A TAF, or Terminal Aerodrome Forecast, is a coded weather forecast for conditions expected at or near an airport. Pilots, dispatchers, air traffic planners, and aviation weather specialists use TAFs to plan departures, arrivals, alternates, fuel, and delays. A TAF is compact because it uses standard aviation weather codes for wind, visibility, weather, clouds, and timing.
Learning to read one turns a dense code strip into a practical airport weather story.
A typical TAF begins with the airport identifier and issue time, then gives a valid forecast period such as 0112/0218 for the 1st day at 1200Z through the 2nd day at 1800Z. The main forecast line describes the prevailing conditions, while change groups such as FM, TEMPO, BECMG, and PROB show when conditions are expected to change. For example, TAF KJFK 011130Z 0112/0218 18012KT 6SM -RA BKN020 FM011600 22015G25KT P6SM SCT030 means winds from 180 degrees at 12 knots, 6 statute miles visibility, light rain, broken clouds at 2,000 ft, then from 1600Z winds shift to 220 degrees at 15 knots gusting 25 with visibility greater than 6 miles and scattered clouds at 3,000 ft.
The key skill is reading the groups in order and matching each weather condition to the correct time window.
Understanding Aviation: Reading a TAF
Every time in a TAF is expressed in UTC, not local clock time. This matters most near midnight, when the UTC date may be different from the local date. Students should practise converting UTC to local time before deciding when a forecast change affects a flight.
The forecast is built around conditions that are expected to prevail, meaning they should occur for more than half of a stated period. It is not a minute by minute promise. Airport weather can change faster than a forecast update, especially near thunderstorms, fronts, coastal fog, or mountain terrain.
Wind matters because aircraft take off and land most efficiently into the wind. Runway numbers roughly match their compass direction, so a wind direction can help show whether a runway will have a headwind, tailwind, or crosswind. A gust is important because it shows short increases above the steady wind speed.
Pilots must account for gusts during takeoff and landing because aircraft control becomes less predictable. Wind direction can vary too. A forecast wind direction gives the expected general flow, not every small shift that may occur at the runway.
Cloud groups are especially important for visual flying. A ceiling is usually the lowest broken or overcast cloud layer, since those layers cover much of the sky. Scattered clouds do not normally create a ceiling, though they can still matter near hills or during an approach.
Low visibility and a low ceiling often occur together in rain, snow, fog, or haze, but they are separate limits. A pilot may be able to see far along the ground while cloud prevents climbing or approaching safely. Weather codes add useful clues.
Rain can reduce braking action. Fog can form quickly near sunrise. Thunderstorms can bring lightning, severe turbulence, hail, wind shifts, and sudden visibility loss.
The change groups need to be read as a timeline rather than as separate predictions. An FM group starts a new prevailing forecast at its listed time. Conditions after that point replace the earlier main conditions until another change appears.
A TEMPO group describes short periods within its time window, so it should not be treated as constant weather for the whole window. BECMG signals a transition, which means the exact moment may be uncertain. PROB shows that an event is possible but not certain.
When practising, write each forecast period on a simple timeline and place the wind, visibility, clouds, and weather beneath it. Then check which period covers a planned departure or arrival time. This method prevents a common mistake, which is reading an alarming temporary group as if it applies for the entire forecast.
Key Facts
- TAF = Terminal Aerodrome Forecast, a coded forecast for expected airport weather conditions.
- TAF valid time format is DDHH/DDHH, where DD is day of month and HH is hour in UTC, such as 0112/0218.
- Wind format is dddssKT or dddssGggKT, where ddd = wind direction in degrees, ss = speed in knots, and gg = gust speed.
- Visibility in U.S. TAFs is usually in statute miles, such as 6SM, 1/2SM, or P6SM for greater than 6 statute miles.
- Cloud height is given in hundreds of feet AGL, so BKN020 means broken clouds at 2,000 ft above ground level.
- Change groups include FM for a rapid change starting at a time, TEMPO for temporary conditions, BECMG for gradual change, and PROB for probability of a condition.
Vocabulary
- TAF
- A Terminal Aerodrome Forecast is a coded aviation forecast for weather expected at an airport during a stated valid period.
- Zulu time
- Zulu time is Coordinated Universal Time, written with a Z, and is the standard time reference used in aviation weather reports.
- Prevailing visibility
- Prevailing visibility is the greatest distance that can be seen throughout at least half of the horizon around the observation point.
- Ceiling
- A ceiling is the height above ground of the lowest broken, overcast, or obscured cloud layer.
- Change group
- A change group is a TAF section that tells when and how forecast weather conditions are expected to change.
Common Mistakes to Avoid
- Reading TAF times as local time is wrong because TAFs use UTC, also called Zulu time. Always convert UTC to local time only after identifying the forecast period.
- Treating every condition as lasting for the whole TAF period is wrong because FM, TEMPO, BECMG, and PROB groups limit conditions to specific time windows. Read each group in sequence and apply the newest valid group.
- Interpreting BKN020 as 20,000 ft is wrong because cloud heights in TAFs are reported in hundreds of feet above ground level. BKN020 means a broken ceiling at 2,000 ft AGL.
- Ignoring gusts in a wind group is wrong because gusts can strongly affect takeoff, landing, and crosswind planning. In 22015G25KT, the steady wind is 15 kt but gusts may reach 25 kt.
Practice Questions
- 1 Decode the valid period in this TAF header: TAF KDEN 151130Z 1512/1618. What day and UTC time does the forecast begin, and what day and UTC time does it end?
- 2 Decode this wind and cloud group: 27018G30KT 4SM -SN OVC015. What is the wind direction, sustained wind speed, gust speed, visibility, weather, cloud coverage, and cloud height in feet AGL?
- 3 A TAF shows 12008KT P6SM SCT040 TEMPO 1820/1824 2SM TSRA BKN018. Explain which conditions a pilot should expect during the TEMPO window and why those conditions matter for approach planning.