A TAF decoder translates a terminal aerodrome forecast into plain English. A TAF is the National Weather Service forecast for the area within 5 statute miles of the center of an airport’s runway complex, usually covering 24 hours (30 hours at some major airports), and it is issued four times a day. Paste any TAF into the decoder below to see each forecast period spelled out with its flight category, then use the guide that follows to read the change groups (FM, TEMPO, PROB30 and BECMG) yourself.
TEMPO, PROB30 and BECMG groups list only the elements that change. Anything they leave out, such as the wind or the clouds, carries over from the forecast line above, so always read a change group together with the line it modifies.
The TAF header
Here is an example TAF from the FAA’s Aviation Weather Handbook (FAA-H-8083-28B):
TAF KPIR 111140Z 1112/1212 13012KT P6SM BKN100 WS020/35035KT
TEMPO 1112/1114 5SM BR
FM111500 16015G25KT P6SM SCT040 BKN250
FM120000 14012KT P6SM BKN080 OVC150 PROB30 1200/1204 3SM TSRA BKN030CB
FM120400 14008KT P6SM SCT040 OVC080 TEMPO 1204/1208 3SM TSRA OVC030CB
- TAF: a routine forecast. TAF AMD is an amended forecast, which replaces the previous TAF as soon as it is issued, so use it right away. TAF COR is a correction.
- KPIR: the ICAO identifier, here Pierre, South Dakota.
- 111140Z: issued on the 11th at 1140 UTC. Routine TAFs go out 20 to 40 minutes before the valid period begins.
- 1112/1212: valid from the 11th at 1200 UTC to the 12th at 1200 UTC. Each half is a day and an hour. An ending hour of 24 means midnight UTC, so 0600/0624 covers all of the 6th.
Forecast elements
The opening period and every FM group give the wind, visibility and clouds, plus weather and wind shear when they are expected.
- Wind: 13012KT is from 130 degrees true at 12 knots, and G marks gusts. VRB means the direction is expected to vary 30 degrees or more, either with very light winds of 1 to 6 knots (VRB05KT) or with convection (VRB15G30KT). Calm is 00000KT.
- Visibility: statute miles, with P6SM meaning more than 6 miles. When the forecast visibility is 6 miles or less, a weather or obscuration group says why.
- Weather: the same codes as a METAR, except UP. Fog that reduces visibility below 5/8 mile is FG; from 5/8 to 6 miles it is BR (mist). NSW, no significant weather, marks the end of weather forecast in an earlier group, and NWS forecasters use it only in TEMPO groups.
- Vicinity: VC means 5 to 10 statute miles from the center of the runway complex. NWS TAFs use it only as VCFG, VCSH or VCTS, and never inside a TEMPO or PROB30 group.
- Clouds: FEW, SCT, BKN and OVC with heights in hundreds of feet above ground level, VV for an obscured sky, and SKC for clear. A TAF never uses CLR. CB is the only cloud type a TAF includes, and it appears whenever thunderstorms are forecast, even VCTS. The lowest BKN, OVC or VV layer is the forecast ceiling.
WS: low-level wind shear
WS020/35035KT means non-convective wind shear from the surface up to 2,000 feet AGL, with the wind at 2,000 feet from 350 degrees true at 35 knots. The wind after the slash is the wind at the top of the shear layer, not the amount of shear. Forecasters add the group for shear within 2,000 feet of the ground that is not caused by thunderstorms, such as with a frontal passage, an inversion or a low-level jet, for example after pilot reports of airspeed gains or losses of 20 knots or more. Wind shear is always assumed in convective weather, so storms do not get a WS group. Once it appears, the WS group stays in effect until the next FM group. Our weather hazards guide covers why shear near the ground is so dangerous.
