How to Read a TAF

A TAF answers a different question from a METAR.

A METAR tells you:

What weather is being observed now?

A TAF tells you:

What weather is forecast around this airport during the next several hours?

For example:

TAF KORD 081720Z 0818/0924 22012G20KT P6SM SCT040

looks complicated at first.

But it follows a predictable structure:

• TAF — forecast type
• KORD — airport
• 081720Z — issue time
• 0818/0924 — valid period
• 22012G20KT — wind
• P6SM — visibility greater than 6 statute miles
• SCT040 — scattered clouds at 4,000 feet AGL

The real challenge comes after that first line.

TAFs use time-change groups such as:

• FM
• TEMPO
• PROB30

to describe when different weather is expected and whether it is prevailing, temporary, or uncertain.

Learning those relationships is far more useful than simply memorizing abbreviations.

What Is a TAF?#

A Terminal Aerodrome Forecast is a coded forecast of meteorological conditions significant to aviation around a specific airport.

In the United States, an NWS TAF applies to the area within approximately:

5 statute miles of the center of the airport's runway complex.

That is an important limitation.

A TAF is not:

• A route forecast
• A forecast for an entire city
• A forecast for everything within the airport's approach-control airspace
• A guarantee that weather is identical at every point within the terminal area

It is a terminal forecast.

TAF Versus METAR#

This distinction should be automatic.

METAR#

Observation.

It tells you what has actually been observed at the station.

TAF#

Forecast.

It tells you what a forecaster expects during the TAF's valid period.

So if the current METAR says:

BKN008

while the TAF expected:

SCT025

the actual weather is currently worse than forecast.

That discrepancy is useful information.

It does not mean the METAR has "overridden" the TAF for the rest of the forecast period.

The forecast may:

• Recover later as expected
• Need amendment
• Continue diverging from reality

See How to Read a METAR for decoding observations.

How Long Does a TAF Cover?#

In the United States, most NWS TAFs are valid for:

24 hours

Some major airports receive:

30-hour TAFs

So:

"Every TAF is a 24-to-30-hour forecast"

is a useful U.S. summary but not a universal international rule.

Different States can use different TAF service arrangements under the international framework.

How Often Are U.S. TAFs Issued?#

Scheduled NWS TAFs are issued at least four times per day, on a roughly six-hour cycle associated with:

• 0000Z
• 0600Z
• 1200Z
• 1800Z

Some locations also receive scheduled intermediate amendments.

And a TAF can be amended whenever forecast conditions become sufficiently unrepresentative.

So: "TAFs only change every six hours"

is wrong.

Always check for the newest forecast.

A New TAF Replaces the Old One#

When an amended TAF appears:

TAF AMD

the amendment supersedes the previous TAF.

Do not keep using the older forecast until the amendment's next forecast period begins.

The amended forecast is the current forecast when it is issued.

TAF Structure#

A U.S. TAF begins with:

1. Forecast type
2. Station identifier
3. Issue time
4. Valid period
5. Initial prevailing forecast

Then change groups may divide the forecast into later periods.

A simplified example is:

TAF KORD 081720Z 0818/0924 22012G20KT P6SM SCT040

FM082300 18010KT P6SM -SHRA BKN030

TEMPO 0900/0904 3SM TSRA BR BKN015CB

FM090500 28012G20KT P6SM SCT025 BKN040 WS020/30045KT

PROB30 0912/0916 4SM -SHRA BR BKN020

We will decode this throughout the guide.

1. Forecast Type#

The report begins with:

TAF

For an amended forecast:

TAF AMD

You may also encounter corrected forecasts identified with:

COR

depending on the product and distribution context.

The important operational distinction is that an amendment changes the meteorological forecast, while a correction fixes an error in the issued product.

2. Station Identifier#

The next group identifies the airport using its four-character ICAO code.

Example:

KORD

means Chicago O'Hare International Airport.

Do not confuse:

• ICAO identifier: KORD
• IATA identifier: ORD

TAFs and METARs use ICAO-style station identifiers.

