Rule 39C

METAR/ SPECI (Aircraft General Knowledge) | METAR/ SPECI


METAR/ SPECI

What is METAR (Meteorological Aviation Report)? (To prepare for RTR(A) part 2 and also useful info for met paper)

Aviation Weather Report (METAR/SPECI)

METAR is a format for reporting weather information. A METAR weather report is predominantly used by pilots in fulfillment of a part of a pre-flight weather briefing, and by meteorologists, who use aggregated METAR information to assist in weather forecasting.

Raw METAR is the most common format in the world for the transmission of observational weather data. It is highly standardized through the International Civil Aviation Organization (ICAO), which allows it to be understood throughout most of the world.

or

METAR is an aviation routine weather report issued at hourly or half-hourly intervals. It is a description of the meteorological elements observed at an airport at a specific time.

SPECI is an aviation special weather report issued when there is significant deterioration or improvement in airport weather conditions, such as significant changes of surface winds, visibility, cloud base height and occurrence of severe weather. The format of the SPECI report is similar to that of the METAR and the elements used have the same meaning. The identifier METAR or SPECI at the beginning of the weather report differentiates them.

The aviation weather report also includes a section containing the trend forecast, which indicates the forecast change in meteorological conditions in the next two hours.

Information contained in a METAR

A typical METAR contains data for the temperature, dew point, wind speed and direction, precipitation, cloud cover and heights, visibility, and barometric pressure. A METAR may also contain information on precipitation amounts, lightning, and other information that would be of interest to pilots or meteorologists such as a pilot report or PIREP, colour states and runway visual range (RVR).

In addition, a short period forecast called a TREND may be added at the end of the METAR covering likely changes in weather conditions in the two hours following the observation. These are in the same format as a Terminal Aerodrome Forecast (TAF).

The complement to METARs, reporting forecast weather rather than current weather, are TAFs. METARs and TAFs are used in VOLMET broadcasts.

Cloud reporting

Cloud coverage is reported by the number of ‘oktas’ (eighths) of the sky that is occupied by cloud.

This is reported as:

Abbreviation Meaning
SKC “No cloud/Sky clear” used worldwide but in North America is used to indicate a human generated repor
CLR “No clouds below 12,000 ft (3,700 m) (U.S.) or 10,000 ft (3,000 m) (Canada)”, used mainly within North America and indicates a station that is at least partly automated
NSC “No (nil) significant cloud”, i.e., none below 5,000 ft (1,500 m) and no TCU or CB. Not used in North America.
FEW “Few” = 1–2 oktas
SCT “Scattered” = 3–4 oktas
BKN “Broken” = 5–7 oktas
OVC “Overcast” = 8 oktas, i.e., full cloud coverage
VV Clouds cannot be seen because of fog or heavy precipitation, so vertical visibility is given instead.
METAR WX codes

METAR abbreviations used in the WX section. Remarks section will also include began and end times of the weather events.

Codes before remarks will be listed as “-RA” for “light rain”. Codes listed after remarks may be listed as “RAB15E25” for “Rain began at 15 minutes after the top of the last hour and ended at 25 minutes after the top of the last hour.”

Type Abbreviation Meaning Abbreviation Meaning
Intensity Light intensity blank Moderate intensity
Intensity + Heavy intensity VC In the vicinity
Descriptor MI Shallow PR Partial
Descriptor BC Patches DR Low drifting
Descriptor BL Blowing SH Showers
Descriptor TS Thunderstorm FZ Freezing
Precipitation RA Rain DZ Drizzle
Precipitation SN Snow SG Snow Grains
Precipitation IC Ice Crystals PL Ice Pellets
Precipitation GR Hail GS Small Hail and/or Snow Pellets
Precipitation UP Unknown Precipitation
Obscuration FG Fog VA Volcanic Ash
Obscuration BR Mist HZ Haze
Obscuration DU Widespread Dust FU Smoke
Obscuration SA Sand PY Spray
Other SQ Squall PO Dust or Sand Whirls
Other DS Duststorm SS Sandstorm
Other FC Funnel Cloud
Time B Began At Time E Ended At Time
Time 2 digits Minutes of current hour 4 digits Hour/Minutes Zulu Time

 

 

e.g

The latest aviation weather report at the Ahmedabad International Airport issued by the Ahmedabad Observatory at 15:30 LT on 13 Jul 15METAR VAAH 130730Z 35005KT 310V050 9999 FEW025 34/25 Q1000 NOSIG=

Decoded METAR/SPECI in plain language:-

Aviation weather report (METAR) at 0730 UTC on 13 Jul 2015 issued by the Ahmedabad Observatory :

Wind Visibility Weather Cloud Amount Cloud Base Temperature Dew Point Pressure(QNH)
5 knots from 350 degrees (N), variability: 310-050 degrees
10 km or above
No significant weather
1 to 2 oktas
2500 feet
34 oC
25 oC
1000 hPa
Next Two Hours Change
No Significant Change
Visibility: As a result of an amendment by the International Civil Aviation Organization starting from 1 November 2001, the night-time visibility for aviation purpose represents the greatest distance at which light in the vicinity of 1 000 candelas can be seen and identified against an unlit background.  As it is made specifically for aviation purpose, it may occasionally differ from the night-time visibility for general purpose which represents the degree of atmospheric transparency and is independent of the intensity of lights being observed.
okta(s): the international unit for reporting cloud amount. Cloud amount is assessed in total which is the estimated total apparent area of the sky covered with cloud.
1 okta is one-eighth of sky covered with cloud. 0 okta = sky clear, 1-2 oktas = few, 3-4 oktas = scattered, 5-7 oktas = broken and 8 oktas = overcast.
QNH: the pressure value measured at airport with adjustment made to suit aeronautical use.
METAR/ SPECI

Weather

 

 

 

 

 

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