AVIATION TERMINAL FORECASTS

Table of Contents

1....... Purpose
2....... Background
3....... Unique Terms
4....... Responsibility
5....... Requests for Preparation of New Terminal Forecasts or for Expanding Existing Part-Time Terminal Forecast Services
5.1.... Availability of Observations Required to Initiate New Terminal Forecast Service
6....... Forecast Preparation
6.1.... Minimum Observational Requirements for Routine Terminal Forecast Issuance and Continuation
6.1.1. Sites With Scheduled Part-Time Observations
6.1.2. Automated Observing Sites Requiring Part-Time Augmentation
6.1.3. Unaugmented Automated Observing Sites
6.2.0. Guidance and Coordination
6.3.0. Time References
6.4.0. Contractions
6.5.0. Dissemination and Format
6.6.0. Issuance Times
6.7.0. Sub-dividing the Terminal Forecast Valid Time Period
6.7.1. Flight Category Changes
6.7.2. Element Value Changes
7.0.0. Terminal Forecast Coding
7.1.0. Bulletin Headings
7.2.0. Forecast Text
7.2.1. Location Identifier (CCCC)
7.2.2. Date-Time of Forecast Origin Group (YYGGggZ)
7.2.3. Valid Period (Y1Y1G1G1G2G2) and Routine Issuances
7.2.4. Wind Group (dddffGfmfmKT)
7.2.5. Visibility Group (VVVV)
7.2.6. Significant Weather Group (w'w')
7.2.6.a Vicinity (VC)
7.2.7. Cloud and Obscuration Group
7.2.7.a Cloud Group (NsNsNshshshs) or SKC
7.2.7.b Obscuration Group (VVhshshs)
7.2.7.c Cloud Type
7.2.8. Non-convective Low-Level Wind Shear Group (WShwshwshws/dddffKT)
7.2.9. Forecast Change Indicators
7.2.9.a FMGGgg
7.2.9.b BECMG GGGeGe
7.2.9.c TEMPO GGGeGe
7.2.9.d PROBC2C2 GGGeGe
8.0.0. Unscheduled Forecasts
8.1.0. Amended Forecasts
8.2.0. Delayed Forecasts
8.3.0. Corrected Forecasts
8.3.1. Correcting Amended or Delayed Forecasts
9.0.0. Severe Weather Watch (WW)
10.0.. Records Retention
11.0.. Verification of Terminal Forecasts

Appendices:

A - Airports for Which NWS-Prepared Terminal Forecasts are Required: Sorted by Responsible NWS Office

B - Airports for Which NWS-Prepared Terminal Forecasts are Required: Sorted by State and
Airport Name

C - Terminal Forecast Philosophy

1. Use of the Terminal Forecast
2. Composing the Terminal Forecast
3. Amendment Criteria
4. Amendment Philosophy
5. Probability Term Use Restriction
6. Length of BECMG, TEMPO, and PROB Time Periods
7. Liability Concerns

D - Terminal Forecast Issuance Guidelines

E - Contractions Used In Terminal Forecasts

F - Generic International TAF Code Format

G - International Terminology and Forecast Groups Not Used in NWS Terminal Forecasts

1. International TAF Terms Not Used in NWS-Prepared Terminal Forecasts.

2. Terms or Groups Used Differently in NWS-Prepared Terminal Forecasts than in International Terminal Forecasts

2.1 Cloud Heights (hshshs)
2.2 BECMG GGGeGe

H - U.S. Terminal Forecast Minimum Amendment Criteria

I - Significant Weather: WMO Code Table 4678

J - Significant Weather Phenomena Matrix for NWS-Prepared Terminal Forecasts

K - Acronyms

1. Purpose. This chapter describes the preparation, by designated National Weather Service (NWS) offices, of aviation terminal forecasts, which may be referred to as terminal or aerodrome forecasts. Terminal forecasts are scheduled to be issued every six hours and are valid for a 24-hour period. Amendments are issued as needed. These forecasts are used by a wide variety of aviation customers, including domestic and international commercial airlines, general aviation, civilian, and military customers.

Terminal forecasts serve the pre-flight and in-flight meteorological service requirements of aviation operations by providing a forecast of weather conditions at an airport. It is the policy of the United States that, to the extent practicable, terminal forecasts shall be prepared, issued, and distributed on a timely basis to meet requirements of the United States Aviation Authority, the Federal Aviation Administration (FAA), and the International Civil Aviation Organization (ICAO) in a code format designed by the World Meteorological Organization (WMO) for both domestic and international use.

2. Background. Terminal forecasts in the U.S. shall be prepared in the TAF code, FM 51-X Ext. TAF, Aerodrome Forecast, with U.S. modifications. 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. The U.S. modifications, or national coding practices in WMO terminology, shall be held to a minimum. The procedures and policies described in this chapter reflect the national coding practices of the United States and the NWS.

The U.S., as a WMO Member State, is obligated to advise the WMO of national coding practices adopted by the U.S. The WMO Manual on Codes, WMO No. 306, Volume I.1, Part A, is the basic document to which U.S. national coding practices apply.

Similarly, the U.S., as a Contracting State of the ICAO, has agreed to provide service for international civil aviation in accordance with ICAO standards and recommended practices with a proviso for the notification to ICAO, on a compulsory basis, of any differences between U.S. national regulations and practices and ICAO standards and, on a voluntary basis, of any differences between U.S. national regulations and practices and ICAO recommended practices.

ICAO Annex 3, "Meteorological Service for International Air Navigation", is the operating document that prescribes the relevant ICAO standards and recommended practices.

In accordance with WMO TAF code instructions, terminal forecasts shall at least contain information about surface wind, visibility, weather (when appropriate), and clouds or vertical visibility. In addition, NWS-prepared terminal forecasts shall include, on an as-required basis, forecasts of non-convective low-level wind shear.