See ICAO vs IATA Airport Codes Explained.

3. Issue Time#

Example:

081720Z

means:

issued on the 8th day of the month at 17:20 UTC.

The format is:

DDHHMMZ

where:

• DD = day
• HH = hour
• MM = minute
• Z = UTC

This tells you when the forecast was produced.

It is not the same thing as the period for which the weather is forecast.

Issue Time Versus Valid Period#

This is one of the most important TAF distinctions.

Suppose:

081720Z 0818/0924

The TAF was issued:

8th at 17:20Z

but becomes valid:

8th at 18:00Z

and remains valid through:

9th at 24:00Z

Issue time answers:

When did the forecaster create this product?

Valid period answers:

During what period does this forecast apply?

4. Valid Period#

The validity group looks like:

DDHH/DDHH

Example:

0818/0924

means:

• Starts: 8th at 18Z
• Ends: 9th at 24Z

When the ending time is midnight, 24 may be used as the ending hour.

Do not misread:

0924

as:

09:24Z

It means:

the 9th day at 24:00Z.

That mistake can shift your interpretation by many hours.

5. Wind#

TAF wind groups use the familiar format:

dddffKT

Example:

22012KT

means:

• Wind from 220°
• At 12 knots

Gusts use G.

Example:

22012G20KT

means:

• Sustained 12 knots
• Gusting 20 knots

TAF Wind Is True#

U.S. TAF wind direction is referenced to true north.

That is the same reference used in the textual METAR.

But U.S. runway directions and operational tower/ATIS winds are magnetic.

So if you use a raw TAF wind to estimate future crosswind component, make sure the wind and runway headings use the same reference.

See Crosswind Explained.

Variable and Calm Wind#

A variable forecast wind may appear as:

VRB05KT

A calm forecast is:

00000KT

In current U.S. TAF practice, 00000KT is used for forecast calm conditions.

Variable direction can also occur during:

• Light winds
• Convective conditions

6. Visibility#

U.S. NWS TAF visibility is forecast in statute miles.

Example:

5SM

means:

5 statute miles

Example:

1/2SM

means:

one-half statute mile

P6SM#

A very common U.S. TAF group is:

P6SM

It means:

visibility greater than 6 statute miles

The P means:

plus / greater than

This differs from current U.S. automated METAR practice, where visibility of 10 miles or greater is normally reported as:

10SM

That is a useful METAR-versus-TAF distinction.

International TAF Visibility#

Many international TAFs use meters instead.

For example:

4000

means:

4,000 meters

and:

9999

means:

10 kilometers or greater

So an international TAF may look different from a U.S. TAF even though the underlying concepts are the same.

CAVOK#

Many ICAO States use:

CAVOK

when forecast conditions satisfy specified visibility, significant-weather, and cloud criteria.

NWS domestic U.S. TAFs do not use CAVOK.

That means a line such as:

KJFK ... 9999 ... BECMG ...

should immediately make you suspicious if it is being presented as a normal NWS-issued JFK TAF.

7. Significant Weather#

TAFs use many of the same weather codes as METARs.

Examples:

A missing significant-weather group does not mean data are broken.

It may simply mean no significant weather is forecast for that prevailing period.

NSW#

NSW

means:

No Significant Weather

But its use is jurisdiction-specific.

In current NWS domestic TAF practice, NSW is used only within a TEMPO group to show that previously forecast significant weather is temporarily expected to end.

It is not a generic "everything is good now" code.

It refers specifically to significant weather phenomena.

8. Cloud Groups#

TAFs use:

• FEW
• SCT
• BKN
• OVC
• VV

followed by height in hundreds of feet AGL.

Example:

SCT040

means:

scattered clouds at 4,000 feet AGL

BKN020

means:

broken clouds at 2,000 feet AGL

OVC008

means:

overcast at 800 feet AGL

Forecast Ceiling#

The forecast ceiling is the lowest:

• BKN
• OVC
• VV

layer.

So:

SCT010 BKN025

has a forecast ceiling of:

2,500 feet AGL

The scattered layer at 1,000 feet does not constitute a ceiling.

Vertical Visibility#

Example:

VV004

means:

vertical visibility 400 feet

This represents a total surface-based obscuration and creates an indefinite ceiling at 400 feet.

A TAF ceiling is therefore not limited to BKN and OVC.

CB#

In U.S. NWS TAFs, cumulonimbus is the only cloud type explicitly appended to a cloud group.

Example:

BKN015CB

means:

broken cumulonimbus with base at 1,500 feet AGL

This often appears with forecast thunderstorms.

TCU is not forecast as a U.S. TAF cloud-type suffix in the same way it can appear in METAR observations.

Flight Category Is Derived#

A raw TAF does not normally contain a group saying:

VFR

MVFR

IFR

or:

LIFR

Those are derived from the forecast:

• Ceiling
• Visibility

The same categories commonly used for METAR displays can therefore also be calculated for each TAF time period.

Common U.S. Flight Categories#

Use the more restrictive condition.

These flight categories are operational summaries.

They are not the same thing as:

• Regulatory VFR cloud-clearance rules
• Instrument approach minimums
• Alternate minimums

Do Not Say "VFR Means 3 Miles and a 1,000-Foot Ceiling"#

That statement mixes several different concepts.

A derived VFR weather category requires:

• Ceiling greater than 3,000 feet
• Visibility greater than 5 statute miles

Actual legal VFR weather minima depend on:

• Airspace
• Altitude
• Cloud clearance
• Other operating rules

Meanwhile, a 1,000-foot ceiling also appears in some U.S. regulatory contexts.

Those facts should not be blended into one universal "TAF VFR minimum."

Forecast Change Groups#

The most important skill in TAF reading is understanding how one forecast period relates to the next.

In a U.S. NWS TAF, the main tools are:

• FM
• TEMPO
• PROB30

International TAFs can contain additional structures such as:

• BECMG
• PROB40
• CAVOK

Do not assume every valid ICAO code is used by NWS.

FM — From#

Example:

FM082300

means:

from the 8th at 23:00Z

An FM group establishes a new set of prevailing forecast conditions.

For example:

FM082300 18010KT P6SM -SHRA BKN030

means that from approximately 23:00Z, prevailing conditions become:

• Wind 180° at 10 knots
• Visibility greater than 6 SM
• Light rain showers
• Broken cloud at 3,000 feet

FM Replaces the Previous Prevailing Forecast#

This point matters.

A U.S. FM group is self-contained.

The new FM line supplies the forecast conditions that apply after it.

The preceding prevailing forecast is superseded.

If another FM group appears later, that next FM becomes the new prevailing forecast.

FM Does Not Mean the Atmosphere Flips Like a Switch#

An FM group marks the forecaster's best timing for a significant rapid transition in prevailing weather.

FAA guidance describes FM changes as typically occurring in less than about one hour.

So:

FM082300

does not guarantee:

• Old weather at 22:59:59
• Instantly different weather at 23:00:00

Weather transitions have uncertainty.

The FM time is the forecast breakpoint around which the rapid change is expected.

FM and Fronts#

FM groups are often useful around synoptic changes such as:

• Cold-front passage
• Warm-front passage

For example, a TAF may show:

Before FM:

18012G20KT

After FM:

FM090200 29015G25KT

The TAF does not have to say:

cold front

for the forecast wind shift and accompanying weather change to reflect one.

See Air Masses & Fronts in Aviation.

TEMPO — Temporary#

Example:

TEMPO 0900/0904 3SM TSRA BR BKN015CB

means that between:

• 9th at 00Z
• 9th at 04Z

temporary conditions are expected to include:

• 3 SM visibility
• Thunderstorm with rain
• Mist
• Broken cumulonimbus at 1,500 feet

The underlying prevailing forecast remains in force outside those temporary fluctuations.

TEMPO Is Not "Maybe"#

This is one of the most important corrections.

In current U.S. NWS guidance, TEMPO conditions have a high probability of occurring.

They are expected to:

• Occur with greater than 50 percent probability
• Last one hour or less in each instance
• Occupy less than half of the total TEMPO period

So TEMPO does not mean: "The forecaster isn't sure."

It means: "These conditions are expected, but only temporarily."

Omitted Elements in TEMPO#

Suppose prevailing conditions are:

22012KT P6SM SCT030

and a TEMPO line says only:

TEMPO 0819/0822 2SM TSRA BKN015CB

The TEMPO line does not repeat the wind.

That means the previously forecast wind carries through because no temporary wind change was specified.

Only the elements that change temporarily need to appear.

That is different from FM, which is self-contained.

PROB30 — Probability#

Example:

PROB30 0912/0916 4SM -SHRA BR BKN020

means the forecaster assigns a 30 percent probability to the specified precipitation event and associated conditions during that period.

In current NWS TAFs:

• PROB30 is used
• PROB40 is not used by NWS
• PROB30 is not shown during the first nine hours of an NWS forecast

U.S. military TAFs can differ.

PROB30 Does Not Mean "30 Percent of the Time"#

A PROB30 period does not mean: "It will rain for 30 percent of these four hours."

It means approximately:

30 percent probability that the specified event/conditions will occur during the forecast period.

Probability and duration are different concepts.

TEMPO Versus PROB30#

This distinction is extremely useful.

TEMPO#

The temporary event is expected with relatively high confidence, but it will be intermittent or short-lived.

PROB30#

The event itself has lower probability.

So:

TEMPO ... TSRA

and:

PROB30 ... TSRA

communicate different forecast confidence.

BECMG — Becoming#

BECMG is an international TAF change group describing a gradual transition.

Example:

BECMG 0820/0822 24012KT

means the specified change is forecast to develop during that window rather than at one exact FM time.

However:

NWS does not use BECMG in U.S. domestic TAFs.

That deserves to be explicit in a guide intended for U.S. pilots.

You can still encounter BECMG when reading:

• European TAFs
• Canadian TAFs
• Other international products

FM Versus BECMG#

Conceptually:

FM#

A relatively rapid change to new prevailing conditions.

BECMG#

A gradual transition during a specified time window.

In an international BECMG group, only the elements forecast to change may be shown.

Other elements continue from the previous period.

Again, that differs from the self-contained U.S. FM group.

U.S. Versus International Example#

Compare these styles.

U.S.-style#

TAF KORD 081720Z 0818/0924 22012KT P6SM SCT040

FM082300 18010KT 5SM -RA BKN025

Uses:

• Statute miles
• P6SM
• FM

International-style#

TAF EDDS 081700Z 0818/0918 26008KT CAVOK

BECMG 0820/0822 22012KT

Uses:

• CAVOK
• BECMG
• ICAO-style conventions not used in domestic NWS TAFs

Both are TAFs.

They should not be taught as one identical national format.

Low-Level Wind Shear#

U.S. TAFs can forecast nonconvective wind shear.

Example:

WS020/30045KT

Break it down:

• WS — wind shear
• 020 — wind information at 2,000 feet AGL
• /
• 30045KT — wind from 300° at 45 knots at that height

This does not mean that shear exists only at one razor-thin level at exactly 2,000 feet.

The TAF group warns of nonconvective low-level wind shear in the layer from the surface through the stated low-level environment.

Why Surface Wind Matters#

Suppose the prevailing surface forecast is:

28012KT

while the TAF also contains:

WS020/30045KT

That large change between:

• Surface wind
• Wind at 2,000 feet

alerts pilots to a potentially important shear environment during:

• Takeoff
• Initial climb
• Approach
• Landing

LLWS Is Not the Same as Turbulence#

Wind shear describes a rapid change in wind.

Turbulence describes irregular atmospheric motion.

They can occur together.

They are not identical.

And the LLWS group in the TAF specifically refers to nonconvective low-level wind shear.

Thunderstorms can contain powerful wind shear without requiring this nonconvective WS group.

TAF Does Not Forecast Runway Visual Range in the Standard U.S. NWS Format#

This is another useful distinction from METAR.

A METAR may contain an observed Runway Visual Range group such as:

R28L/2600FT

Standard NWS TAFs forecast prevailing visibility, not runway-specific RVR.

So a TAF might forecast:

1/2SM FG

but the actual RVR available near approach time must come from current observations and operational reporting.

See Runway Visual Range (RVR).

TAF Does Not Decide Whether an Approach Is Legal#

A TAF can forecast:

• Ceiling
• Visibility
• Weather
• Wind

It does not know:

• Your aircraft category
• Your specific approach
• Your operator's rules
• Current RVR
• Your alternate requirements
• Your fuel situation

So: "The TAF is IFR, therefore the airport is unusable"

is wrong.

Likewise: "The TAF is VFR, therefore the flight is legal and safe"

is wrong.

Forecast weather must be compared with the requirements that actually apply to the operation.

Alternate Planning#

TAFs are extremely useful when evaluating alternates.

But:

flight category ≠ alternate minimum

A forecast airport can be categorized as:

• VFR
• MVFR
• IFR
• LIFR

while the actual alternate requirements depend on:

• Applicable regulations
• Available approaches
• Published alternate minimums
• Time window
• Type of operation

Do not substitute a weather-map color for the actual alternate-planning rules.

Forecast Weather Is Not Approach Weather#

A TAF describes expected conditions.

When the aircraft arrives, operational decisions depend on the actual weather then being reported, along with applicable procedures and regulations.

The TAF helps you plan.

The latest observations tell you what actually happened.

A Complete U.S. TAF Example#

Consider:

TAF KORD 081720Z 0818/0924 22012G20KT P6SM SCT040

FM082300 18010KT P6SM -SHRA BKN030

TEMPO 0900/0904 3SM TSRA BR BKN015CB

FM090500 28012G20KT P6SM SCT025 BKN040 WS020/30045KT

PROB30 0912/0916 4SM -SHRA BR BKN020

Now decode it chronologically.

Initial Period#

TAF KORD 081720Z 0818/0924

The TAF:

• Was issued on the 8th at 17:20Z
• Is valid from 8th at 18Z
• Through 9th at 24Z

Initial prevailing conditions:

22012G20KT P6SM SCT040

mean:

• Wind from 220° true at 12 knots
• Gusting 20
• Visibility greater than 6 statute miles
• Scattered clouds at 4,000 feet AGL
• No forecast ceiling

First FM Group#

FM082300 18010KT P6SM -SHRA BKN030

From approximately 23Z:

• Wind shifts to 180° at 10 knots
• Visibility remains greater than 6 SM
• Light rain showers become prevailing
• Broken cloud at 3,000 feet creates a 3,000-foot ceiling

Those become the new prevailing conditions.

TEMPO Group#

TEMPO 0900/0904 3SM TSRA BR BKN015CB

Between 00Z and 04Z on the 9th, temporary periods are expected with:

• 3 SM visibility
• Thunderstorm with rain
• Mist
• Broken cumulonimbus at 1,500 feet

Outside those temporary fluctuations, the prevailing FM082300 forecast still applies.

Second FM Group#

FM090500 28012G20KT P6SM SCT025 BKN040 WS020/30045KT

From approximately 05Z:

• Surface wind becomes 280° at 12 knots, gusting 20
• Visibility improves above 6 SM
• Scattered cloud at 2,500 feet
• Broken cloud at 4,000 feet
• Forecast nonconvective LLWS with wind 300° at 45 knots at 2,000 feet AGL

The prevailing ceiling is now 4,000 feet.

PROB30 Group#

PROB30 0912/0916 4SM -SHRA BR BKN020

Between 12Z and 16Z, there is a 30 percent forecast probability of:

• 4 SM visibility
• Light rain showers
• Mist
• Broken cloud at 2,000 feet

This is a lower-confidence event.

It is not expected in the same way as a TEMPO condition.

Read a TAF as a Timeline#

A common beginner mistake is decoding every group independently but never reconstructing the timeline.

A better approach is:

1. Establish the initial prevailing forecast#

What applies at the start?

2. Find every FM group#

These create new prevailing forecast periods.

3. Overlay TEMPO groups#

What temporary deterioration or improvement can occur within those periods?

4. Overlay PROB groups#

What lower-probability events are possible?

5. Check for LLWS#

Is nonconvective low-level shear forecast?

6. Find your operational time window#

Which prevailing and temporary/probability groups overlap your:

• Departure
• Arrival
• Alternate window

That is how a long coded string becomes an operational forecast.

Forecast Timing Has Uncertainty#

TAF time groups are not train schedules.

If a front is forecast with:

FM1500

the atmosphere is not promising to change at exactly:

15:00:00Z

The change may occur somewhat earlier or later.

That uncertainty becomes especially important when planning close to:

• Ceiling thresholds
• Visibility thresholds
• Thunderstorm onset
• Freezing precipitation
• Wind changes

Build margin around forecast transitions.

Comparing TAF With METAR#

Suppose the TAF expected:

P6SM SCT030

at 16Z.

But at 15:50Z the METAR says:

2SM BR OVC006

That tells you the forecast is not currently tracking well.

Useful next questions include:

• Is the poor weather improving?
• Was the TAF amended?
• What do nearby stations show?
• What does radar show?
• Is a front slower than expected?
• What does the next TAF period predict?

"TAF versus METAR" is not about picking one winner.

It is about comparing forecast versus reality.

TAF and Crosswind Planning#

TAF wind helps you anticipate:

• Runway changes
• Crosswind
• Tailwind
• Gusts

But the forecast wind is not a runway-specific component.

You still need to resolve it relative to the runway.

See Crosswind Explained.

TAF and Thunderstorms#

Forecast codes such as:

• TSRA
• VCTS
• TEMPO ... TSRA
• PROB30 ... TSRA

can indicate convective risk at the terminal.

But the TAF covers a small terminal area.

It does not describe the entire thunderstorm system along your route.

Use:

• Radar
• Convective SIGMETs
• Other convective forecasts
• Current observations
• PIREPs

as appropriate.

TAF and Icing#

A TAF can provide clues such as:

• Freezing rain
• Freezing drizzle
• Cloud
• Precipitation

but it does not describe the full vertical icing environment.

Use dedicated icing guidance and aircraft limitations.

See Aircraft Icing Explained.

TAF and Enroute Weather#

A TAF is a terminal product.

It does not replace:

• SIGMETs
• G-AIRMETs or AIRMETs where applicable
• PIREPs
• Radar
• Satellite imagery
• Turbulence forecasts
• Icing forecasts
• Broader weather analysis

A good TAF at both endpoints does not guarantee a good route between them.

Amendments Matter#

A forecast should be amended when the forecaster determines it has become unrepresentative enough to meet amendment criteria.

If your saved flight-planning screen shows:

TAF KXXX ...

but a newer:

TAF AMD KXXX ...

exists, use the amendment.

The amendment supersedes the old forecast.

Forecast Confidence Changes With Lead Time#

A TAF 20 hours into the future still has value.

But weather uncertainty generally increases with forecast lead time.

Do not turn that into an invented rule such as: "The first 12 hours are accurate and everything after 18 hours is only a trend."

There is no universal accuracy cliff at one particular forecast hour.

Instead:

• Use longer-range TAF periods for planning.
• Recheck newer forecasts as departure approaches.
• Compare the forecast against observations and the evolving synoptic picture.

Common TAF Mistakes#

Treating a TAF as an observation#

TAF is forecast.

METAR is observed.

Mixing U.S. and international syntax#

A KJFK example should not casually use 9999 and BECMG as though that were a normal NWS JFK TAF.

Forgetting the issue time#

An old TAF may have been superseded.

Misreading 0924 as 09:24Z#

In a validity group, 0924 means the 9th at 24Z.

Treating FM like an instantaneous weather switch#

It marks the expected start of a rapid transition in prevailing conditions.

Carrying old FM conditions forward#

Each FM group is self-contained and supersedes the earlier prevailing forecast.

Treating TEMPO as low probability#

TEMPO conditions are expected with relatively high confidence but occur only temporarily.

Treating PROB30 as 30 percent of the time#

It represents probability of occurrence, not duration.

Assuming BECMG is used in U.S. NWS TAFs#

It is not.

Treating omitted TEMPO elements as missing data#

Unchanged elements carry over from the prevailing forecast.

Thinking P6SM means unlimited visibility#

It means greater than 6 statute miles.

Calling every cloud layer a ceiling#

Only BKN, OVC, or VV creates a forecast ceiling.

Treating forecast flight category as legal minima#

Flight-category labels are derived planning aids.

Using TAF visibility as though it were forecast RVR#

They are different quantities.

Using the TAF as an enroute forecast#

It covers the terminal area, not the entire route.

Frequently Asked Questions#

Key Takeaways#

• A TAF is a terminal weather forecast; a METAR is an observation.
• U.S. NWS TAFs cover approximately 5 statute miles around the center of an airport's runway complex.
• Most U.S. TAFs cover 24 hours; selected major airports receive 30-hour forecasts.
• Scheduled NWS TAFs are issued at least four times daily and can be amended when necessary.
• Issue time and valid period are different.
• An amended TAF supersedes the previous forecast.
• U.S. TAF winds are forecast relative to true north.
• U.S. TAF visibility is in statute miles, with P6SM meaning greater than 6 SM.
• International TAFs may instead use meter visibility, 9999, and CAVOK.
• BKN, OVC, and VV can create a forecast ceiling; FEW and SCT do not.
• CB is the only cloud type explicitly appended in current U.S. NWS TAF cloud forecasts.
• Flight categories such as VFR, MVFR, IFR, and LIFR are derived from forecast ceiling and visibility.
• Derived flight category is not the same thing as regulatory weather minima.
• FM introduces a new prevailing forecast and supersedes the previous prevailing conditions.
• An FM time is the expected breakpoint for a rapid change, not a promise of an instantaneous atmospheric switch.
• TEMPO describes high-confidence but temporary conditions.
• In U.S. guidance, TEMPO occurrences last one hour or less each and occupy less than half of the total TEMPO period.
• PROB30 describes a 30 percent probability of occurrence, not 30 percent duration.
• NWS uses PROB30 but not PROB40, and PROB30 is not shown in the first nine hours of an NWS TAF.
• BECMG is an international change group and is not used in domestic NWS TAFs.
• Unchanged elements omitted from TEMPO or BECMG groups carry forward from the prevailing forecast.
• U.S. TAFs can forecast nonconvective low-level wind shear using a WS group.
• Standard NWS TAFs forecast prevailing visibility rather than runway-specific RVR.
• TAFs do not determine approach legality, alternate legality, or complete flight suitability by themselves.
• A TAF describes terminal weather, not the entire route.
• Comparing TAFs with current METARs is one of the best ways to judge whether the forecast is tracking.
• Forecast uncertainty increases with lead time, so newer TAFs should be checked as the flight approaches.
• TAFs should be interpreted alongside current observations, radar, PIREPs, advisories, and broader weather analysis.

Sources & References#

• FAA Aeronautical Information Manual, current edition, Chapter 7: Terminal Aerodrome Forecast format, visibility, weather, clouds, LLWS, PROB, FM, TEMPO, and BECMG distinctions.
• FAA Aviation Weather Handbook, FAA-H-8083-28B: aviation weather observations and forecasts.
• FAA Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 13: Aviation Weather Services.
• NOAA/NWS Aviation Weather Center — TAF product information and current terminal forecasts.
• NWS Instruction 10-813, Terminal Aerodrome Forecasts — current U.S. TAF preparation and coding standards.
• ICAO Annex 3, Meteorological Service for International Air Navigation, 21st Edition, August 2025 with current corrigenda — international TAF framework and coding conventions.