TAF – Terminal Aerodrome Forecast

Overview

A Terminal Aerodrome Forecast (TAF) is a highly-structured, concise weather forecast designed specifically for the vicinity of an airport. TAFs are vital for aviation safety and efficient flight operations, providing a snapshot of expected weather conditions within a five statute mile (SM) radius from the runway. Crafted in a coded ICAO standard format, TAFs allow rapid, unambiguous interpretation by pilots, dispatchers, and air traffic controllers worldwide.

TAFs are not observations but forecasts, usually covering 24 or 30-hour periods, depending on an airport’s size and traffic. They are updated at least every six hours and can be amended at any time if weather changes are expected.

Purpose and Importance

TAFs are essential for:

• Preflight Planning: Pilots use TAFs to determine whether weather at the departure, destination, and alternate airports will allow for safe takeoff, flight, and landing.
• Operational Decision-Making: Dispatchers and air traffic controllers rely on TAFs for airport availability, delay management, and runway assignment.
• Regulatory Compliance: Many aviation authorities require TAFs for flight legality and alternate airport selection, especially under instrument flight rules (IFR).

By focusing on the immediate airport area, TAFs provide more relevant and actionable information than broader regional forecasts.

Types of TAF Reports

TAFs are issued in several forms:

• Routine TAF: Scheduled forecast, typically four times daily.
• Amended TAF (TAF AMD): Issued when there are significant forecast changes.
• Corrected TAF (TAF COR): Corrects formatting or transmission errors.
• Delayed TAF (TAF RTD): Indicates a delay in issuance.

TAF Structure and Components

A TAF consists of several ordered elements as per ICAO standards:

1. Type of Report: “TAF”, “TAF AMD”, “TAF COR”, or “TAF RTD”.
2. ICAO Station Identifier: Four-letter airport code (e.g., KATL, EGLL).
3. Date and Time of Origin: Issuance time in UTC (“DDHHMMZ”).
4. Valid Period: The forecast’s start and end time (“DDHH/DDHH”).
5. Forecast Meteorological Conditions: Includes wind, visibility, weather phenomena, sky condition, and, when relevant, wind shear, icing, or turbulence.
6. Change Groups: Indicate transitions or probability of weather changes (FM, TEMPO, PROB, BECMG).

Example TAF Explained

TAF KJFK 091130Z 0912/1018 18012KT P6SM BKN070
     FM091500 20015G25KT P6SM VCSH BKN060
     TEMPO 0918/0922 3SM -SHRA OVC030

• TAF: Routine forecast
• KJFK: John F. Kennedy International Airport, NY
• 091130Z: Issued on the 9th at 1130Z
• 0912/1018: Valid from the 9th at 1200Z to the 10th at 1800Z
• 18012KT: Wind from 180° at 12 knots
• P6SM: Visibility greater than 6 statute miles
• BKN070: Broken clouds at 7,000 feet AGL

Change groups:

• FM091500: From 1500Z, wind 200° at 15 knots, gusting to 25 knots, showers in vicinity, broken clouds at 6,000 feet.
• TEMPO 0918/0922: Temporarily between 1800Z and 2200Z, visibility 3SM, light showers, overcast at 3,000 feet.

Decoding TAFs: Step-by-Step Example

TAF KPIT 091730Z 0918/1024 15005KT 5SM HZ FEW020 WS010/31022KT
     FM091930 30015G25KT 3SM SHRA OVC015
     TEMPO 0920/0922 1/2SM +TSRA OVC008CB
     FM100100 27008KT 5SM SHRA BKN020 OVC040
     PROB30 1004/1007 1SM -RA BR
     FM101015 18005KT 6SM -SHRA OVC020
     BECMG 1013/1015 P6SM NSW SKC

