Terminal Aerodrome Forecast

What is TAF?

A Terminal Aerodrome Forecast is a concise, coded weather forecast issued for the airspace within 5 nautical miles of an airport's reference point. TAFs are produced by meteorological offices every 6 hours (at 00, 06, 12, and 18 UTC) and are valid for 24 or 30 hours depending on the issuing authority. Like METARs, TAFs use a standardized ICAO format readable worldwide regardless of language. The forecast includes expected wind, visibility, weather phenomena, and cloud conditions, along with anticipated changes throughout the validity period.

TAFs use specific change indicators to describe how weather will evolve. "BECMG" (becoming) indicates a gradual transition between two time points. "TEMPO" indicates temporary fluctuations lasting less than an hour at a time. "FM" (from) marks an abrupt change at a specific time. "PROB30" or "PROB40" indicate conditions with 30% or 40% probability of occurrence. These structured change groups allow dispatchers to anticipate precisely when conditions might deteriorate or improve, enabling optimal fuel planning and alternate airport selection.

Amended TAFs (TAF AMD) are issued whenever the original forecast becomes significantly unrepresentative of expected conditions. A corrected TAF (TAF COR) fixes errors in the original. The accuracy of TAFs decreases with the forecast horizon — the first 6-12 hours are generally reliable, while conditions beyond 18 hours become increasingly uncertain. For this reason, regulations require dispatchers to use the TAF for the destination and alternate airports when calculating required fuel, adding margins based on forecast uncertainty.

Why It Matters for Airspace Risk

TAFs are essential for diversion planning during airspace closures and disruptions. When a primary route becomes unavailable due to conflict, GPS interference, or volcanic ash, airlines must quickly identify viable alternates. The TAF for each potential diversion airport determines whether it will be operationally accessible for the duration of the flight. Poor weather at alternates can narrow options dramatically, particularly when airspace restrictions have already eliminated the nearest diversion points.

During large-scale airspace events, TAF availability becomes a constraint. If meteorological services in an affected region degrade — as can happen when conflict disrupts infrastructure — TAFs may stop being issued or become unreliable. Dispatchers then face a double uncertainty: restricted airspace AND unknown weather at the remaining alternate airports. For this reason, airspace risk assessment must consider not just where airspace is open, but whether the weather reporting infrastructure at available airports is functioning. The combination of airspace closure and poor TAF coverage at alternates represents a compounding risk that can ground flights preemptively.

Key Facts

• •TAFs are issued every 6 hours with 24-30 hour validity, using the same coded format as METARs.
• •Change indicators (BECMG, TEMPO, FM, PROB) describe the expected evolution of weather throughout the forecast period.
• •Airlines are required by regulation to consider TAFs for destination and alternate airports when calculating minimum fuel.
• •TAF accuracy decreases with forecast horizon — the first 12 hours are generally more reliable than conditions predicted beyond 18 hours.
• •Absence of TAF issuance for a normally forecasted airport can indicate meteorological service disruption in the region.

Related Terms