How to read aviation weather reports: METAR, TAF, SIGMET, AIRMET and PIREP

Turbulence is never left to chance: before every departure, and throughout the flight, crews check a set of standardised weather messages: METAR, TAF, SIGMET, AIRMET and PIREP. Their abbreviated format can look impenetrable, but each one answers a specific question. This article explains what each one tells you and how to read it.

METAR: current conditions at the airport

A METAR is a coded report of conditions at an airport: wind, visibility, present weather, cloud, temperature and pressure (Met Office). It is issued routinely, usually every 30 or 60 minutes depending on the airport and the weather service. In Estonia, for example, Tallinn airport issues one every half hour and Ämari air base one every hour (Estonian AIP).

Example METAR, written for this article:

METAR LEMD 171230Z 24015G25KT 9999 FEW040 18/09 Q1012

Each group is decoded following the Hong Kong Observatory guide (HKO).

TAF: the airport forecast

A TAF is the forecast for a specific airport. Most cover 24 to 30 hours, are issued four times a day and are amended when conditions change significantly (SKYbrary).

Example TAF, written for this article:

TAF LEMD 171100Z 1712/1818 24012KT 9999 FEW040
PROB30 TEMPO 1715/1718 24020G32KT TSRA
BECMG 1800/1802 18008KT

BECMG (becoming), TEMPO (temporarily) and PROB (probability) follow the Hong Kong Observatory TAF guide (HKO).

A SIGMET, decoded

A SIGMET warns of hazardous weather en route. The example below is fictitious: it follows the ICAO format and uses the sample indicators (YUCC, YUDO) from ICAO’s regional SIGMET guide (ICAO).

YUCC SIGMET 2 VALID 101200/101600 YUDO–
YUCC AMSWELL FIR SEV TURB FCST AT 1200Z
N OF S2000 FL300/380 MOV E 20KT NC=

Only a handful of phenomena can trigger a SIGMET, and all of them matter (ICAO):

• Thunderstorms hidden in other cloud, frequent or in a line
• Tropical cyclones
• Severe turbulence
• Severe icing
• Severe mountain waves
• Heavy dust or sandstorms
• Volcanic ash
• Radioactive cloud

A SIGMET is valid for up to 4 hours, except for tropical cyclones and volcanic ash, where it can be valid for up to 6 hours (FAA).

AIRMET: moderate-intensity weather

Some national or regional systems use AIRMETs to report weather that can affect light aircraft or lower-level flights, such as moderate turbulence, icing or mountain waves. The definition and coverage are not the same everywhere. Under the ICAO definition, for example, it refers to flights below about 10,000 feet, or 15,000 in mountainous areas (SKYbrary). In the United States, AIRMETs explicitly include moderate turbulence and are updated every 6 hours (FAA).

PIREP: the view from the cockpit

A PIREP reports the actual conditions an aircraft meets in flight. Under FAA rules, each report must give position, time, altitude and aircraft type, plus at least one observed phenomenon; for turbulence or icing reports the aircraft type is always mandatory (FAA). PIREPs go to air traffic control, weather services and other crews, and can be used to correct a forecast or trigger a warning (SKYbrary).

Example PIREP in US format, written for this article:

UA /OV BIS270030 /TM 1445 /FL350 /TP B738 /TB MOD

The structure follows the FAA manual for these reports (FAA).

When they meet moderate or severe turbulence, crews may be required, depending on the jurisdiction and the operator’s procedures, to issue a special air-report. ICAO sets technical thresholds for these reports based on the turbulence intensity measured by the aircraft’s own sensors (ICAO), and they are one of the main ways crews contribute to SIGMET information (Transport Malta).

Frequently asked questions

Before your flight, check your route on IsItBumpy to see official warnings and the turbulence forecast stage by stage. And if you have a METAR or TAF to hand, you can decode it with our translator.

The examples in this article are fictitious and for teaching purposes only. For your flight, check the real data on IsItBumpy and always follow your crew’s instructions.