Change groups: FM, TEMPO, PROB30 and BECMG
Change groups divide the valid period whenever the forecaster expects a significant change.
| Group | What it means | What it contains |
|---|---|---|
| FM111500 | From the 11th at 1500 UTC: a lasting change expected to happen in less than an hour. Everything before it is replaced. | A complete forecast: wind, visibility and clouds, plus weather and wind shear when expected |
| TEMPO 1112/1114 | Temporary fluctuations between the two times: more than 50 percent likely, each lasting an hour or less, together covering less than half the period | Only the elements that change |
| PROB30 1200/1204 | A 30 percent chance of a thunderstorm or precipitation event, and the conditions that come with it, during the period | Only the elements that change |
| BECMG 0114/0116 | A gradual change at some point within the period, usually two hours. Not used in NWS TAFs. | Only the elements that change |
NWS rules add a few limits. PROB30 is the only probability group in NWS TAFs, although military and international TAFs may also use PROB40. The AIM notes that PROB30 does not appear in the first nine hours of an NWS TAF, and only one PROB30 group can be attached to the opening period or to each FM group. BECMG shows up in the different TAF format used at some joint civil and military airports.
Watch the dates in FM groups: FM100000 means 0000 UTC on the 10th, not 1000 UTC. The AIM’s TAF key warns about exactly this mistake.
How a TAF differs from a METAR
| METAR | TAF | |
|---|---|---|
| What it is | An observation of conditions at the station | A forecast for the area within 5 statute miles of the runway complex |
| Issued | Hourly near the top of the hour, plus SPECI reports | Four times a day, amended when it no longer fits |
| Covers | One moment | 24 hours, or 30 at some major airports |
| Best visibility shown | 10SM at automated stations | P6SM (more than 6 statute miles) |
| Clear sky | SKC or CLR | SKC only |
| Cloud types | CB and TCU | CB only |
| Temperature | Included | Not in NWS TAFs |
Use the two together: the latest METAR shows whether the forecast is on track. Our METAR decoder handles the observation side, and the guide to reading METARs and TAFs works through a complete example of each.
Which airports have a TAF?
National Weather Service forecast offices issue TAFs for about 700 U.S. airports. If your departure or destination has no TAF:
- Read the TAFs for the nearest airports that have one and compare them with current METARs along your route.
- Check the Graphical Forecasts for Aviation (GFA) on aviationweather.gov for clouds, flight category, precipitation, thunderstorms, icing, turbulence and wind.
- LAMP guidance, a statistical forecast updated hourly for more than 2,000 airports, can help with destination planning, though the Aviation Weather Handbook notes it is not the sole means.
- Get a briefing from Flight Service at 1800wxbrief.com or 1-800-WX-BRIEF.
At airports with part-time or unreliable observations, a TAF may end with AMD NOT SKED. The forecast is still valid, but amendments are not scheduled; expanded versions give the times. A NIL TAF means the forecast has been suspended. Build these checks into your cross-country planning, because TAFs are one of the weather products examiners expect you to know under the Private Pilot ACS.
What you'll need
Go deeper on forecasts and the rules behind them with these references.
Frequently asked questions
What does TEMPO mean in a TAF?
TEMPO marks temporary fluctuations that are more than 50 percent likely, last an hour or less each time, and together cover less than half of the stated period. Only the elements that change are listed; everything else carries over from the forecast above it.
What does PROB30 mean in a TAF?
A 30 percent chance of a thunderstorm or precipitation event, with the wind, visibility or clouds that come with it, during the stated period. PROB30 is the only probability group in NWS TAFs, and it is not used in the first nine hours of the forecast.
Why don’t U.S. TAFs use BECMG?
The National Weather Service does not use BECMG in its TAFs. NWS forecasters show changes with FM, TEMPO and PROB30 groups instead. BECMG, a gradual change during the stated period, appears in the different TAF format used at some joint civil and military airports.
What does P6SM mean?
Visibility greater than 6 statute miles. TAFs do not forecast visibility above that value, so P6SM is the best visibility a TAF will show.
How far from the airport does a TAF apply?
Within 5 statute miles of the center of the airport’s runway complex. Weather forecast between 5 and 10 statute miles away is coded as in the vicinity, with VC.
How often are TAFs issued?
Scheduled TAFs are issued four times a day, for periods beginning at 0000, 0600, 1200 and 1800 UTC, and an amended TAF is issued whenever the forecast no longer represents expected conditions. Some airports also receive routine amendments three hours after each scheduled issuance.