The Terminal Aerodrome Forecast, the TEMPO Group Students Skim Past, and the Destination Weather Decision That Has to Be Made Before You Leave the Ground

The Terminal Aerodrome Forecast is the single most direct answer to the question every cross-country pilot should ask before departure: what will the weather be when I arrive? Most student pilots look at the first line, see acceptable conditions, and stop reading. That’s exactly where the trouble starts.

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

A METAR tells you what conditions exist right now at a specific airport. A TAF tells you what conditions are expected over the next 24 to 30 hours at that same airport. TAFs are issued by the National Weather Service four times daily, every six hours, for airports with sufficient air traffic. You’ll find them at major and regional airports, but not at small uncontrolled strips - a gap that matters and requires a different strategy.

How to Read the TAF Header and Base Forecast

Every TAF opens with a header line containing the airport identifier, issuance time, and valid period. The valid period is written as a date-time group. A notation like 0118/0218 means the forecast runs from the 1st of the month at 1800Z through the 2nd at 1800Z. Check this every time. If you’re planning a morning departure tomorrow, confirm the TAF actually covers tomorrow morning.

After the header comes the base forecast - the prevailing conditions at the start of the valid period. It’s structured like a METAR. Wind is a five-digit group: 03015 means wind from 330° at 15 knots. Variable winds appear as VRB. Visibility is in statute miles. Sky condition uses the familiar FEW / SCT / BKN / OVC format followed by a three-digit height in hundreds of feet AGL. BKN010 is a broken ceiling at 1,000 feet. OVC005 is an overcast at 500 feet.

The base forecast is only the starting point. Everything that follows tells you how conditions will change. If you stop reading after the base forecast, you haven’t actually read the TAF.

What Do the TAF Change Groups Mean?

FM - From (Definite Persistent Change)

An FM group marks a clean, definite shift in conditions beginning at a specific time. FM1500 means: from 1500Z forward, replace all previous forecast conditions with what follows. The old conditions are gone. The new ones hold until the next change group or the end of the valid period. Students generally understand FM groups. The next type is where real trouble begins.

TEMPO - Temporary (The One Pilots Skip)

TEMPO describes conditions expected to last less than one hour at a time and occur during less than half of the specified window. That’s the official definition, and it deserves careful reading.

A TEMPO ceiling of 500 feet overcast does not mean you’ll have 500-foot ceilings throughout the window. It means that during the window, conditions may briefly drop to 500 feet and then recover. Brief is the operative word - but if you arrive during one of those brief dips, you still can’t see the runway. The forecast warned you.

TEMPO groups don’t hide. They’re labeled clearly. The challenge is that you have to actively check whether the time window overlaps with your estimated arrival - which means you need to know your ETA before you open the briefing. That’s why flight planning and weather briefing happen in that order.

BECMG - Becoming (Gradual Transition)

A BECMG group describes a gradual change to new conditions over a defined window. A notation like BECMG 0300/0500 means the shift occurs gradually between 0300Z and 0500Z. Unlike FM, the change is slow. But unlike TEMPO, the new conditions persist - they don’t revert. If a BECMG is taking you from 4,000 feet scattered down to 800 feet overcast over two hours, at some point in that window you’re sliding through everything in between.

PROB - Probability Groups

PROB30 and PROB40 indicate a 30% or 40% chance that the listed conditions will occur during the specified window. The National Weather Service doesn’t issue probability groups below 30 percent in a TAF - so if it appears, the forecasters decided it was worth including. For a VFR student pilot, a PROB40 thunderstorm in your arrival window deserves serious attention even though it isn’t a certainty.

How to Apply a TAF to a Real Cross-Country Flight

Here’s a planning scenario. You’re filing a cross-country to an airport 120 nautical miles away. Estimated flight time is 1 hour 15 minutes. Departure: 1300Z. Estimated arrival: ~1415Z.

You pull up the destination TAF and find:

• Base forecast: Winds 080 at 10 knots, visibility greater than 6 miles, few clouds at 3,000 feet. Looks good.
• FM1400: Winds 120 at 15 gusting 25, visibility 6 miles, BKN018 - a broken ceiling at 1,800 feet and a gusty crosswind. Starting right at your arrival time.
• TEMPO 1400/1530: Visibility 3 miles in rain showers, OVC008 - an overcast at 800 feet - during the same 90-minute window.

The FM group alone tells you the ceiling is dropping to 1,800 feet at your arrival. Flyable VFR, but not comfortable. The TEMPO group shows the possibility of 800-foot ceilings and 3-mile visibility during that exact window - below basic VFR minimums. That condition is sitting right on top of your arrival.

The question isn’t whether the TEMPO condition is certain. It probably won’t happen. But it might. The question to answer before you leave the ground: what is your plan if it does? Do you have a nearby alternate with clear weather? Do you have fuel to reach it? Have you checked that alternate’s TAF?

Part 91 does not require VFR pilots to file an alternate. That’s the legal floor. Your personal minimums and a mentally pre-planned alternate set your actual safety margin.

What Happens When There’s No TAF at Your Destination?

A significant number of airports student pilots fly to have no TAF - small municipal fields, grass strips, mountain airfields. For those locations, build your picture from:

• TAFs from nearby stations within 50 to 60 miles
• The Area Forecast Discussion published by the National Weather Service
• Recent METARs from surrounding airports
• PIREPs from pilots who flew the route in the last few hours

Mountain airports require extra caution. Terrain-induced weather can develop rapidly and look nothing like the valley airport 20 miles away. A lowland TAF may show VFR ceilings while a mountain pass has its own localized cloud development by mid-afternoon. When flying into any uncontrolled field without TAF coverage, pad your weather margins significantly and define your personal no-go point before engine start.

How to Present TAF Analysis on Your Private Pilot Checkride

The Airman Certification Standards for the private pilot checkride address weather products - including TAFs - as part of the preflight planning task. The examiner wants to see you apply the forecast to the actual flight, not recite abbreviations.

When handed a weather package, walk through the destination TAF out loud in this order:

1. Identify the valid period - confirm it covers your planned arrival time
2. Read the base forecast - note wind, visibility, and ceiling
3. Read every change group - every FM, TEMPO, BECMG, and PROB
4. For each change group, state the time window and whether it overlaps with your ETA
5. If it overlaps, describe the conditions it shows and what your contingency is

That’s the standard: a decision, not a recitation.

The TAF as Part of a Complete Weather Picture

A TAF is a forecast, and forecasts are sometimes wrong. That’s not a reason to treat it casually - it’s a reason to read it alongside everything else: recent METARs from the destination and nearby stations, PIREPs from pilots on the route, AIRMETs for IFR conditions or terrain obscuration, and prog charts for the broader synoptic pattern.

But of all those products, the TAF is the one pointed most directly at your destination and your arrival time. Read all of it - not just the first line.

Key Takeaways

• The TAF covers the next 24 to 30 hours at a given airport; always verify the valid period covers your planned arrival
• The base forecast is only the beginning - change groups (FM, TEMPO, BECMG, PROB) define the real risk
• A TEMPO group means brief, intermittent deterioration - not continuous - but it can still trap you if you arrive during a dip
• Know your ETA before you brief so you can check every change group’s time window against your arrival
• Part 91 doesn’t require a VFR alternate, but smart planning includes one mentally on every cross-country
• Airports without TAFs require METARs, Area Forecast Discussions, and PIREPs from surrounding stations to build a complete picture