Reading the TAF and the twenty-four hour forecast that tells you whether the weather will be there when you arrive

The Terminal Aerodrome Forecast (TAF) is a coded weather product that predicts conditions at a specific airport for the next 24 to 30 hours. Unlike a METAR, which tells you what the weather is doing right now, the TAF tells you what it’s going to do—making it essential for any flight longer than about 30 minutes. If you can read a TAF fluently, you can see hours into the future at your destination.

Why Do I Need the TAF If I Already Have the METAR?

The METAR is a snapshot. It tells you current conditions at a single moment. But weather changes, and if your flight takes two hours, the conditions at your destination when you arrive might look nothing like they did when you checked before departure.

The TAF bridges that gap. A human forecaster at the Aviation Weather Center analyzes models, surface observations, and incoming systems, then writes a coded prediction for a specific airport over a specific time window. If your estimated time of arrival falls inside that window, the TAF is talking directly to you.

How Do I Read the TAF Header Line?

A TAF header looks like this:

TAF KMCI 141730Z 1418/1524

Breaking it apart:

• TAF — identifies this as a Terminal Aerodrome Forecast
• KMCI — the station identifier (Kansas City International)
• 141730Z — issuance time: the 14th day of the month at 1730 Zulu
• 1418/1524 — valid period: from the 14th at 1800Z through the 15th at 2400Z (a 30-hour window)

If your ETA falls inside that valid period, this forecast applies to your flight. If it doesn’t, you need a newer TAF.

How Do I Decode the Initial Forecast Group?

The first line after the header describes expected conditions at the start of the valid period:

25012G20KT P6SM SCT040 BKN080

• Winds from 250° at 12 knots, gusting 20
• Visibility greater than 6 statute miles
• Scattered clouds at 4,000 feet
• Broken layer at 8,000 feet

This looks almost identical to METAR coding because it uses the same format. The critical difference: this isn’t an observation. It’s a prediction.

What Does FM (From) Mean in a TAF?

FM signals a complete change in conditions at a specific time. Think of it as a hard line—everything before is the old weather, everything after is new.

FM150200 36015G25KT 4SM BR OVC015

Starting at 0200Z on the 15th: wind shifts to 360° at 15 gusting 25, visibility drops to 4 miles in mist, ceiling drops to overcast at 1,500 feet. That’s a cold front passage written in code—wind shift, visibility drop, ceiling crash.

If your arrival falls after an FM time, that FM group is your weather, not the nicer conditions at the top of the TAF.

What Does TEMPO Mean in a TAF?

TEMPO indicates temporary fluctuations. The conditions described will happen, but not continuously. Each occurrence generally lasts less than one hour, and they cover less than half the specified time period.

TEMPO 1420/1500 2SM TSRA BKN025

Between 2000Z on the 14th and 0000Z on the 15th, visibility may temporarily drop to 2 miles in thunderstorms with a broken ceiling at 2,500 feet—but it will come and go.

Can you legally depart VFR if a TEMPO group shows below-VFR conditions during your arrival window? Technically yes, because the prevailing forecast may still be VFR. But if you’re a student pilot looking at a TEMPO group with thunderstorms during your arrival window, reschedule. There will be another day to fly.

What Does BECMG (Becoming) Mean?

BECMG describes a gradual transition over a time window. Unlike FM’s hard line, BECMG is a slope—conditions slide from one state to another.

BECMG 1504/1506 3SM OVC010

Conditions gradually deteriorate between 0400Z and 0600Z on the 15th, ending at 3 miles visibility with an overcast ceiling at 1,000 feet.

How Do PROB Groups Work?

PROB30 or PROB40 followed by a time period and conditions indicates the probability of those conditions occurring.

Important rules about PROB groups:

• The NWS never issues PROB groups below 30% or above 50%
• If probability exceeds 50%, conditions go into the main forecast
• You will never see PROB20 or PROB10—if probability is that low, it’s not mentioned

How Do I Use a TAF for Go/No-Go Decisions?

Here’s a practical scenario. You’re planning a VFR cross-country to KMCI. Departure at 1600Z, two hours enroute, arrival at approximately 1800Z.

The TAF shows:

1. Initial forecast (valid from 1200Z): Winds south at 8, visibility 6+, SCT050/BKN100—beautiful
2. TEMPO 1700/2100: 2SM TSRA BKN020—temporary thunderstorm drops
3. FM2200: 32020G30KT 3SM BR OVC012—frontal passage, solid IFR

Your 1800Z arrival lands in the middle of that TEMPO window. The prevailing conditions might be VFR, but you could arrive during a temporary thunderstorm drop. Any delay—extra time on run-up, an additional pattern at departure—pushes you deeper into that window.

The Airman Certification Standards for private pilot explicitly require you to obtain, read, and analyze weather forecasts and make a competent go/no-go decision. The examiner wants to see this kind of thinking, not just decoding ability.

Five Tips That Trip Up Student Pilots

1. TAFs always use Zulu time. Confusing 1800Z with 1800 local when reading a change group could put you in weather you didn’t expect. Write your local offset on your kneeboard until conversions are automatic.

2. Not every airport has a TAF. Only airports with capable weather stations get them. If your destination doesn’t have one, find the nearest airport that does, and account for differences caused by terrain or water.

3. Read time groups, not line order. Don’t assume conditions get progressively worse from top to bottom. Find the group valid during your arrival window and focus there. Weather at 2200Z doesn’t matter if you’re on the ground by 1900Z.

4. Compare the TAF to the current METAR. If the TAF says scattered at 5,000 but the METAR already shows broken at 3,000, conditions are diverging from the forecast. Check for an amended TAF. If actual conditions are already worse than forecast, assume the trend continues.

5. Check TAFs along your route, not just at your destination. If three airports along your route all show deterioration at the same time, something is moving through—a front, an outflow boundary. The enroute weather matters too.

The TAF Is Not a Guarantee

The TAF is a professional meteorologist’s best estimate. Sometimes it’s dead on. Sometimes the front moves faster than expected and everything shifts two hours early. That’s why you check weather during preflight planning, again before starting the engine, and stay in the loop enroute.

But no other product gives you a precise, coded forecast for a specific airport over a specific time period with change groups telling you exactly when and how conditions will shift. That’s the difference between a pilot who checks the weather and a pilot who understands it.

References: FAA Advisory Circular on Aviation Weather Services; National Weather Service TAF format guidelines.

Key Takeaways

• The TAF forecasts conditions 24–30 hours ahead at a specific airport—check it anytime your flight exceeds 30 minutes
• FM = hard change at a specific time; TEMPO = temporary fluctuations; BECMG = gradual transition over a window
• Always match your estimated arrival time to the correct TAF change group—don’t just read the top line
• Compare the TAF against the current METAR before departure to catch forecast divergence early
• Check TAFs along your entire route, not just at your destination