TAF (Terminal Aerodrome Forecast)

A Terminal Aerodrome Forecast (TAF) is the authoritative meteorological forecast product for conditions at a specific aerodrome and its immediate vicinity (typically within 5 statute miles of the aerodrome reference point). TAFs are standardized globally by ICAO Annex 3 (Meteorological Service for International Air Navigation) and the associated WMO Technical Regulations No. 49 Volume II Part 1, with additional FAA-specific guidance published in FAA Order 7900.5 (Surface Weather Observing) and AC 00-45 (Aviation Weather Services). The product exists to give pilots and dispatchers a forecast of surface and near-surface conditions as distinct from the current observed conditions provided by a METAR.

In the FAA system, TAFs are issued four times per day at 0000, 0600, 1200, and 1800 UTC and are valid for 24 hours (with AMD — amended — TAFs issued as needed when conditions deviate materially from the forecast). ICAO-standard TAFs, used in most EASA and other international states, have a 30-hour validity at major aerodromes and may be issued for 9-hour or 24-hour periods at smaller stations. The issuing authority in the United States is the NWS Aviation Weather Center (AWC) in Kansas City. TAFs are issued only for aerodromes with approved observation programs — roughly 900 locations in the US versus hundreds of thousands of public-use airports that receive no TAF coverage.

The TAF format mirrors METAR in many fields but expresses forecast intent using change groups. After the TAF header (station, issue time, validity period in DDHH/DDHH), the body consists of a base forecast period followed by one or more change indicators: FM (From — an abrupt change at a specified time, replacing all preceding elements), BECMG (Becoming — a gradual change expected to be complete within a 2-hour window), TEMPO (Temporary — fluctuating conditions expected to last less than one hour at a time and to occur for less than half of the change period), and PROB30 or PROB40 (a 30% or 40% probability of the associated conditions occurring). ICAO prohibits PROB40 from being used within the first 6 hours of a TAF's validity; PROB30 requires that the condition be significant enough to affect operations. In the US, PROB30 is used only for TEMPO qualification — a further departure from ICAO practice.

For IFR flight planning, the TAF is the regulatory backbone of alternate airport selection. Under 14 CFR §91.169, an alternate airport is required when the destination's forecast weather at the estimated time of arrival (ETA) ±1 hour indicates a ceiling below 2,000 ft AGL or visibility below 3 statute miles (the "1-2-3 rule"). Under §121.625 and §135.221, Part 121 and Part 135 operators have more restrictive dispatch alternate requirements that also rely on TAF analysis. The alternate airport's own TAF must then meet the alternate weather minimums: for an airport with a precision instrument approach, ceiling ≥600 ft and visibility ≥2 SM at the ETA; for a non-precision approach, ceiling ≥800 ft and visibility ≥2 SM.

TAF accuracy degrades significantly beyond 12–15 hours, and experienced dispatchers treat the outer portions of a 24-hour TAF as planning guidance rather than a precise forecast. The FM, BECMG, and TEMPO group boundaries are particularly critical for instrument instructors teaching cross-country flight planning, as misreading a TEMPO group that brackets the planned arrival window can lead to a filed flight plan that technically complies with the §91.169 alternate requirement while operationally carrying material weather risk.

For flight schools operating instrument rating training, the TAF is the central document in every cross-country dispatch brief. Instrument students must not only decode the forecast correctly but also evaluate whether change group timing conflicts with their planned arrival window, whether a PROB30/40 TEMPO for low IFR conditions near ETA requires an alternate, and whether the alternate's TAF is within published alternate minimums. This analysis chain is tested in detail on the FAA Instrument Rating Knowledge Test and evaluated on the IFR practical test — making TAF fluency a core curriculum objective, not merely background knowledge.

At the school operations level, the morning TAF check governs the day's booking viability for IFR training flights. A TAF forecasting TEMPO LIFR conditions between 1400 and 1800Z may force the cancellation or modification of all afternoon cross-country IFR dual lessons and repositioning flights scheduled for that window, with downstream effects on instructor availability, student progression timelines, and aircraft utilization.

Aviatize's smart planning and booking module allows schools to configure weather-based booking validation rules that reference TAF forecasts alongside METAR observations. When a TAF for the departure or destination airport contains change groups that bracket a scheduled booking with forecast conditions below the school's defined training minima, the system can flag those bookings for dispatcher review at scheduling time — eliminating the common scenario where a lesson is confirmed on the schedule two days in advance and then canceled the morning of because conditions were always going to be marginal.

For instrument rating programs, Aviatize can structure lesson templates that require a TAF review step as part of the preflight approval workflow, ensuring that cross-country IFR lessons are only confirmed when a compliant alternate analysis has been completed. This creates a documented paper trail that satisfies Part 141 course audit requirements and helps chief instructors verify that students are receiving the TAF interpretation practice mandated by the instrument rating curriculum before attempting their practical test.