A Terminal Aerodrome Forecast (TAF) is the standard ICAO format for aerodrome weather forecasts. Issued by certified meteorologists every 3 or 6 hours, TAFs cover a 9, 24, or 30-hour window within 5 nm of the airport and encode expected wind, visibility, weather, and cloud layers using the same tokens as METAR but arranged with change groups.

What is the difference between BECMG and TEMPO?

BECMG (Becoming) indicates a gradual, permanent change that occurs within a specified 2-hour window. TEMPO indicates conditions that temporarily fluctuate but return to the base forecast; each TEMPO episode lasts less than 60 minutes and accounts for less than half of the period.

What does FM mean in a TAF?

FM (From) marks a rapid, complete replacement of all previous conditions starting at the given time (DDHHmm format). Everything after FM overrides the base forecast for the remainder of the TAF unless another FM or group follows.

What is PROB30 or PROB40?

PROB followed by 30 or 40 indicates a 30% or 40% probability of the described conditions occurring during the following time window. PROB30 and PROB40 are the only valid probability values in ICAO TAFs; anything else is not standard.

What does NSW mean in a TAF?

NSW (No Significant Weather) explicitly cancels any previously forecast weather phenomenon in a BECMG or TEMPO group, indicating conditions return to nil significant weather after the change.

How do I read cloud layers like BKN025CB?

The sky condition group has coverage (FEW = 1–2 oktas, SCT = 3–4, BKN = 5–7, OVC = 8), height in hundreds of feet AGL, and an optional suffix CB (cumulonimbus — thunderstorm) or TCU (towering cumulus). BKN025CB means broken cumulonimbus at 2,500 ft AGL — a significant thunderstorm hazard.

TAF Decoder

Paste a raw ICAO TAF string and get a plain-English breakdown of validity, wind, visibility, weather phenomena, cloud layers, and every change group.

Paste TAF String

Paste the full raw TAF string including station ID and validity period. Multi-line or single-line input is accepted.

Try a sample:

Summary

Paste a raw ICAO TAF string and get a plain-English breakdown of validity, wind, visibility, weather phenomena, cloud layers, and every change group.

How it works

Paste or type a raw TAF string into the input field — include everything from the ICAO station ID onward.
Click "Decode TAF" or press Enter to parse the forecast.
The base forecast section appears first, showing validity period, wind, visibility, weather, and cloud layers.
Each change group (BECMG, TEMPO, FM, PROB) appears as a separate card below with its own time window and amended conditions.
Weather codes are translated to plain English — precipitation types, intensity, sky coverage, and more.
Use the sample buttons to explore real-world TAF examples before entering your own.

Use cases

Quickly understand a TAF during preflight planning without memorizing ICAO codes.
Identify IFR periods and change groups when filing an IFR flight plan.
Teach student pilots how Terminal Aerodrome Forecasts are structured.
Cross-check decoded values against ForeFlight or official aviation weather services.
Review historical TAFs for route analysis or incident investigation.
Study for the FAA Instrument Rating written exam.

Frequently Asked Questions

Last updated: 2026-09-20 · Reviewed by Nham Vu

TAF Decoder

Use the TAF Decoder

Summary

How it works

Use cases

Frequently Asked Questions