Weather observations (METAR)

In this post I’m going to look at each element of METAR and SPECI weather reports.

What is a METAR?

A METAR weather report is a routine aviation weather report taken between the 50 minute mark and before the next hour. It is a surface observation of an airport.

What is a SPECI?

A SPECI report is an unscheduled weather report taken outside of normal METAR times. A SPECI report may be issued when the following occur:

Wind Shift- wind direction changes by 45 degrees or more, in less than 15 minutes and the wind speed is 10kts or more throughout the shift.

Visibility- Surface visibility decreases to less than, or if below increases to equal or exceed,
3 miles
2 miles
1 mile
Lowest instrument approach procedure minimum published in FAA’s Instrument Flight Procedures Information Gateway. If none 1/2SM.

RVR (Runway Visual Range)- Highest value decreases to less than, or if below increases to equal or exceed, 2,400’ during the preceding 10 minutes.

Tornado, Funnel Cloud, or Waterspout- Is observed. Disappears from sight or ends.

Thunderstorm- Begins or ends

Precipitation- Hail begins or ends. Freezing precipitation begins, ends, or changes intensity. Ice pellets begin, end, or change intensity.

Squalls- When squall occurs.

Ceiling- Forms or dissipates below, decreases to less than, or if below increases to equal or exceed:
3,000’
1,500’
1,000’
500’
Lowest instrument approach procedure minimum published in FAA’s Instrument Flight Procedures Information Gateway. If none 200’.

Sky Condition- A layer of clouds or obscurations aloft is present below 1,000’ and no layer below 1,000’ reported in previous report.

Volcanic Eruption- When it is first noted.

Aircraft Mishap- Upon notification

Misc- Any other meteorological situation designated critical in the opinion of the reporter.

Reports Decoded

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

Reports start with the type report METAR or SPECI

Station Identifier

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

Identifies the station, in ICAO format, to which the report applies.

Date and Time

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

This field shows the time the observation was taken. The first 2 digits indicate day of the month (01). That is followed by the hour and minute (1955). The time is always followed by Z for UTC (Coordinated Universal Time).

Report Modifier

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

This field indicates the observation was fully automatic with no human intervention or oversight. Corrected reports have the modifier COR. Manual reports do not have this field.

Wind Group

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

The first 3 digits is the direction the wind is coming from. This wind, 220, is coming from the southwest and heading northeast.
Determined by averaging wind direction over a 2 minute period

Next in 2 or 3 digits is wind speed calculated over a 2 minute period. Followed by KT to indicate it’s reported in knots. Some countries use kilometers per hour KPH or meters per second MPS.

Wind gusts are determined over the most recent 10 minute period. Defined as rapid fluctuations in wind speed with a variation of 10kts or more between peaks and lulls.

Variable wind direction is considered when in a 2 minute evaluation period the wind speed was 6kts or less. The wind would be coded as VRB in place of wind direction. For example VRB03KT.
Wind may also be considered Variable when, in the eval period, wind direction varies by 60 degrees or more and speed is greater than 6kts. The wind would be modified as 22015 180V250.

Calm Wind when no motion of air is detected wind is reported as calm and coded as 00000KT.

Visibility

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

Visibility is the opacity of the atmosphere. It is measured in statute miles (5,280’). This is reminded by the SM seen after the visibility in the report.
Stations report either prevailing visibility at manual stations or visibility determined from sensors at automated stations.

Prevailing visibility is the greatest distance seen throughout at least 180 degrees of view not necessarily continuously.

Runway Visual Range (RVR)

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

RVR is reported when visibility is 1SM or less and/or RVR for the designated instrument runway is 6,000’ or less. Otherwise RVR is omitted from the report.

RVR is coded as follows. Initial R stands for Runway and is followed by the runway number (R17L, runway 17L). Next is a solidus / followed by visual range in feet. Example R17L/2600FT, Runway 17L visibility 2,600FT.

In the US RVR values are coded in increments of 100’ up to 1,000’. Increments of 200’ from 1,000’ to 3,000’. Increments of 500’ from 3,000’ to 6,000’.

In the US the touchdown zones RVR is reported. When multiple runways are in use the lowest one is reported.

RVR may be reported as variable. For example over 10 minutes runway 01L varying between 600’ and 1,000’ would be coded as R01L/0600V1000FT

If RVR is less than lowest reportable value the group is preceded by M. For example R01L/M0600FT.

Present Weather Group

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

Present weather includes precipitation, obscurations, and other weather phenomena.
The different modifiers are in this table

The intensity qualifiers are light, moderate, and heavy. They are coded with precipitation types, except ice crystals (IC) and hail (GR), including those associated with a thunderstorm (TS) and those of a showery nature (SH). Tornadoes and waterspouts are coded as heavy (+FC). No intensity is ascribed to the obscurations of blowing dust (BLDU), blowing sand (BLSA), and blowing snow (BLSN). Only moderate or heavy intensity is ascribed to sandstorm (SS) and duststorm (DS).
When more than one form of precipitation is occurring at a time, or precipitation is occurring with an obscuration, the reported intensities are not cumulative. The reported intensity will not be greater than the intensity for each form of precipitation. For example, -FZRAPL is light freezing rain and light ice pellets, not light freezing rain and moderate ice pellets.

