How to Read a New Zealand TAF (Step by Step)
By Pilot Prep
Once you can decode a METAR you are halfway there. The METAR tells you what the weather is doing right now, which is useful on the ground and almost useless for planning. The TAF is the half that decides whether the flight goes.
A TAF looks harder than a METAR because it is not one set of conditions, it is several sets stacked on top of each other with rules about when each one applies. Get those rules straight and the rest is the same vocabulary you already know.
What a TAF actually is
TAF stands for Terminal Aerodrome Forecast. It is a forecast of the weather expected at an aerodrome and its immediate vicinity, conventionally taken as within about 5 nm of the aerodrome reference point.
That radius matters more than students expect. A TAF is not an area forecast. It tells you nothing about the weather in the hills ten miles down track, and a perfectly benign TAF at your destination can sit underneath a thoroughly unpleasant en route forecast.
New Zealand TAFs are issued for the main aerodromes and published alongside the METARs on IFIS.
Issue time is not validity period
This is the single most common mistake, and it is worth being deliberate about.
TAF NZWN 250458Z 2506/2606
250458Z is when the forecast was issued: the 25th at 0458 UTC. 2506/2606 is when it is valid: from the 25th at 0600 UTC until the 26th at 0600 UTC.
Those are different numbers doing different jobs, and a forecast issued an hour before it takes effect is completely normal. Validity at the main New Zealand aerodromes is commonly 24 hours, shorter elsewhere. Everything is UTC, exactly as it was in the METAR.
The base conditions
After the validity period comes one set of conditions describing what the forecaster expects for most of the period.
34025KT 9999 SCT030
Read left to right and it is the familiar order: wind from 340 true at 25 knots, visibility 10 km or more, scattered cloud at 3,000 ft above aerodrome level.
Two things are missing compared with a METAR, and their absence catches people out. There is no QNH, and there is no temperature and dew point pair. A TAF will not give you a pressure setting or let you judge the fog risk from the spread, so you still need the METAR for that.
The change groups
Everything after the base conditions modifies it. There are four indicators worth knowing, and they mean genuinely different things.
FM is an abrupt, permanent change at a stated time. FM251200 means that from the 25th at 1200 UTC, the conditions written after it replace everything before, wholesale. An FM group is a clean break.
BECMG is a permanent change too, but a gradual one. BECMG 2514/2516 means the change takes place at some point during that two hour window and then stays changed. For planning, assume the new conditions from the start of the window.
TEMPO is a temporary fluctuation, not a permanent change. Each occurrence is expected to last under an hour, and in total less than half the stated period. The conditions bounce between the prevailing forecast and the TEMPO conditions.
PROB30 or PROB40 is a probability, 30 or 40 percent, of the conditions that follow. You will never see PROB attached to FM or BECMG, because a permanent change either happens or it does not. You will often see it paired with TEMPO.
A worked example
TAF NZWN 250458Z 2506/2606 34025KT 9999 SCT030
TEMPO 2506/2512 35035G50KT 4000 SHRA BKN010
FM251200 31018KT 9999 SCT035
PROB30 2518/2523 3000 RA BKN008
Line by line:
- Issued the 25th at 0458 UTC, valid 0600 on the 25th to 0600 on the 26th.
- Most of that period: northerly at 25 knots, 10 km or better, scattered at 3,000 ft.
- Between 0600 and 1200 on the 25th, expect short bursts of 35 knots gusting 50, visibility down to 4,000 m in rain showers, broken cloud at 1,000 ft. Short bursts, not the whole six hours.
- From 1200 on the 25th the wind backs to 310 at 18 knots and it clears up. That is a permanent change, so it supersedes the base conditions.
- Between 1800 and 2300 there is a 30 percent chance of 3,000 m in rain with broken cloud at 800 ft.
Now the question that matters: can you go?
Reading a TAF for a decision, not a translation
Decoding is the easy half. The skill is turning it into a go or no-go.
Work out your window first, then read only the groups that overlap it. A TEMPO five hours after you land is not your problem.
Within your window, plan for the worst set of conditions that could legally apply. If a TEMPO group takes you below your minima, you have to be able to handle those conditions, because TEMPO means the forecaster expects them to happen, just not continuously.
Treat a PROB30 the same way but weigh it against your own margins and experience. A 30 percent chance of 800 ft broken is not a reason to cancel by itself, and it is a very good reason to have a plan and the fuel to use it.
Why understanding beats memorising
You could learn that TEMPO means temporary and move on. Plenty of students do, and they pass the decode question.
Then the exam asks what the lowest cloud base you should plan for between 0800 and 1000 is, and the answer depends on knowing that a TEMPO group applies within its window while the base conditions still apply around it. That is not a vocabulary question. It is a comprehension question, and it is the kind ASPEQ likes.
More to the point, the same understanding is what stops you launching into a valley on a day the forecaster told you, in code, that it was going to close in.