observations, automated observing sites requiring part-time augmentation, and non-augmented automated observing sites. 4.3 TAFs for Automated Systems. TAFs for Automated Surface Observing System (ASOS) and Automated Weather Observing System (AWOS) sites have limitations, and forecast TAFs for these sites should take the limitations into consideration. For example, if the forecaster expects clouds above 12,000 feet and/or zero visibility, or ice pellets, the TAF should reflect these conditions even when an automated system reports clear skies (below 12,000 feet) and/or visibility of M1/4SM (which indicates visibility of LT 1/4 SM). 4.4 Format. The format of the TAF follows ICAO standards as outlined in Appendix B. The length of a line will not exceed 69 spaces, including typed characters, spaces, returns, and the end-of-report separator. 4.5 Contractions. The only contractions used in NWS TAFs are those terms defined in this instruction and its appendices, which are derived from the WMO Codes Manual and from the ICAO document ICAO Abbreviations and Codes. In a very few cases, plain language English terms may be used. All valid contractions for TAFs are included in Appendix A. 4.6 TAF Corrections. Corrections to the TAF should be issued as soon as the forecaster becomes aware of the error. Normally a correction is issued within a half hour of the issuance of the original forecast. Corrections made later than one hour after a TAF has been issued should be sent as an amendment, with forecast conditions updated as the original mistake is corrected. 4.7 TAF Amendments. The decision to amend the TAF relies on the forecaster's assessment of existing conditions and expectations. If conditions change earlier or later than forecast but the TAF shows the expected trend and will soon recover, an amendment may not be needed. Additionally, small fluctuations in the observation should not result in a minor adjustment to the TAF (chasing the observation). However, if improving weather conditions occur sooner than forecast, then an amended TAF is necessary. TAF amendments are issued promptly when: a. Conditions meeting amendment criteria are expected or have occurred and those NWSI 10-813 October 2, 2014 5 conditions will, in the forecaster’s estimation, persist, or b. New guidance/information indicates future conditions are expected to be in a different category than originally forecast, especially in the 1-12 hour time-period. Forecasters should maintain a weather watch and amend forecasts prior to weather conditions meeting amendment criteria. Additionally, forecasters should issue TAF AMDs for significant forecast changes immediately rather than waiting for the next regularly scheduled TAF release time, even if that release time is within a half hour after the amendment time. 4.8 TAF Collectives. When a WFO transmits more than one TAF in a collective, each forecast is started on the line immediately following the previous TAF with the location identifier at the left margin. Each complete TAF is followed by an end-of-report separator (an equal sign [=]), which denotes the end of a complete TAF for each location. The end-of-report separator is followed by a return. The TAF order should be decided by the respective Regional Headquarters and remain unchanged as much as possible. Newly added airports should generally be placed at the end of the bulletin. 4.9 Issuance Times. Scheduled TAFs prepared by NWS offices are issued at least four times a day, every six (6) hours, according to the following schedule: Scheduled Issuance Valid Period 30 Hour Issuance Window 0000 UTC 0000 to 0000 UTC 0600 UTC 2320 to 2340 UTC 0300 UTC (AMD) 0300 to 0000 UTC 0600 UTC 0600 UTC 0600 to 0600 UTC 1200 UTC 0520 to 0540 UTC 0900 UTC (AMD) 0900 to 0600 UTC 1200 UTC 1200 UTC 1200 to 1200 UTC 1800 UTC 1120 to 1140 UTC 1500 UTC (AMD) 1500 to 1200 UTC 1800 UTC 1800 UTC 1800 to 1800 UTC 0000 UTC 1720 to 1740 UTC 2100 UTC (AMD) 2100 to 1800 UTC 0000 UTC 4.10 Time References. The times in TAFs are stated in Universal Time Coordinated (UTC). Time references should be as detailed and specific as supporting data and present science allow and do not need to begin at the top of an hour. The letter Z is appended to the end of the date- time group of forecast origin. The contraction UTC does not appear in either the WMO abbreviated heading or the forecast text. 4.11 Update Frequency. Each WFO may choose to routinely issue TAFs more frequently than every six hours as a method of keeping the TAF as representative as possible. Those offices providing TAFs for the FAA’s core airports provide TAFs every 3 hours. These intermediate TAFs are issued as amendments using the TAF AMD header though they will actually be issued on a scheduled basis. Offices not issuing for these airports may issue more frequent updates after coordinating the change with their Regional Headquarters. 4.12 Length of TAF Change Groups. To forecast a change in weather conditions starting at a particular time, the FM (from) contraction is used and is always a single time, to the nearest NWSI 10-813 October 2, 2014 6 minute if the expected change can be forecast to that degree of accuracy. Temporary (TEMPO) groups do not exceed four (4) hours. Probability (PROB) groups are six (6) hours or less. More information on Change Groups can be found in the appendices. 