Weather phenomena occurring beyond the point of observation (between
5 and 10 sm) are coded as in the vicinity (VC). VC can be coded in combination with thunderstorm (TS), fog (FG), shower(s) (SH), well-developed dust/sand whirls (PO), blowing dust (BLDU), blowing sand (BLSA), blowing snow (BLSN), sandstorm (SS), and duststorm (DS). Intensity qualifiers are not coded in conjunction with VC.
For example, VCFG can be decoded as meaning some form of fog is between 5 and 10 sm of the point of observation. If VCSH is coded, showers are occurring between 5 and 10 sm of the point of observation.

Descriptors are qualifiers that further amplify weather phenomena and are used in conjunction with some types of precipitation and obscurations. The descriptor qualifiers are: shallow (MI), partial (PR), patches (BC), low drifting (DR), blowing (BL), shower(s) (SH), thunderstorm (TS), and freezing (FZ).
Only one descriptor is coded for each weather phenomena group (e.g., FZDZ).
The descriptors shallow (MI), partial (PR), and patches (BC) are only coded with fog (FG) (e.g., MIFG). Mist (BR) is not coded with any descriptor.
The descriptors low drifting (DR) and blowing (BL) will only be coded with dust (DU), sand (SA), and snow (SN) (e.g., BLSN or DRSN). DR is coded with DU, SA, or SN for raised particles drifting less than 6 ft above the ground.
When blowing snow is observed with snow falling from clouds, both phenomena are reported (e.g., SN BLSN). If blowing snow is occurring and the observer cannot determine whether or not snow is also falling, then BLSN is reported. Spray (PY) is coded only with blowing (BL).
The descriptor for showery-type precipitation (SH) is coded only with one or more of the precipitation qualifiers for rain (RA), snow (SN), ice pellets (PL), or hail (GR). When any type of precipitation is coded with VC, the intensity and type of precipitation is not coded.
The descriptor for thunderstorm (TS) may be coded by itself when the thunderstorm is without associated precipitation. A thunderstorm may also be coded with the precipitation types of rain (RA), snow (SN), ice pellets (PL), snow pellets (GS), or hail (GR). For example, a thunderstorm with snow and/or GR hail and/or snow pellets would be coded as TSSNGRGS. TS is not coded with SH.
The descriptor freezing (FZ) is only coded in combination with fog (FG), drizzle (DZ), or rain (RA) (e.g., FZRA). FZ is not coded with SH.

Precipitation is any form of water particle, whether liquid or solid, that falls from the atmosphere and reaches the ground. The precipitation types are: drizzle (DZ), rain (RA), snow (SN), snow grains (SG), ice crystals (IC), ice pellets (PL), hail (GR), snow pellets (GS), and unknown precipitation (UP). UP is reported if an automated station detects the occurrence of precipitation, but the precipitation sensor cannot recognize the type.

Obscurations are any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility in the atmosphere. The obscuration types are: mist (BR), fog (FG), smoke (FU), volcanic ash (VC), widespread dust (DU), sand (SA), haze (HZ), and spray (PY). Spray (PY) is coded only as BLPY.
With the exception of volcanic ash, low drifting dust, low drifting sand, low drifting snow, shallow fog, partial fog, and patches (of) fog, an obscuration is coded in the body of the report if the surface visibility is less than
7 miles (mi), or considered operationally significant. Volcanic ash is always reported when observed.

Other weather phenomena types include: well-developed dust/sand whirls (PO), sandstorms (SS), duststorms (DS), squalls (SQ), funnel clouds (FC), and tornados and waterspouts (+FC). Some are noted in this picture.

Sky Condition

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

A description of the sky in ascending order. Includes cloud cover, vertical visibility, or clear skies.
First 3 letters describe the cloud cover followed by the height in 3 digits measured from ground level. This one is Overcast 1000’ AGL Cumulonimbus clouds.

Vertical visibility is a ceiling that is indefinite which is best visualized by this picture


Clear skies are coded with SKC or CLR. SKC indicates an observer sees no clouds. CLR indicates an automated station senses no clouds below 12,000’ AGL.

The ceiling type and reportable height values are determined in this table:

At manual stations cloud layers may be modified by CB (Cumulonimbus) or TCU (Towering Cumulus)

Temp/Dew Point

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

Temp and dew point are coded as 2 digits each with temperature first then dew point reported in celsius. Below zero values are reported with an M first.

Altimeter

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

This ones pretty self explanatory. Measured in inches of mercury to help aircraft indicate height above sea level MSL.

Remarks

METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132

There is a lot of possible remarks. This one indicates the following:
(AO2) indicates automated station with a precipitation discriminator.
TSB25 indicates thunderstorm previously beginning at the 25 minute mark of the hour
TS OHD MOV E- means a thunderstorm is overhead and is moving eastbound.
SLP is sea level pressure , in millibars, this one means sea level pressure is 1,013.2mb.

Here’s a table of possible remarks

Hope you guys find this useful.

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And… bookmarked. Thanks for the info!

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Hate to be that guy.

There are already a few topics about METAR.

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