• KPIT: Pittsburgh International Airport
• 091730Z: Issued on the 9th at 1730Z
• 0918/1024: Valid from the 9th at 1800Z to the 10th at 2400Z
• 15005KT: Wind from 150° at 5 knots
• 5SM: Visibility 5 statute miles
• HZ: Haze
• FEW020: Few clouds at 2,000 feet AGL
• WS010/31022KT: Wind shear at 1,000 feet, wind from 310° at 22 knots

Change groups:

• FM091930: From 1930Z, wind 300° at 15 knots, gusting to 25 knots, 3SM visibility, showers, overcast at 1,500 feet.
• TEMPO 0920/0922: Temporarily 2000Z-2200Z, 1/2SM visibility, heavy thunderstorms/rain, overcast at 800 feet with cumulonimbus (CB).
• FM100100: From 0100Z on the 10th, wind 270° at 8 knots, 5SM, showers, broken at 2,000 feet, overcast at 4,000 feet.
• PROB30 1004/1007: 30% probability of 1SM visibility in light rain and mist between 0400Z-0700Z on the 10th.
• FM101015: From 1015Z, wind 180° at 5 knots, 6SM, light showers, overcast at 2,000 feet.
• BECMG 1013/1015: Becoming P6SM, no significant weather, sky clear between 1300Z-1500Z on the 10th.

TAF Weather Codes and Terminology

Weather Qualifiers

Weather Phenomena

Sky Condition Codes

• Vertical Visibility: “VVxxx” (e.g., “VV008” = 800 feet AGL) is used when the sky is totally obscured.

TAF Change Groups: FM, TEMPO, PROB, BECMG

• FM (From): Rapid, significant, and lasting change; all forecast elements are restated.
  • Format: “FMDDHHMM” (e.g., “FM301100”)
• TEMPO (Temporary): Brief, temporary changes, less than 1 hour at a time and not exceeding half the period.
  • Format: “TEMPO DDHH/DDHH”
• PROB (Probability): Probability (30% or 40%) of a specified condition during a period.
  • Format: “PROB30 DDHH/DDHH”
• BECMG (Becoming): Gradual change over the period. Only changing elements are listed.
  • Format: “BECMG DDHH/DDHH”

Practical Applications and Limitations

Applications

• Pilot Briefings: Primary source for airport weather during preflight checks.
• Dispatch Planning: Used to assess airport availability and alternate requirements.
• ATC Operations: Essential for runway sequencing and flow management.
• Weather Risk Mitigation: Helps reduce diversions, delays, and accidents.

Limitations

• Local Coverage: TAFs only cover the airport and immediate area (5 SM radius).
• Coded Format: Requires training to interpret accurately.
• Forecast Inherent Uncertainty: Subject to amendment if conditions change unexpectedly.
• Rare Weather: Some rare phenomena (e.g., microbursts) may not be forecast in TAFs.

TAF vs. METAR

Global Standardization

TAFs are governed by ICAO Annex 3 and the WMO, ensuring interoperability worldwide. This means a TAF for London Heathrow is read the same way by pilots from any country, supporting global aviation safety and efficiency.

Frequently Asked Questions

Q: How do I read a TAF if I’m new to aviation?
A: Start by learning the codes for wind, visibility, weather, clouds, and change groups. Practice with real TAFs and use decoding charts. Many online tools are available for practice.

Q: How often do TAFs change?
A: At least every 6 hours, but an amended TAF can be issued any time weather changes significantly.

Q: Why are TAFs important for alternates?
A: Regulations often require an alternate airport if destination TAFs predict below-minimum weather during arrival. TAFs help determine legal alternates.

Q: Where can I find TAFs?
A: TAFs are available from national meteorological services, flight planning websites, aviation weather apps, and ATC briefings.

Summary

A TAF is a cornerstone tool in aviation meteorology, providing essential, standardized weather forecasts for airport areas. It supports safe, efficient, and legally compliant flight operations, and is indispensable for pilots, dispatchers, and controllers worldwide. Understanding how to interpret TAFs is a fundamental skill for every aviation professional.