4.13 Sites With Scheduled Part-Time Observations. For TAFs with LT 24-hour observational coverage, the TAFs are valid to the end of the routine scheduled forecast period even when observations end prior to that time. The time observations are scheduled to end and/or resume is indicated by expanding the AMD NOT SKED statement. Expanded statements include: • Observation ending time (AFT Y1Y1HHmm, e.g., AFT 120200), • Scheduled observation resumption time (TIL Y1Y1HHmm, e.g., TIL 171200Z) or • Period of observation unavailability (Y1Y1HH/YeYehh, e.g., 2502/2512). TIL is used only when the beginning of the scheduled TAF valid period coincides with the time of the last observation or when observations are scheduled to resume prior to the next scheduled issuance time. When used, these remarks immediately follow the last forecast group. If a routine TAF issuance is scheduled to be made after observations have ceased, but before they resume, the remark AMD NOT SKED immediately follows the valid period group of the scheduled issuance. After sufficient data using the total observation concept has been received, the AMD NOT SKED remark is removed. Examples: TAF AMD KRWF 150202Z 1502/1600 {TAF text} AMD NOT SKED 1505/1518= TAF AMD KPSP 190230Z 1903/1924 {TAF text} AMD NOT SKED= 5 NWS Forecaster Liability. NOAA’s Office of General Counsel, Weather, Satellite and Research Section has advised that NWS forecasters are generally protected from liability when utilizing their discretion: NWS forecasters employ their discretion in issuing forecasts, including utilizing the "total observation concept" for writing and issuing TAFs. In the performance of their jobs, where NWS forecasters utilize their discretion, they are covered under the discretionary function exemption of the Federal Tort Claims Act, 28 U.S.C. §§ 2671 et seq. 6 Records Retention. Records of disseminated TAFs, including amendments, corrections, and delayed issuances, will be maintained in accordance with NWSI 10-2003, Records Retention. 7 Quality Assurance of TAFs. Performance reports to the office staff and stakeholders (airport managers/individual airlines) are encouraged to let them know how the office is supporting their mission. In aviation forecasting, the goal is to continually improve forecast service by identifying forecasting weaknesses and developing methods to strengthen those NWSI 10-813 October 2, 2014 7 weaknesses. NWS uses Stats-on-Demand as the primary program for performing verification on TAFs and WFOs verify their respective TAFs in this manner. The Aviation Focal Points (AFPs) may view individual stats for their forecasters. See NWSI 10-1601, Section 6.1.3. (NOTE: Verification is covered by two documents: NWSI 10-1601, Verification Process, and NWSM 10- 1609, Verification Procedures and Methods.) Forecast and verification results tracked using the Stats-on-Demand verification program should never be used against forecasters. NWSI 10-813 October 2, 2014 8 Appendix A Contractions Used in NWS TAFs AAx Code used in the WMO abbreviated heading to indicate an amended TAF, where x is the letter A through X (see Appendix D, Section 1.1). NOTE: AAx is not used in the forecast text. AFT After AMD Amended TAF. Used in the forecast text only. AMD is not used in the WMO abbreviated heading. BC Patches BKN Broken cloud layer [five (5) to seven (7) oktas cloud amount]. Clouds may be transparent or opaque. Lowest broken layer is implied to be the ceiling. BL Blowing BR Mist CB Cumulonimbus cloud CCCC Generic WMO format code group for a four-letter location identifier. Four-letter location identifiers for specific airports are listed in ICAO document 7910, Location Identifiers. CCx Code used in the WMO abbreviated heading to indicate a corrected forecast, where x is the letter A through X (see Appendix D, Section 1.3). CCx is not used in the forecast text. CLD Cloud DR Low drifting DS Dust Storm DU Dust DZ Drizzle FC Funnel Cloud FEW Few clouds [greater than zero (0) oktas to two (2) oktas cloud amount] FG Fog FM From the date (YY) and time (UTC) indicated by GGgg. Generic WMO format code group, indicating a significant and rapid (in less than one hour) change to a new set of prevailing conditions. GG is in whole hours, gg is in minutes. See Appendix C, Section 1.2.9.1. FU Smoke FZ Freezing G (Gust) Defined as rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls within a 10 minute time period. GR Hail (largest hailstone diameter GTE 1/4 inch) GS Small hail and/or snow pellets (largest hailstone diameter LT 1/4 inch) GT Greater than GTE Greater than or equal to HZ Haze IC Ice crystals KT Knots LT Less than LTE Less than or equal to LTD Limited MI Shallow NSW No Significant Weather. An indication that significant weather conditions, as expressed by WMO Code Table 4678, are forecast to end. See Appendix C, Section 1.2.6. OVC Overcast cloud layer [eight (8) oktas cloud amount] P6SM Visibility forecast greater than six (6) statute miles PL Ice pellets PO Well-developed dust/sand whirls PR Partial PROBC2C2 Probability of occurrence of a thunderstorm (and associated precipitation) or precipitation event, along with associated weather elements (wind, visibility, and/or sky condition) directly related to the thunderstorm or precipitation event. C2C2 refer to the probability of the event. Only PROB30 is allowed. See Appendix C, Section 1.2.9.4. PY Spray NWSI 10-813 October 2, 2014 9 RA Rain RRx Code used in the WMO abbreviated heading to indicate a delayed TAF, where “x” is the letter A through X (Appendix D, Section 1.2). RRx is not used in the TAF text. SA Sand SCT Scattered cloud layer [three (3) to four (4) oktas cloud amount] SH Showers SKED Scheduled SM Statute miles SN Snow SQ Squall SS Sandstorm TAF Aerodrome Forecast code format. The international standard for the TAF code, FM 51-X Ext. TAF, is included in WMO Manual on Codes, WMO No. 306, Volume I.1, Part A. TEMPO Temporarily. Ind
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