How to Read a TAF: FM, TEMPO, PROB30 and the Rest, Decoded

A TAF (Terminal Aerodrome Forecast) is a forecaster's picture of the weather expected at one airport. It is written with the same weather codes as a METAR (Aviation Weather Handbook, p. 27-6), so the parts that are new are the time groups and the change groups: FM, TEMPO and PROB30. Read a TAF in three passes. First the opening line, to see where and when it applies. Then the opening forecast. Then each change group in turn, building a timeline of the day.

What a TAF covers

• Where: the area within 5 statute miles of the center of the airport's runway complex (Aviation Weather Handbook, p. 27-6). If your site is farther out, treat the forecast as a guide only.
• Which airports: National Weather Service forecast offices issue TAFs for nearly 700 U.S. airports. Most run for 24 hours; some major airports get a 30-hour forecast (Aviation Weather Handbook, p. 27-6).
• What's missing: temperature. The NWS TAF doesn't forecast it (Aviation Weather Handbook, p. 27-6).
• When: scheduled TAFs are issued four times a day, at 0000, 0600, 1200 and 1800 UTC, and a routine TAF goes out 20 to 40 minutes before its valid period starts (Aviation Weather Handbook, p. 27-8). Each new TAF cancels the previous one for that airport (Aviation Weather Handbook, p. 27-20).

For a drone pilot, a TAF is a planning tool. Part 107 requires you to assess the local weather before every flight (14 CFR 107.49(a)(1)). FAA guidance says local aviation weather reports with current and forecast conditions are one means of determining visibility and cloud clearance (AC 107-2A, para. 5.12.3), and it points remote pilots to the National Weather Service's free Aviation Weather Center site for TAFs (AC 107-2A, para. B.3.1).

The opening line

Take the header TAF KOMA 121120Z 1212/1312 from the example later in this post:

• TAF is the report type. An amended forecast says TAF AMD and a corrected one TAF COR (Aviation Weather Handbook, p. 27-7).
• KOMA is the airport's four-letter ICAO identifier (Aviation Weather Handbook, p. 27-8).
• 121120Z is when the forecast was issued: the 12th at 1120 UTC (Aviation Weather Handbook, p. 27-8).
• 1212/1312 is the valid period, from 1200 UTC on the 12th to 1200 UTC on the 13th. In each half, the first two digits are the day and the last two the hour. A period that ends at midnight UTC uses 24, so a 24-hour TAF starting at midnight UTC on the 15th is valid 1500/1524 (Aviation Weather Handbook, p. 27-8).

Forecasters amend a TAF when, in their judgment, it no longer represents the conditions they expect (Aviation Weather Handbook, p. 27-7). An amended TAF replaces the earlier one the moment it is issued, so use it straight away rather than waiting for its valid period to begin (Aviation Weather Handbook, p. 27-8).

The opening forecast

Right after the valid period comes the forecast for the start of the period. The same groups open every FM period too (Aviation Weather Handbook, p. 27-9).

• Wind: three digits for the mean direction, in degrees true and rounded to the nearest 10°; two for the mean speed in knots (three at 100 knots or more); then G and the peak gust if gusts are expected. VRB in place of a direction means it is expected to vary by 30° or more. That happens in two situations: with convective activity, or when the wind is very light, from 1 to 6 knots. 00000KT is calm (Aviation Weather Handbook, p. 27-9).
• Visibility: statute miles followed by SM, with P6SM meaning more than 6 miles (Aviation Weather Handbook, p. 27-10).
• Weather: the METAR codes. Whenever a TAF forecasts visibility of 6 miles or less, it includes at least one weather group (Aviation Weather Handbook, p. 27-10). Fog that brings visibility below 5/8 mile is coded FG; fog that restricts it to between 5/8 and 6 miles is coded BR, mist (Aviation Weather Handbook, p. 27-12). In the main periods, VC can add fog, showers or thunderstorms 5 to 10 statute miles from the center of the runway complex, coded VCFG, VCSH or VCTS (Aviation Weather Handbook, pp. 27-12 to 27-13).
• Clouds: a cover amount (FEW, SCT, BKN, OVC) with the base height above ground in hundreds of feet; or VV, the vertical visibility into a surface-based obscuration; or SKC when no cloud is expected. A TAF never uses CLR (Aviation Weather Handbook, pp. 27-13 to 27-14). Read the forecast ceiling as the lowest height at which the cover adds up to 5/8 of the sky or more. The only cloud type a TAF names is CB, cumulonimbus (Aviation Weather Handbook, p. 27-14).
• Wind shear: a WS group at the end of a period forecasts non-convective low-level wind shear from the surface up to 2,000 feet AGL (Aviation Weather Handbook, p. 27-14). In WS018/25038KT, the digits after WS are the top of the shear layer, 1,800 feet AGL, and the group after the slash is the wind at that height, from 250° at 38 knots. That group is a wind, not a measure of how strong the shear is (Aviation Weather Handbook, p. 27-15). A drone flying within the 400-foot limit (14 CFR 107.51(b)) would be inside that layer.

The change groups

FM, TEMPO and PROB are the change indicators in NWS TAFs (Aviation Weather Handbook, p. 27-15). Times in all three are UTC.

• FM (from) plus six digits for the day, hour and minutes: conditions are expected to change significantly, over less than an hour, at that time. The FM group is a fresh, complete forecast. It replaces everything before it and lasts until the next FM group or the end of the TAF (Aviation Weather Handbook, p. 27-15). Every element is repeated in it, changed or not, except that the weather group is left out when no significant weather is expected (Aviation Weather Handbook, p. 27-16). FM121700 means from 1700 UTC on the 12th.
• TEMPO plus a start and an end (day and hour): temporary fluctuations that have a better than even chance of happening, last an hour or less each time, and add up to less than half of the stated period. A TEMPO group lists only the elements that will change; anything it leaves out keeps its value from the main forecast (Aviation Weather Handbook, p. 27-16).
• PROB30 plus a start and an end: a 30 percent chance of a thunderstorm or precipitation event, with the wind, visibility and sky that would go with it. It is the only probability group in NWS TAFs; PROB40, a 40 percent chance, can appear in military and international TAFs (Aviation Weather Handbook, p. 27-17).

TEMPO and PROB30 groups never carry vicinity weather or wind shear (Aviation Weather Handbook, pp. 27-16 to 27-17).

What about BECMG? The handbook doesn't list it among the NWS change indicators (Aviation Weather Handbook, p. 27-15). It appears only in the handbook's examples of the different TAF format used at some joint civil-military airports, which also give visibility in meters (Aviation Weather Handbook, p. 27-17). If you meet one, check how your weather source explains it before relying on it.

Worked example: find the flight window

The forecast below is our own practice example, built to the handbook's format. No forecaster issued it, so don't read it as a real Omaha TAF; it isn't copied from FAA material either. You can paste it, or any other TAF, into our free METAR and TAF decoder to see each group spelled out.

TAF KOMA 121120Z 1212/1312 17009KT P6SM FEW040 SCT250 FM121700 20015G25KT P6SM SCT050 BKN120 PROB30 1221/1224 3SM TSRA BKN035CB FM130000 32012KT 5SM -SHRA BR BKN015 OVC030 TEMPO 1302/1305 2SM SHRA BR OVC009 FM130800 33008KT P6SM SCT025

Issued on the 12th at 1120 UTC and valid for 24 hours from 1200 UTC, it lays out the day like this:

1. 1200 to 1700 UTC on the 12th: 170° at 9 knots, more than 6 miles, a few clouds at 4,000 feet and scattered cloud at 25,000.
2. From 1700 UTC: 200° at 15 knots with gusts to 25, more than 6 miles, scattered at 5,000 feet and broken at 12,000. From 2100 UTC to midnight, a thunderstorm with rain is possible (30 percent), with 3 miles of visibility and broken cumulonimbus at 3,500 feet.
3. From 0000 UTC on the 13th: 320° at 12 knots, 5 miles in light rain showers and mist, broken at 1,500 feet and overcast at 3,000. Between 0200 and 0500 UTC, spells of 2 miles in rain showers and mist under an overcast at 900 feet. The TEMPO group gives no wind, so 320° at 12 knots still applies.
4. From 0800 UTC: 330° at 8 knots, more than 6 miles and scattered cloud at 2,500 feet, until the TAF ends at 1200 UTC.

Planning the flight. Say your clock runs 5 hours behind UTC. Then 1200 to 1700 UTC is 7 a.m. to noon local, with light wind and good visibility: the best window in this forecast. From noon the gusts reach 25 knots, so check them against your aircraft's wind and gust limits, which FAA guidance encourages manufacturers to provide (AC 107-2A, para. 8.12.2.5.1). Take the PROB30 seriously and plan to be packed up before 2100 UTC, which is 4 p.m. local. The overnight TEMPO spells bring 2 miles of visibility, below the 3-mile minimum, so you couldn't fly in them, and their 900-foot overcast would also hold you to 400 feet AGL or lower to keep 500 feet beneath it (14 CFR 107.51). The last period, from 0800 UTC, looks good again.

Before you rely on a TAF

• Check whether an amended TAF has replaced the one you read.
• Remember the 5-mile area. The farther your site is from the runways, the more it can differ.
• Compare the forecast with the latest METAR, which reports what is actually happening at the airport.
• Convert every time from UTC, including the FM, TEMPO and PROB30 times.
• Read TEMPO and PROB30 groups as additions to the main forecast, not replacements for it.

Practice until it's automatic

Our free Part 107 weather questions include TAF groups with full explanations, and the free 20-question practice test mixes weather with every other topic. For more, Part 107 Complete ($39, one-time) includes a weather trainer that decodes any METAR or TAF you paste and drills you on one report at a time, plus timed mock exams. If a code trips you up, the Part 107 glossary can help, and our guide to reading a METAR covers the weather and cloud codes TAFs share.

Questions people ask

How far from the airport does a TAF apply?

A TAF forecasts conditions within 5 statute miles of the center of the airport's runway complex. Weather farther away may be different (Aviation Weather Handbook, p. 27-6).

What is the difference between FM and TEMPO in a TAF?

FM starts a new, complete forecast that replaces everything before it. TEMPO describes temporary spells, each lasting an hour or less and together covering less than half of the stated period, and lists only the elements that change (Aviation Weather Handbook, pp. 27-15 to 27-16).

What does PROB30 mean?

PROB30 is a 30 percent chance of a thunderstorm or precipitation event during the stated hours. It is the only probability group National Weather Service TAFs use (Aviation Weather Handbook, p. 27-17).

Does a TAF include the temperature?

No. National Weather Service TAFs don't include a temperature forecast (Aviation Weather Handbook, p. 27-6).