3.5 Reading TAF Reports
Key Takeaways
- TAFs forecast airport weather for 24-30 hours and are issued 4 times daily (0000Z, 0600Z, 1200Z, 1800Z).
- FM = abrupt change replacing all prior conditions; TEMPO = temporary fluctuations; BECMG = gradual change.
- PROB30 and PROB40 are the only probability groups used, meaning 30% or 40% chance.
- P6SM means visibility greater than 6 statute miles (P = plus/greater than).
- To answer a TAF time question, walk the change groups chronologically to the target time.
Decoding the TAF
A Terminal Aerodrome Forecast (TAF) predicts conditions within about 5 statute miles of an airport for 24 to 30 hours. TAFs are issued four times daily at 0000Z, 0600Z, 1200Z, and 1800Z. Most fields use METAR coding, plus change groups that show how the forecast evolves — the heart of TAF exam questions.
TAF KORD 121720Z 1218/1318 27012KT P6SM SCT030 BKN050
FM130200 33008KT P6SM FEW040 SCT250
TEMPO 1304/1308 2SM BR OVC010
BECMG 1310/1312 18015G25KT 3SM -RA OVC020
PROB40 1302/1306 1SM +TSRA BKN015CB
Header and Valid Period
| Element | Example | Meaning |
|---|---|---|
| Type | TAF | Terminal Aerodrome Forecast |
| Station | KORD | ICAO id |
| Issued | 121720Z | 12th, 1720 UTC |
| Valid period | 1218/1318 | From 12th 1800Z to 13th 1800Z (24 hr) |
Valid-period and change-group times read as DDHH (day-day / hour-hour). 1218/1318 = the 12th at 1800Z through the 13th at 1800Z.
Initial Forecast Line
The line after the header is the prevailing forecast at the start of the period:
- 27012KT = from 270 deg at 12 kt
- P6SM = visibility greater than 6 SM (P = plus/greater than)
- SCT030 BKN050 = scattered 3,000 ft, broken 5,000 ft; ceiling 5,000 ft
Change Groups
| Group | Behavior | Replaces prior line? |
|---|---|---|
| FM (From) | Abrupt, rapid change at a stated time | Yes — new baseline |
| BECMG (Becoming) | Gradual change over a 2-hr window | Yes, by the window's end |
| TEMPO (Temporary) | Brief fluctuations, under 1 hr each | No — base resumes between |
| PROB30 / PROB40 | 30% or 40% probability of the stated conditions | No — a possibility |
FM130200 33008KT P6SM FEW040 SCT250 — starting 13th 0200Z, the whole forecast switches to wind 330 deg/8 kt, >6 SM, few 4,000 ft.
TEMPO 1304/1308 2SM BR OVC010 — between 13th 0400Z and 0800Z, conditions may briefly drop to 2 SM mist with a 1,000 ft overcast, each occurrence under an hour, covering under half the window.
BECMG 1310/1312 18015G25KT 3SM -RA OVC020 — between 13th 1000Z and 1200Z conditions gradually become wind 180 deg/15 kt gust 25, 3 SM, light rain, 2,000 ft overcast, complete by 1200Z.
PROB40 1302/1306 1SM +TSRA BKN015CB — 40% chance between 0200Z and 0600Z of 1 SM, heavy thunderstorm rain, broken cumulonimbus at 1,500 ft. CB appended to a layer flags cumulonimbus.
TAF vs. METAR
| Feature | METAR | TAF |
|---|---|---|
| Nature | Current observation | Forecast |
| Coverage | Snapshot now | 24-30 hours |
| Issued | Hourly / special | 4 times daily |
| Change groups | No | FM, BECMG, TEMPO, PROB |
| Question it answers | What IS the weather? | What WILL it be? |
Solving a "At This Time" Question
Work the groups in order to the target time. Example: What is the forecast at 130500Z?
- The FM130200 line is in effect (active since 0200Z): wind 330/8, >6 SM, few 4,000.
- TEMPO 1304/1308 overlaps 0500Z, so a temporary drop to 2 SM mist, 1,000 ft overcast is possible.
- PROB40 1302/1306 also overlaps, adding a 40% chance of a thunderstorm.
For Part 107 planning, treat any TEMPO or PROB40 drop below 3 SM or below a 500 ft clearance as a trigger to have a quick landing plan, and a PROB40 +TSRA in your window is a reason to postpone.
A Second Walkthrough
Using the sample TAF, find conditions at 130700Z (13th, 0700Z):
- The FM130200 baseline is active: wind 330/8, >6 SM, few 4,000, scattered 25,000 — no ceiling, well above Part 107 needs.
- TEMPO 1304/1308 still overlaps 0700Z, so brief drops to 2 SM mist with a 1,000 ft overcast are possible — that overcast at 1,000 ft would temporarily threaten cloud clearance if you climbed, and the 2 SM visibility falls below the 3 SM minimum during those windows.
- PROB40 and BECMG do not cover 0700Z, so they are ignored at this time.
The planning conclusion: conditions are generally legal, but the TEMPO group means you should be ready to land within minutes if the mist materializes. That is exactly the judgment the exam wants — pick the conditions in force at the stated time, then decide.
Day/Time and Group-Order Cautions
TAF times are DDHH in UTC. 1218/1318 spans the 12th 1800Z to the 13th 1800Z. Within change groups, the first four digits after FM are also DDHH(MM). A frequent error is reading 1318 as 1:18 p.m. or as the 13th at 1800 local — it is the 13th at 1800 Zulu. Always convert mentally to UTC and to the correct calendar day, because a TAF routinely crosses midnight Z.
Common TAF Traps
- Treating TEMPO/PROB as the new baseline. Only FM and BECMG carry forward; TEMPO and PROB are overlays on the active line.
- Forgetting PROB is only 30 or 40. A 50% or higher chance is written into the prevailing forecast or a BECMG/FM group, never as PROB50.
- Misreading P6SM. P means greater than, so P6SM is better than 6 SM, not exactly 6.
- CB on a layer. BKN015CB flags cumulonimbus at 1,500 ft — a thunderstorm signal, not just a cloud height.
Exam tip: Remember FM and BECMG carry forward (replace the line), while TEMPO and PROB do not — the base conditions still apply between them.
In a TAF, the change group "FM130200" means:
Which statement about the TEMPO change group is correct?
In a TAF, visibility shown as "P6SM" means: