Decoding a TAF
A TAF (Terminal Aerodrome Forecast) is the forecast weather for one airport, within about 5 nm of it. It is valid 24 or 30 hours and is normally issued four times a day, about every 6 h (issue times vary by site, so the TAF states its next issue time in the remarks). Read it like a METAR, in the same order, but the fields describe what is expected, not what is observed.
TAF CYYZ 051130Z 0512/0612 24012KT P6SM FEW040 FM051700 27015G25KT 3SM -SHRA BKN020
- Issue time
051130Z: day 05, 1130Z. - Validity
0512/0612: this is day + hour, not a clock time. Valid from day 05 at 1200Z to day 06 at 1200Z. Format isDDHH/DDHH. - Wind
24012KT= from 240° TRUE at 12 kt. TAF wind is true, same as METAR. - Visibility
P6SM: the P means "plus", so greater than 6 statute miles. A plain3SMis exactly 3 SM. - Cloud
FEW040: few at 4,000 ft (height in hundreds of feet).
Change groups tell you when the forecast shifts:
| Code | Meaning |
|---|---|
FM |
From this time: a rapid change; everything after it replaces the earlier line. |
BECMG |
Becoming: a gradual change over the stated window. |
TEMPO |
Temporary fluctuations: each spell under 1 hour, totalling less than half the period. |
PROB30 / PROB40 |
a 30% / 40% probability of the stated conditions. |
Trap: reading the validity 0512/0612 as a clock time (05:12) instead of day/hour, taking TAF wind as magnetic (it is TRUE), reading P6SM as exactly 6 SM, or swapping TEMPO (brief, comes and goes) with BECMG (a lasting, gradual change).
References
- TC AIM MET 7.0