What is METAR and how to decode it?
In Aviation, weather plays a very important role in the day to day operations. In fact, a pilot needs to check the weather several times during the different phases of flight. Before the airplane is ready to leave the gate, he/she always checks the weather at the arriving and departing aerodrome in the pre-flight briefing. If they feel that the weather at and around the airport is not suitable for flying, they might decide not to operate the flight or even divert to their alternate aerodrome.
In aviation, the weather information of an aerodrome is broadcasted in a report called METAR (Meteorological Aerodrome Report). They are published in a fixed format which is common all over the world.
METAR is a string of abbreviations which denote various weather conditions around the aerodrome. You can learn all the METAR Abbreviations by referring to this document. With the help of this document, let us take an example of METAR of Chennai International Airport and decode it!
Eg: VOMM 131530Z 16006KT 4000 HZ SCT020 FEW025TCU BKN100 30/23 Q1009 NOSIG
Abbreviation
|
Indicates
|
Meaning
|
VOMM
|
ICAO Code
|
Chennai Intl Airport
|
131530Z
|
Date and Time
|
13 - Day of the month. 1530Z - Time of observation.
|
16006KT
|
Wind Direction
|
Wind direction is from 160 deg at 06 knots (denoted in Meters per second in Metric)
|
4000
|
Visibility
|
Prevailing Visibility at the airport is 4 km or 4000m
|
HZ
|
Weather Condition
|
Haze
|
SCT020
|
Cloud condition
|
Scattered clouds present at 2000ft
|
FEW025TCU
|
Cloud Condition
|
Few clouds present at 2500ft in towering cumulus form
|
BKN100
|
Cloud Condition
|
Broken clouds present at 10,000ft above aerodrome level
|
30/23
|
Temperature and Dew Point
|
The temperature at the airport is 30 deg. Dewpoint is 23 deg
|
Q1009
|
Sea Level Pressure / Barometer setting QNH
|
1009 hectopascals ( denoted in inch of Mercury - inHg in FAA)
|
NOSIG
|
Remark
|
No significant change in weather for the next 2 hours
|
SPECI Reports:
A SPECI is a special report of meteorological weather conditions which is issued when one or more conditions match the specified criteria significant to aviation operations. It is also used to identify reports which are recorded ten minutes after an improvement to the SPECI conditions.
SPECI Example: SPECI VMMC 242341Z 10010KT 3500N VCSH FEW010 SCT018 BKN070 28/26 Q1004 TEMPO 5000 SHRA
SPECI Criteria :
Element
|
Criteria
|
Wind Direction
|
Direction changed by 30 deg when the average speed is 20 KT or more.
|
Wind Speed
|
Speed changed by 10 KT when the average speed is 30 KT or more
|
Wind Gusts
|
Gust speed exceeds by 10 KT than the last reported speed
|
Visibility
|
When prevailing visibility is below the minimum operable limit of the aerodrome
|
Weather Phenomenon
|
When any of the weather phenomena such as thunderstorms, hail storms, sandstorms, dust storms, etc are reported in high intensity.
|
Cloud
|
When cloud cover (broken or overcast) is below the minimum operable limit of the aerodrome.
|
Temperature
|
When temperature increases or decreases by 5 deg since the last reported temperature
|
Pressure
|
When pressure increases or decreases by 2 hPa since the last reported pressure
|
Remarks
|
If the pilots repeatedly report wind shear or other such weather phenomena
|
Thank you for reading!