NOTE: In this chapter, the contraction "TAF" will only be used to refer to the code FM 51-X Ext. TAF. The forecast products themselves are referred to as "terminal forecasts".

3. Unique Terms. The terms defined below are used in this Weather Service Operations Manual (WSOM) chapter to specify the degree of obligation with reference to stated procedures or practices.

"SHALL" -- means that a procedure or practice is mandatory;

"SHOULD" -- means that a procedure or practice is recommended;

"MAY" or "NEED NOT" -- means that a procedure or practice is optional; and

"WILL" -- means futurity, not a requirement to be applied to a procedure or practice.

 

4. Responsibility. Aviation terminal forecasts shall be prepared by designated NWS offices for the airports listed in Appendix A (list of terminal forecasts sorted by NWS-issuing office) and Appendix B (list of terminal forecasts sorted by state). These Appendices include the 4-letter location identifier of the airport, the city or town in which the airport is located, and name of the airport for which terminal forecasts are prepared. Appendices A and B also designate terminal forecasts required only for domestic operations and those required for both international and domestic operations.

NWS offices assuming additional (new) terminal forecast responsibility shall be designated by Regional Operations Manual Letters (ROMLs).

Terminal forecasts are a critical element of NWS aviation weather services. Forecasters shall monitor these products and their preparation using the best professional judgement to optimize terminal forecast timeliness and representativeness.

Regional Aviation Meteorologists (RAMs), or their equivalent in regions without a RAM staff position; Weather Service Evaluations Officers (WSEOs); Warning Coordination Meteorologists (WCMs) and/or any meteorologist designated by the Meteorologist-in-Charge (MIC) shall regularly review terminal forecasts for compliance with these instructions.

NWS offices preparing terminal forecasts should maintain an awareness of how well terminal forecasts are verifying and should ensure that necessary amendments and corrections are issued promptly.

5. Requests for Preparation of New Terminal Forecasts or for Expanding Existing Part-Time Terminal Forecast Services. Requests by the FAA to establish new terminal forecast service or to expand the hours of existing part-time terminal forecast service, stating the validated requirement, should be sent to the appropriate RAM (or equivalent) for evaluation. The NWS region shall recommend the FAA request be approved or disapproved based on availability of data (refer to Section 5.1) and NWS resources to support the newly requested terminal forecast(s). The regional recommendation shall be forwarded to the Chief, Integrated Hydrometeorological Services Core of the NWS' Office of Meteorology.

At locations where part-time manual observations are replaced with 24-hour automated observations, part-time terminal forecast service is not automatically increased to 24 hours. Any increased terminal forecast service must be requested by the FAA and evaluated by the NWS based on availability of data and NWS resources.

Requests by local aviation interests, airlines, or any source other than the FAA, to establish new terminal forecast service or to expand the hours of existing part-time terminal forecast service shall be forwarded by the receiving NWS office to the appropriate NWS regional headquarters. The NWS regional office shall forward the request to the appropriate FAA regional office.

Upon NWS Headquarters approval, the NWS Region responsible for the requested terminal forecast shall respond to the appropriate FAA regional office to notify them if the request was approved or disapproved. If the request for a new terminal forecast(s) is approved, the responsible NWS Region shall also initiate and submit a Data Review Group (DRG) Request for Change to add the terminal forecast to the appropriate NWS communication systems. Once the DRG has approved the request, the DRG shall arrange for the product(s) to be added to the appropriate NWS communication systems, the FAA's Weather Message Switching Center Replacement (or its replacement), the Family of Services, and other appropriate federal data communications systems. The requesting FAA region should be advised that the new terminal forecast service will not begin until it has confirmed arrangements that the FAA communications system can accommodate the product.

5.1 Availability of Observations Required to Initiate New Terminal Forecast Service.
As part of the procedures to establish a terminal forecast for an airport where the NWS is not currently preparing one, airport operators shall, at a minimum, ensure regular hourly and special observations of the following weather elements:

wind velocity (speed and direction)
visibility
weather and obscurations
sky condition
temperature
dew point temperature
altimeter setting

Absence of any one of the elements listed above from either the observation itself or supplementary and/or complementary data sources on a regular basis shall preclude the NWS agreement to initiate new terminal forecast service for that location.

Commissioned automated surface observation sites providing Automated Surface Observing System (ASOS) or Automated Weather Observing System (AWOS)-3-type observations (see FAA document 7900.5A, Surface Weather Observing - METAR, Chapters 4 and 5) and meeting either of the following conditions, shall be eligible for terminal forecast service:

a. Attended or unattended automated surface observation sites with systems that meet or exceed the performance specifications of the ASOS, and which the MIC of the office that would issue the associated terminal forecast determines have sufficient supplementary, complementary and/or augmented observation data coverage and availability.

b. Automated surface observation sites, with systems that meet or exceed FAA-specified AWOS-3 performance requirements, and that the MIC of the office that would issue the associated terminal forecast determines have sufficient supplementary and complementary observation data coverage and availability and/or that have appropriate manual augmentation by certified observers. Appropriate manual augmentation is defined as that which adds, as a minimum, those elements provided by commissioned ASOS systems that are not otherwise available from an AWOS-3.

Augmentation shall be provided in accordance with the agency agreements with augmenters (refer to FAA document 7900.5A, Surface Weather Observing - METAR, Chapters 4 and 5). If theelements listed above are reliably provided, it is NWS policy that the total available data, including those from remote sensor systems such as satellite, radar, profilers, etc., shall be sufficient to support initiation of new terminal forecast service for that airport, and to support preparation and maintenance of a terminal forecast issued under the procedures, including amendment procedures, detailed in this chapter.