6.2 TAF Decoding

6.2 TAF Decoding

Quick Answer: A TAF is a Terminal Aerodrome Forecast—what meteorologists expect at/near an aerodrome over a validity period. Change groups matter: FM (from a time, rapid lasting change), TEMPO (temporary fluctuations), BECMG (becoming—gradual change), PROB (probability). Decode wind, visibility, weather, and cloud the same way as METARs, but treat every line as forecast. Advanced pilots pick mission windows from TAFs and confirm with live METARs/SPECI before arming motors.

If the METAR is the weather photograph, the TAF is the weather movie script. Clients book drone flights hours or days ahead; your professional edge is reading whether the afternoon TEMPO thunderstorm line will erase the mapping window—or whether a BECMG improvement after 18Z is worth waiting for.

TAF role and issuance / validity

Header example pattern:

TAF CYVR 151130Z 1512/1618 27010KT ...

• Issued 15th at 1130Z
• Valid from 15th 12Z through 16th 18Z (illustrative structure—always parse the printed numbers)

Exam skill: do not confuse issuance time with validity start. A TAF issued at 1130Z may become valid at 12Z.

Anatomy of the forecast body

After the header, the TAF lists one or more forecast periods with the same meteorological language as METARs:

• Wind: dddssKT or dddssGggKT
• Visibility: SM
• Weather: -SHRA, TSRA, FZDZ, etc.
• Cloud: FEW/SCT/BKN/OVC + hundreds of feet; SKC/NSC when applicable in forecast coding
• Optional wind shear or other groups in some products (know they exist; focus exam effort on wind/vis/wx/cloud + change groups)

The base forecast applies from validity start until the first change group alters it.

Change groups: FM, TEMPO, BECMG, PROB

These four control when and how confidently conditions change. They are high-yield on the Advanced exam and in real dispatch.

FM (From)

FM151800 means from 15th 1800 UTC, expect a rapid, lasting change to the new conditions. The previous prevailing forecast is superseded from that time.

RPAS use: If FM brings TSRA or G30KT at your planned launch, move the mission earlier—or cancel—rather than hoping the FM “might be late.”

TEMPO (Temporary)

TEMPO 1520/1524 2SM -SHRA BKN008 means temporary fluctuations between 20Z and 24Z on the 15th to those conditions. TEMPO conditions are expected to last less than half of the TEMPO period in aggregate teaching models (they come and go), while the prevailing forecast still frames the period.

RPAS use: TEMPO low vis or low BKN can still kill a VLOS window even if “most of the afternoon is fine.” Build buffers; do not schedule a one-shot battery-critical survey only inside a TEMPO risk band without contingency.

BECMG (Becoming)

BECMG 1614/1616 31008KT P6SM SKC means conditions gradually become the new group between 14Z and 16Z on the 16th. Change is expected during that window, not as a single knife-edge instant.

RPAS use: Good for planning a late-day improvement (fog burn-off, wind easing). Bad for assuming the new conditions exist at the start of the BECMG window.

PROB (Probability)

PROB30 1518/1522 1/2SM FG means 30% probability of those conditions in that time window. PROB40 is also common. PROB indicates uncertainty, not a guarantee of occurrence—or of non-occurrence.

RPAS use: Treat PROB TS, PROB freezing precip, or PROB very low vis as mission risk. Clients hear “only 30%”; professionals hear “non-trivial chance of no-go.”

Worked example

TAF (illustrative Canadian-style decode practice):

TAF CYWG 200530Z 2006/2112 18012KT 3SM BR BKN008
     TEMPO 2006/2012 1/2SM FG VV002
     FM201200 27015G25KT P6SM SCT030
     BECMG 2018/2020 30008KT
     PROB30 2100/2106 4SM -SHRA BKN020

Narrative decode:

1. Header: Winnipeg (CYWG), issued 20th 0530Z, valid 20th 06Z to 21st 12Z.
2. Base from 06Z: Wind 180°/12 kt, 3 SM, mist, broken 800 ft — low ceiling and reduced vis; poor VLOS survey weather.
3. TEMPO 06–12Z: Temporarily as low as 1/2 SM fog, vertical visibility 200 ft — fog bank risk; do not plan launch in this window.
4. FM 12Z: Wind shifts westerly 15G25, visibility better than 6 SM, scattered 3,000 ft — major improvement, but gusts to 25 kt may exceed multirotor limits.
5. BECMG 18–20Z: Wind eases to 300°/08 kt — better for stable hover photography after the becoming window completes.
6. PROB30 overnight: 30% chance light showers and broken 2,000 ft — monitor; not a certainty.

Advanced pilot mission window: Earliest realistic precision VLOS work might be after 12Z if gusts are acceptable for the aircraft, preferably after ~20Z when wind eases—subject to live METAR confirmation. Morning fog TEMPO is a no-go.

How Advanced pilots use TAFs for mission windows

1. List hard constraints from manuals: max wind/gust, min temp, precip limits, IP rating honesty.
2. Highlight red lines in the TAF: TS, CB, FZ*, FG with low SM, G gusts above limit, low BKN/OVC if you need sky texture or altitude margin under cloud.
3. Mark green windows between FM/BECMG improvements and before the next TEMPO threat.
4. Add buffers for setup, battery cycles, and client delays—weather windows shrink when people are late.
5. At the site, re-check latest METAR/SPECI, glance at sky and wind, and be willing to scrub. The TAF never overrules CAR 901.34(1) VLOS and manual compliance at the moment of flight.
6. Controlled airspace / aerodrome proximity: manned traffic may be IFR or low on approach when ceilings fall—your authorization does not make weather safer.

METAR (observation) vs TAF (forecast)

Exam line to memorize: A METAR tells you what was measured; a TAF tells you what is expected. Planning without a TAF is flying blind into the afternoon; launching without a METAR is ignoring the present.

Common TAF exam traps

• Reading TEMPO 1416 as “14 to 16 days” or “wind 14 gust 16” — it is time UTC (day-hour pairs in full groups).
• Treating PROB30 as “won’t happen.”
• Assuming BECMG conditions apply from the first minute of the window.
• Forgetting FM replaces the previous prevailing forecast from that time.
• Confusing TAF validity with METAR observation time.
• Ignoring AMD — always use the latest amendment.

Integration with Chapter 5 meteorology

TAF language encodes the physics you already studied:

• Closing T/Td and FG/BR lines → saturation and fog (radiation or advection).
• TS/CB and sharp TEMPO gusts → unstable air and thunderstorm outflows.
• Persistent BKN/OVC low + DZ → stable moist layers.
• Strong gradient winds in FM groups → mechanical turbulence at low level for multirotors.

Bottom line: Decode TAF headers and change groups as carefully as METAR body groups. Build mission windows from FM/BECMG improvements, respect TEMPO and PROB risks, and confirm with current observations. Observation plans the next five minutes; forecast plans the next five hours—Advanced pilots use both.