The TAF Decoded: Reading the Twelve-Hour Forecast That Lives Inside Your Standard Briefing

Reading a Terminal Aerodrome Forecast means more than checking the opening ceiling and visibility. A TAF tells a time-based story, and the most important information is often buried in the change groups that follow the base forecast. Learning to read the whole thing - methodically, from front to back - is one of the most practical skills you can build before your checkride and carry throughout your flying career.

What Is a TAF and How Is It Different from a METAR?

A TAF (Terminal Aerodrome Forecast) is a forecast of expected conditions at a specific airport, within a five statute mile radius of the field. It is produced by the National Weather Service and covers a defined time window - not a region, not a corridor, but that specific airport.

Standard TAFs are issued four times daily: at 0000, 0600, 1200, and 1800 Zulu. Most large airports and many general aviation fields receive a 24-hour TAF. Some smaller airports receive only a 12-hour forecast.

A METAR (Meteorological Aerodrome Report) is an observation - an actual measurement taken at the airport at a specific time. A TAF is a prediction. Both are essential to a complete weather picture. Neither alone tells the whole story.

How Do You Read the TAF Header?

Every TAF opens with an identification block that tells you three things: the airport identifier, when the forecast was issued, and what time period it covers.

The first thing to check is whether the TAF is current and whether it covers your planned arrival time. If it expires two hours before you plan to land, you need an amended version or need to check the next issuance schedule. If you see “AMD” in the header, that TAF has been amended - it supersedes the original for that station, and that version is the one to use.

What Does the Base Forecast Group Tell You?

After the header comes the base forecast, which describes expected conditions at the start of the valid period. It always reads in the same order: wind, visibility, weather phenomena, sky condition.

Wind is expressed as a five-digit group: direction in degrees magnetic, then speed in knots. 18012 means wind from 180 degrees (due south) at 12 knots. A G indicates gusts - 18012G25 means sustained at 12, gusting to 25. VRB means variable direction, followed by the speed.

Visibility in U.S. domestic TAFs is in statute miles. P6SM means prevailing visibility greater than 6 statute miles - essentially unlimited. Fractions indicate visibility below one mile. The legal VFR minimum is 1,000 feet ceiling and 3 statute miles visibility; 6 SM and a 1,000-foot ceiling is the common planning threshold.

Weather phenomena use standard codes: RA (rain), SN (snow), TS (thunderstorm), BR (mist), FG (fog). A minus sign (-) prefix means light; a plus sign (+) means heavy. +TSRA is heavy thunderstorm with rain - any group containing thunderstorm codes changes the character of your planning entirely.

Sky condition describes cloud layers by coverage and height above field elevation. Coverage is in eighths: Few = 1–2 eighths, Scattered = 3–4, Broken = 5–7, Overcast = 8. The number that follows is height in hundreds of feet AGL. BKN012 is a broken layer at 1,200 feet - that is your ceiling. CB attached to any coverage code means cumulonimbus: thunderstorm-producing cells.

What Are the TAF Change Groups and What Does Each One Mean?

This is where most students stop reading - and where the most critical information lives. TAFs use four change group indicators to describe how conditions evolve through the forecast period.

FM (From) marks a time at which conditions are expected to change significantly and persistently. An FM group completely replaces everything before it - new wind, new visibility, new weather, new sky condition. Think of it as a wall in your timeline: before it, one picture; after it, another. If your arrival falls after an FM group, the FM conditions are what you plan around.

BECMG (Becoming) describes a gradual transition over a specified time window. It gives a start time and an end time and says the change will be complete by the closing time - but does not commit to exactly when within that window it occurs. It is commonly used for improving conditions after a frontal passage, sea breezes in the afternoon, or radiation fog burning off in the morning.

TEMPO (Temporary) describes conditions expected to last less than 60 minutes at a time and occur for less than half of the period it covers. TEMPO is not a persistent condition - it flags brief excursions from the baseline. Common uses include thunderstorm passages and momentary visibility reductions in showers. The base forecast remains the prevailing picture; TEMPO marks the asterisks.

PROB (Probability) indicates the likelihood of a condition occurring. PROB30 is a 30 percent probability; PROB40 is 40 percent. These numbers are not reassuringly small. The NWS does not include PROB groups for minor events - they appear when the forecasted condition would be significant if it occurred. A 30% chance of embedded thunderstorms near your arrival window is worth planning around, not dismissing. PROB30 TEMPO combines both qualifiers: lower probability, brief if it occurs.

How Do You Read a TAF as a Complete Timeline?

The right technique is to treat the TAF as a timeline. Start at the beginning of the valid period. Apply the base forecast. Walk forward through time: note where FM groups shift the picture entirely, where BECMG groups trend conditions toward a new state, and where TEMPO or PROB windows open.

Write it out. Draw a timeline and mark the hours. Note what the conditions look like in each window. This forces you to synthesize the entire TAF rather than scanning the opening line. Pilots who do this consistently catch things they would otherwise have missed.

When your planned arrival falls inside or near a TEMPO window, decide in advance what you will do if those conditions are present when you arrive. Know your alternate. Verify you have fuel to hold. Set a personal decision point for when you will go missed and divert - before you depart, not while breaking out of clouds at minimums.

What Are the Less Common TAF Elements to Know?

LLWS (Low Level Wind Shear) flags the potential for rapid changes in wind speed or direction below approximately 2,000 feet AGL. Wind shear is most dangerous during takeoff and landing because it can cause a sudden airspeed loss at the worst possible moment. An LLWS advisory in a TAF is a red flag for your departure and arrival environment.

NSW (No Significant Weather) appears inside change groups to indicate that weather phenomena present in the previous group are no longer expected. It is the all-clear from the preceding condition - rain gone, fog lifted, nothing reducing visibility.

RMK (Remarks) appears less frequently in TAFs than in METARs, but when it does, read it. Remarks contain locally significant information that does not fit the standard format.

What Does the ACS Require You to Know About TAFs?

The Airman Certification Standards (ACS) requires you to demonstrate actual weather briefing proficiency - not just an understanding that weather matters, but the ability to decode a product and make a decision from it. The TAF is explicitly one of those products.

Examiners will look for you to: correctly identify the valid period, accurately decode all change groups, identify conditions at your planned arrival time, and explain how those conditions affect your go/no-go decision and alternate planning. A common checkride failure point is handling the base forecast correctly but stumbling when asked what an FM group two hours before arrival means for fuel planning and alternates. Know the entire TAF, not just the opening block.

Key Takeaways

• A TAF is a time-based forecast for a specific airport (within 5 SM); always check the issuance time and valid period first
• The base forecast covers the opening conditions; FM groups completely replace it at hard transition points
• BECMG indicates gradual change; TEMPO flags brief, non-persistent excursions; PROB marks significant-if-it-occurs conditions at 30 or 40 percent likelihood
• Any TAF group containing TS or CB requires careful attention and contingency planning
• Read the entire TAF as a written timeline - write it out if needed - rather than scanning only the first line