Understanding TAF Forecasts: The Definitive Aviation Weather Guide
Terminal Aerodrome Forecast (TAF) is the second pillar of aviation weather intelligence, complementing METAR observations with forward-looking predictions. While a METAR tells you what the weather IS right now, a TAF tells you what it WILL BE over the next 24 to 30 hours. Mastering TAF interpretation is essential for effective flight planning, fuel calculations, and alternate airport selection.
What is a TAF?
A TAF is a concise weather forecast issued for the airspace within 5 statute miles of an airport. Published four times daily (every 6 hours) at major airports and twice daily at smaller stations, TAFs use the same coded format as METARs with additional forecast-specific elements. The TAF format is standardized by ICAO Annex 3, ensuring global consistency in interpretation.
TAFs are produced by meteorologists at designated forecast offices who analyze numerical weather models, satellite imagery, radar data, surface observations, and upper air soundings. The resulting forecast represents the meteorologist expert judgment on how conditions will evolve, not simply a model output.
TAF Format Anatomy
Consider this example TAF:
TAF KJFK 151730Z 1518/1624 28012KT P6SM SCT040 BKN250 FM152200 31018G28KT P6SM BKN035 TEMPO 1522/1602 5SM -TSRA BKN025CB BECMG 1606/1608 18008KT P6SM SCT050
1. Header Information
TAF KJFK 151730Z tells us this is a TAF for JFK Airport, issued on the 15th at 17:30 UTC. The keyword TAF AMD indicates an amended forecast replacing a previous version, while TAF COR indicates a corrected forecast fixing an error.
2. Valid Period
1518/1624 defines the forecast validity from the 15th at 18:00 UTC to the 16th at 24:00 UTC (midnight). This 30-hour window is standard for major airports. Shorter TAFs cover 24 hours. Understanding the valid period prevents using expired forecast data.
3. Prevailing Conditions
The first wind, visibility, and cloud group after the valid period describes the prevailing (most likely) conditions for the initial forecast period: 28012KT P6SM SCT040 BKN250 means wind from 280 at 12 knots, visibility greater than 6 statute miles, scattered clouds at 4,000 feet, and broken clouds at 25,000 feet.
TAF Change Groups Explained
Change groups are what make TAFs powerful. They describe how and when conditions are expected to change:
FM (From) – Permanent Change
FM152200 signals a complete and permanent change in conditions beginning at 22:00 UTC on the 15th. Everything after the FM group replaces the previous conditions entirely. Use FM when planning your arrival time, as it tells you the expected conditions at a specific moment.
TEMPO (Temporary) – Fluctuations
TEMPO 1522/1602 indicates temporary fluctuations expected between 22:00 on the 15th and 02:00 on the 16th. TEMPO conditions may occur for less than half the period, interspersed with the prevailing conditions. For flight planning, you should be prepared for TEMPO conditions even though they are intermittent.
BECMG (Becoming) – Gradual Transition
BECMG 1606/1608 describes a gradual change expected to complete between 06:00 and 08:00 on the 16th. Unlike FM which is instant, BECMG gives a transition window. After the second time, the BECMG conditions become the new prevailing conditions.
PROB (Probability)
PROB30 or PROB40 indicates a 30% or 40% probability of the described conditions. PROB30 means unlikely but possible. PROB40 means a meaningful chance. You will never see PROB50 or higher because at that point the forecaster would use TEMPO or FM instead.
Weather Phenomena in TAFs
TAFs use the same weather codes as METARs but with forecast context:
- -TSRA – Light thunderstorm with rain (the minus indicates light precipitation, not a light thunderstorm)
- +SHRA – Heavy rain showers
- FZRA – Freezing rain (critical for icing assessments)
- BR – Mist (visibility 5/8 to 6 SM)
- FG – Fog (visibility below 5/8 SM)
- CB and TCU – Cumulonimbus and towering cumulus clouds (convective indicators)
Using TAFs for Flight Planning
Effective TAF usage requires a systematic approach:
- Check the valid period – Ensure the TAF covers your estimated arrival time
- Identify the applicable change group – Which FM, TEMPO, or BECMG period covers your ETA?
- Determine the worst-case scenario – Plan for TEMPO conditions if they overlap your arrival window
- Select alternates wisely – Your alternate airports need their own favorable TAFs
- Monitor for amendments – TAF AMD supersedes the original; always use the most recent version
TAF vs METAR: When to Use Each
The relationship between TAF and METAR is complementary:
- Pre-flight (hours before departure): Rely primarily on TAFs for destination and alternate planning
- Pre-departure (30-60 minutes before): Check latest METARs to confirm TAF accuracy
- En-route: Monitor METARs for real-time updates; compare against TAF expectations
- Approach: Latest METAR determines actual landing conditions and approach type
Decode TAFs Instantly on METAR&TAF
Skip the manual decoding. On METAR&TAF, every TAF is automatically decoded into plain language with visual timeline charts showing how conditions evolve. Our tools make it easy to compare forecast periods, identify weather windows, and make confident planning decisions for over 1,600 airports worldwide.
