What a TAF covers
In the U.S., TAFs are normally issued four times a day (around 0000, 0600, 1200 and 1800 UTC), are valid for 24 or 30 hours, and describe conditions within 5 statute miles of the airport. Amendments are issued when conditions change significantly. Outside the U.S., formats follow ICAO with local differences — visibility in metres, for example.
Change groups
- FM (from) — a rapid, lasting change starting at the stated time. Everything before it is replaced.
- TEMPO — temporary fluctuations, each expected to last under an hour and together less than half the period.
- PROB30 / PROB40 — a 30 or 40 percent chance of the stated conditions.
- BECMG — a gradual change over the stated period (common in ICAO TAFs, rare in U.S. ones).
Ceiling and visibility
The ceiling is the lowest layer reported as broken (BKN) or overcast (OVC), or the vertical visibility (VV) into an obscuration. Scattered (SCT) and few (FEW) layers are not ceilings. P6SM means visibility greater than 6 statute miles. A CB suffix marks cumulonimbus clouds — thunderstorms — whatever the ceiling.
Reading it against your arrival
Work out your arrival time in UTC, then find every group that covers it: the base or FM group plus any TEMPO or PROB groups. For planning, compare the worst of those with your minimums. A TEMPO thunderstorm with gusts to 25 kt is a real possibility at that time, not a footnote.
SIGMET.si uses the same approach. It takes the worst ceiling, visibility and crosswind from all TAF groups covering the modeled arrival time and shows the raw TAF next to the finding. See the methodology.
Limits
- A TAF is a forecast for one point; conditions en route and at nearby fields can differ.
- Your arrival time is an estimate, and a delay can move you into a different group.
- Check the current METAR, PIREPs, radar and NOTAMs before you commit.
Sources
- FAA AC 00-45H, Aviation Weather Services (TAF section)
- Aeronautical Information Manual, Chapter 7, Section 1
- NOAA Aviation Weather Center data API (aviationweather.gov)
Educational summary reviewed 8 Oct 2026. Always use the current official editions and an official briefing; the Pilot in Command retains final authority under 14 CFR § 91.3. More guides in Insights.