Decoding TAFs and turning a terminal forecast into a real go or no-go decision

Terminal Aerodrome Forecasts (TAFs) are the foundation of every smart go or no-go decision. Unlike a METAR, which tells you current conditions, a TAF projects weather 24 to 30 hours into the future at a specific airport — answering the questions that actually matter for cross-country planning: Will the weather hold when I arrive? Will it still be good for my return?

The Airman Certification Standards for the private pilot certificate require you to obtain and evaluate weather information, including terminal forecasts. Your examiner will expect you to read a TAF and apply it to your flight, not just identify one on a page.

How Do You Read the TAF Header?

Every TAF begins with the letters TAF followed by the airport’s four-letter ICAO identifier (KORD for Chicago O’Hare, KDFW for Dallas Fort Worth, KDVT for Deer Valley).

Immediately after the identifier is the issuance and valid period. This time group is critical — without it, the rest of the forecast is meaningless because you could be reading an expired product.

The format works like this:

• Issuance time: A six-digit group such as 180530Z means the forecast was issued on the 18th day of the month at 0530 Zulu.
• Valid period: A group like 1806/1906 means the forecast covers from the 18th at 0600Z through the 19th at 0600Z — a 24-hour window.

All TAF times are in Zulu (UTC). East Coast conversions: subtract 4 hours during daylight saving time, 5 hours during standard time. Central time: subtract 5 or 6. Write every converted time on your nav log or kneeboard. Mixing up Zulu and local under the stress of flight planning is one of the most common — and most dangerous — student mistakes.

What Do the Wind, Visibility, and Sky Condition Lines Mean?

The first line after the header states the prevailing conditions expected at the start of the forecast period. It reads much like a METAR: wind, visibility, weather phenomena (if any), and sky condition.

For example: 31012G20KT 6SM BKN025

• Winds from 310° at 12 knots, gusting to 20
• Visibility 6 statute miles
• Broken ceiling at 2,500 feet AGL

That’s workable VFR weather — visibility well above minimums, ceiling above the 1,000-foot VFR floor for uncontrolled airspace, and manageable (if gusty) winds. But the TAF doesn’t stop with this snapshot. It tells you how conditions will change.

What Do FM, TEMPO, and BECMG Mean in a TAF?

These three change indicators are the heart of every TAF, and misreading them is where most pilots go wrong.

FM (From)

FM followed by a time group means conditions are expected to completely change to what follows at that time. Everything after the FM line replaces the previous forecast. Think of it as crossing out the old forecast and writing a new one.

FM181500 27008KT P6SM SCT040 means: starting at 1500Z on the 18th, expect winds 270° at 8 knots, visibility above 6 miles, scattered clouds at 4,000 feet.

FM is the most important change group for flight planning. If an FM line shows deteriorating conditions near your estimated arrival time, you need a serious conversation with yourself — or your instructor — before launching.

TEMPO (Temporary)

TEMPO indicates conditions will temporarily fluctuate from the prevailing forecast during a specific window. Each fluctuation typically lasts less than one hour, and conditions bounce back and forth between the baseline and the TEMPO values.

TEMPO 1812/1816 3SM BR means between 1200Z and 1600Z, visibility may temporarily drop to 3 miles in mist before returning to the prevailing value.

Is 3 miles still VFR? Technically, yes — Class E airspace requires 3 statute miles, and Class G requires just 1. But 3 miles in mist signals a deteriorating trend. For a student or low-time pilot, a TEMPO line like this should trigger real caution.

BECMG (Becoming)

BECMG signals a gradual transition from prevailing conditions to new conditions over a specified time period. Unlike FM’s clean break, BECMG is a slow shift.

BECMG 1814/1816 OVC012 means between 1400Z and 1600Z, the sky is expected to gradually become overcast at 1,200 feet.

An overcast layer at 1,200 feet is dangerously close to IFR conditions. If you’re a VFR-only pilot, that single BECMG line just changed your entire plan.

How Do You Apply a TAF to a Real Cross-Country Flight?

Consider this scenario: you’re planning a 90-nautical-mile cross-country with a 10:00 AM local departure and an estimated flight time of 1 hour 15 minutes each way.

The TAF for your destination reads:

• 0600Z: Winds calm, visibility greater than 6 miles, few clouds at 5,000 feet. Perfect conditions.
• FM181800: Winds 170° at 15 gusting 25, visibility 4 miles in thunderstorms, broken at 2,500, overcast at 4,500.
• TEMPO 1815/1818: Visibility 2 miles in rain showers.

On the East Coast during daylight saving time, 1800Z is 2:00 PM local. Your arrival at 11:15 AM falls inside the good-weather window. But the TEMPO line shows temporary drops to 2 miles visibility starting at 1500Z — that’s 11:00 AM local.

Your window just collapsed. The major change is forecast for 2:00 PM, but reduced visibility could arrive as early as 11:00 AM — right when you’re landing. Any delay on the ground and you’re trying to depart into building thunderstorms.

This is exactly the analysis the ACS demands. The standard isn’t just “obtain weather information” — it’s evaluate it. That means converting times, identifying trends, and making a sound aeronautical decision.

How Should You Use TAFs in Your Pre-Flight Planning?

Read the entire TAF top to bottom. The first line might show perfect weather, but the FM, TEMPO, and BECMG groups later in the forecast could change everything. Weather at departure time doesn’t matter if conditions at your destination collapse during your ETA window.

Convert and write down every time. Translate each Zulu time group to your local time zone and note it on your nav log or kneeboard. This simple habit prevents the most common TAF-reading error.

Cross-reference with other products. Pull the area forecast discussion from the National Weather Service. Check METARs at surrounding airports for current conditions. Look at radar. A TAF is a forecast, and forecasts aren’t perfect — but when the TAF, radar trends, and area forecast discussion all point toward deteriorating weather, believe them.

Build personal minimums. If you’re a student or low-time private pilot, don’t plan flights that push right up against VFR minimums. A TEMPO showing 3 miles visibility during your flight window is a perfectly good reason to make it a ground school day.

Call Flight Service. You can reach a briefer at 1-800-WX-BRIEF or use the online portal. When you request a standard briefing, the briefer will walk through TAFs with you and highlight details you may have missed. They translate forecasts into practical route-specific guidance all day — use that resource.

Key Takeaways

• A TAF forecasts weather 24–30 hours ahead at a specific airport, making it essential for cross-country go or no-go decisions
• FM replaces the entire forecast from a specific time; TEMPO signals temporary fluctuations (usually under one hour); BECMG indicates a gradual shift over a time window
• Always convert Zulu times to local and write them on your nav log — this single step prevents the most common TAF mistake
• Read the full TAF, not just the first line — the most critical information often hides in the change groups later in the forecast period
• Cross-reference TAFs with METARs, radar, and area forecast discussions for a complete weather picture before committing to a flight