... Code Talking about Aviation weather (Ugh!) ...

OBJECTIVES:

• How to decode METAR?

What is a METAR?

A METAR is a coded weather observation issued on a regular basis by meteorological offices.
The acronym METAR stands for METeorological Aerodrome Report and is thus related to the weather of a specific airport at the specified time of observation.

METAR (and SPECI, see further) shall contain the following elements in the order indicated:

• identification of the type of report;
• location indicator;
• time of the observation;
• identification of an automated or missing report, when applicable;
• surface wind direction and speed;
• visibility;
• runway visual range, when applicable;
• present weather;
• cloud amount, cloud type (only for cumulonimbus and towering cumulus clouds) and height of cloud base (AGL) or, where measured, vertical visibility;
• air temperature and dew-point temperature; and
• QNH and, when applicable, QFE (QFE included only in local routine and special reports),
• followed eventually by specific remarks.

What is a SPECI?

A SPECIal report is basically an abbreviated METAR which is issued whenever weather conditions fluctuate about or are about below specified minima. They are recognisable by the time of issue which is out of sequence compared with the regular METAR report.

What does AUTO mean?

An AUTOmatic report is distinguished by the word AUTO inserted behind the date/time group. Automatic reports are generally regarded as less accurate.

What does TAF mean?

A TAF is a Terminal Area Forecast. As it's name implies, it is a weather prediction rather than an observation.
Aerodrome forecasts and amendments thereto shall be issued as TAF and include the following information in the order indicated:

• identification of the type of forecast;
• location indicator;
• time of issue of forecast;
• identification of a missing forecast, when applicable;
• date and period of validity of forecast;
• identification of a cancelled forecast, when applicable;
• surface wind;
• visibility;
• weather;
• cloud; and
• expected significant changes to one or more of these elements during the period of validity.

In the further explanation and examples the most common specifications and weather phenomena are used. For the full details one could look up the relevant documentation as available in the professional circuits:)

A SPECI message is identical to a METAR but is established punctually instead of regularly. It is a special observation message highlighting any significant change since the last METAR or SPECI was issued.

A TAF is a terminal forcast. It is issued every few hours, and is updated if necessary sooner.

METAR explained

Example:

METAR	KRNO	210056Z	05012KT	10SM	-SN	BKN050	02/M08	A3016	RMK AO2 SLP228	T00221083
1	2	3	4	5	6	7	8	9	10	11

1. Message Type:

• METAR: routine weather report
• SPECI: special weather report, triggered by a weather change
• AUTO will be first item for ASOS/AWOS generated reports

2. ICAO Identifier (4-letter)

3. Issuance Time DDHHMMz (UTC)

4. Wind

• First 3 digits: True Wind direction or average if variable (VRB).

Note: If the wind direction varies 60° or more, the direction will be indicated with a V (e.g. 180V250)

• Next 2 digits: Mean speed and units
• Next 2 digits: Mean speed and units

• G (gust) as needed – 2 or 3 digit maximum speed
• Calm will be indicated by 00000KT
• Example: 18012G22KT 150V240

5. Horizontal Visibility

• Statue miles (SM) and fractions (US & Canada only) or,
• 4 digit minimum visibility in meters, and,
• Lowest value and direction, as required (shown as a remark)

Qualifier				Weather Phenomena
Intensity or Proximity		Descriptor		Precipitation		Obscuration		Other
-	Light	BC	Patches	DZ	Drizzle	BR	Mist (1)	DS	Duststorm
		BL	Blowing (2)	GR	Hail (3)	DU	Widespread Dust
No qualifier	Moderate	DR	Low Drifting (4)	GS	Small Hail and/or snow pellets (5)	FG	Fog (6)	FC	Funnel Clouds
		FZ	Freezing	IC	Ice Crystals	FU	Smoke	PO	Dust/Sand Whirls
+	Heavy	MI	Shallow	PL	Ice Pellets	HZ	Haze	SQ	Squall(s)
		PR	Partial	RA	Rain	SA	Sand
VC	Vicinity (7)	SH	Shower(s)	SG	Snow Grains	VA	Volcanic Ash	SS	Sandstorm
		TS	Thunderstorm	SN	Snow
				UP	Unknown Precipitation
(1) Visibility at least 1000m (5/8SM) but not more than 9600m (6SM) (2) 6 feet or more above the ground (3) Hailstone diameter 5mm or greater (4) Less than 6 feet above the ground (5) Hailstone diameter less than 5mm (6) Visibility less than 1000m (5/8SM) (7) Within 8KM (5SM) of the aerodrome but not at the aerodrome

7. Sky Cover ABOVE GROUND LEVEL (AGL)

Cloud Description:

• Amount in eights (octas)
• SKC=Sky Clear (clear below 12,000 for ASOS/AWOS)
• NSC=No significant clouds
• FEW=Few (1/8 to 2/8 sky cover)
• SCT=Scattered (3/8 to 4/8 sky cover)
• BKN=Broken (5/8 to 7/8 sky cover)
• OVC=Overcast (8/8 sky cover)

Example: BKN050 means cloud condition is broken at 5000 feet above ground level (agl)

8. Temperature/Dewpoint (whole °C) (preceded by M=minus)

• First 2 digits = temperature
• Second 2 digits = dewpoint

9. Altimeter setting (QNH) and indicator (A=InHg, Q=hPa)

10. Supplementary Information

• RE = Recent weather followed by weather codes
• WS = Windshear, followed by:
• TKOF/LDG (takeoff/landing)
• RWY (2 digits runway identifier and designator L/R/C)
• RMK = Remark
• SLP = Sea Level Pressure
• T00221083 (Expanded temp/dewpoint)

1st, 5th digits: 0=plus, 1=minus

2nd-4th digits: temp (decimal missing) (02.2)

6th-8th digits: dewpoint (decimal missing) (-8.3)

11. Trend Forecast (2 hours from time of observation) (Not used in US)

• PROB and 2 digits (30 or 40) = probability 30% or 40%
• Used to indicate the probability of occurance of alternate element(s) or temporary fluctuations
• Change Indicator
• BECMG = Becoming (used where changes are expected to reach or pass through specified values)
• TEMPO = Temporary (fluctuations of less than one hour duration)
• NOSIG = No significant change

• Forecast Wind (same as item 4)
• Forecast Visibility (as item 5) (9999 indicates 10Kilometers vis or greater)
• Forecast Weather (as item 6)
• Forecast Cloud (as item 7)

Eight Figure Group

The first two digits correspond to the runway designator. For parallel runways LEFT is indicated by the designator only (18L would be displayed as 18) and RIGHT has 50 added (18R would be displayed as 68). When all runways are affected the figure group 88 will be used. If 99 appears as the first two digits the information is a repetition of the last message because no new message has been received in time for transmission.Runway Deposits

Note: The quoted depth is the mean of a number of reading or if operationally significant the greatest depth measured.

Friction Coefficient or Braking Action (7th and 8th digits)
28	Friction coefficient 0.28
35	Friction coefficient 0.35
91	Braking action poor
92	Braking action medium to poor
93	Braking action medium
94	Braking action medium to good
95	Braking action good
99	Figures unreliable
//	Braking action not reported or runway not operations or airport closed.

Note: Where braking action is assessed at a number of points along the runway the main value will be transmitted or if operationally significant the lowest value. If measuring equipment does not allow measurement of friction with satisfactory reliability (such as contaminated by wet snow, slush or loose snow) the figure 99 will be used.

Automated Surface/Weather Observation System (ASOS/AWOS)

Note: FAA only.

The Automated Surface Observation System (ASOS) and Automated Weather Observation System (AWOS) observe and report altimeter setting, wind direction and speed, temperature, dewpoint, visibility and ceiling/cloud height. Pilots may use automated weather observation from ASOS/AWOS, provided the observations from ASOS/AWOS, provided the observation includes all necessary weather parameters, and that the system is installed, operated and maintained according to applicable FAA standards.

Pilots may obtain the ASOS/AWOS reports through written, radio or telephone methods. Refer to METAR section for ASOS/AWOS report format.

ASOS/AWOS observations may not be used as an authorized weather observation if either the visibility or the wind is reported as missing.

ASOS/AWOS observation are unusable for the purpose of initiating or conducting an instrument approach if the altimeter setting is reported as missing unless an approved alternate source is noted on the applicable approach chart.

TAF explained

Example:

TAF	KRNO	202320Z	210024	04010G20KT	P6SM	-SN	SCT060
1	2	3	4	5	6	7	8

FM0300	05008KT	P6SM	SCT060
9

1. Type of report (TAF)

2. ICAO Identifier (4 letter)

3. Issuance time (DDHHMMZ) UTC. May precede ICAO identifier at some airports.

4. Day (DD). Hour begins (1st two digits XX) Hour ends (2nd two digits).

5. Wind. First 3 digits true wind direction or average if variable. If the wind varies 60° or more, the direction will be indicated with a V (e.g. 120V190). Next two digits Mean speed and units (KT=knots, KMH=kilometers per hour, or MPS=meters per second). G=gust as needed (2 or 3 digits). Calm will be indicated by 00000XXX (XXX will be replaced by the appropriate units).

6. Horizontal visibility.

a. Prevailing visibility (PV)

b. Runway Visual Range (RVR)

• R=Runway Designator, L/R/C as needed, “/”
• P/M=Plus/Minus (US Only)
• 4 digit value (feet/meters)
• V(variability) with tendency U/D/N (up/down/no change)

7. Present Weather (constructed sequentially):

• Intensity
• Descriptor
• Precipitation (Dominant type is listed first if more than one type reported)
• Obscuration
• Other

Qualifier				Weather Phenomena
Intensity or Proximity		Descriptor		Precipitation		Obscuration		Other
	Light	BC	Patches	DZ	Drizzle	BR	Mist (1)	DS	Duststorm
		BL	Blowing (2)	GR	Hail (3)	DU	Widespread Dust
No qualifier	Moderate	DR	Low Drifting (4)	GS	Small Hail and/or snow pellets (5)	FG	Fog (6)	FC	Funnel Clouds
		FZ	Freezing	IC	Ice Crystals	FU	Smoke	PO	Dust/Sand Whirls
+	Heavy	MI	Shallow	PL	Ice Pellets	HZ	Haze	SQ	Squall(s)
		PR	Partial	RA	Rain	SA	Sand
VC	Vicinity (7)	SH	Shower(s)	SG	Snow Grains	VA	Volcanic Ash	SS	Sandstorm
		TS	Thunderstorm	SN	Snow
				UP	Unknown Precipitation
(8) Visibility at least 1000m (5/8SM) but not more than 9600m (6SM) (9) 6 feet or more above the ground (10)Hailstone diameter 5mm or greater (11)Less than 6 feet above the ground (12)Hailstone diameter less than 5mm (13)Visibility less than 1000m (5/8SM) (14)Within 8KM (5SM) of the aerodrome but not at the aerodrome

8. Sky Cover

• Cloud Description
• Amount in eights (octas)

• Height: 100s of feet (30m)
• Type CB (Cumulonimbus) or TCU (Towering cumulus) only.

• Visibility is 10KM or greater
• No CB and no cloud below 1500M (5000ft) or below highest minimum sector altitude whichever is greater, and
• No precipitation, thunderstorm, sandstorm, duststorm, shallow fog, or low drifting dust/sand/snow.

Vertical visibility (when sky obscured) – VV100’s of feet (30m) (VV /// means vertical visibility unavailable)

Optional groups (Forecast icing, Turbulence, & Temperature)

T= Temperature group indicator

Temperature: two digits (if below 0°, will be preceded by “M”),”/”

Expected time temperature will be reached: 2 digits, Z.

Icing Layer(s): 6 digits for each icing group (6WXXXY).

6: first digit of the icing group is always a 6.

Icing type: Second digit:

	Icing Intensity	Location
0	None	None
1	Light Icing
2	Light Icing	In cloud
3	Light Icing	In precipitation
4	Moderate
5	Moderate	In cloud
6	Moderate	In precipitation
7	Severe
8	Severe	In cloud
9	Severe	In precipitation

Icing layer’s base: next 3 digits. (direct reading in 100s of ft/30s meters)

Thickness of icing layer: last digit:

	Thickness of Layer
0	Up to top of cloud
1	300m/1000’
2	600m/2000’
3	900m/2000’
4	1200m/4000’
5	1500m/5000’
6	1800m/6000’
7	2100m/7000’
8	2400m/8000’
9	2700m/9000’

Turbulence Layer(s): 6 Digits (5WXXXY)

5: first digit of the turbulence group is always a 6.

Turbulence type: Second digit:

	Intensity	Weather Condition	Frequency
0	None
1	Light
2	Moderate	Clear	Occasional
3	Moderate	Clear	Frequent
4	Moderate	Cloud	Occasional
5	Moderate	Cloud	Frequent
6	Severe	Clear	Occasional
7	Severe	Clear	Frequent
8	Severe	Cloud	Occasional
9	Severe	Cloud	Frequent

Turbulence layer’s base: next 3 digits. (direct reading in 100s of ft/30s meters)

Thickness of turbulence layer: last digit:

	Thickness of Layer
0	Up to top of cloud
1	300m/1000’
2	600m/2000’
3	900m/2000’
4	1200m/4000’
5	1500m/5000’
6	1800m/6000’
7	2100m/7000’
8	2400m/8000’
9	2700m/9000’

Significant Changes In Forecast

1. Probability groups(s)

• PROB and 2 digits (30 or 40).
• Probability 30% or 40% used to indicate the probability of occurrence of alternate element(s) or temporary fluctuations. (US will only use 40%). May also be listed as TEMPO by some non US weather services.
• TIME (beginning 2 digits, ending 2 digits)
• Forecast weather phenomena.

2. Forecast Change

Indicators

• BCMG=Becoming (used when changes are expected to reach or pass through specified values)
• FM = From and 2 digit time
• TO = To and 2 digit time
• TEMPO = Temporary fluctuation
• Forecast weather phenomena.

AIRMETs

Hazardous weather advisories of moderate intensity will be issued as AIRMETs. AIRMETs are issued when the following conditions are expected to cover an area of at least 3000 square miles:

Moderate icing.

Moderate turbulence.

Sustained surface winds of 30 knots or more.

Ceilings less than 1,000 ft. and/or visibility less than 3 miles affecting 50% of an area at one time.

Extensive mountain obscuration.

SIGMET's

Hazardous weather advisories of severe intensity will be issued as SIGMETs. SIGMETs are reported as convective or nonconvective.

Convective SIGMETs report only thunderstorms and related phenomena (tornadoes, heavy precipitation, hail and high surface winds.

Nonconvective SIGMETs are issued when the following conditions occur or are expected to cover an area of at least 3,000 square miles:

Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms.

Severe icing not associated with thunderstorms.

Widespread duststorms, sandstorms, or volcanic ash lowering surface or inflight visibilities to below three miles.

Volcanic eruption.

Volcanic eruption SIGMET's are identified by an alphanumeric designator which consists of an alphabetic identifier and issuance number. The first time an advisory is issued for a phenomenon associated with a particular weather system, it will be given the next alphabetic designator in the series and will be numbered as the first for that designator. Subsequent advisories will retain the same alphabetic designator until the phenomenon ends. In the conterminous U.S., this means that a phenomenon that is assigned an alphabetic designator in one area will retain that designator as it moves within the area or into one or more other areas. Issuance’s for the same phenomenon will be sequentially numbered, using the same alphabetic designator until the phenomenon no longer exists. Alphabetic designators NOVEMBER through YANKEE, except SIERRA and TANGO are only used for SIGMET's, while designators SIERRA, TANGO and ZULU are used for AIRMET's

Pilot Weather Report (PIREP)

Pilots must report any significant weather or flight condition to ATC as soon as possible. Additionally, all significant weather or flight conditions that clearly differ from the forecast should be reported to Dispatch. There is no specific format for this type of report.

NOTE: Report windshear encountered during departure or approach to the tower controller as soon as possible. Use the term “PIREP” to ensure that it is rebroadcast.

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Module Manager e-mail: .............................

Contributing Author(s)/Support:

• Splendor Bouman
• Carl Stallone

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