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Yesterday, this metar was published:

METAR UUEE 292000Z 07003MPS CAVOK 17/12 Q1013 R06L/CLRD62 R06R/CLRD62 NOSIG=

Can someone explain the meaning of the R06L/CLRD62 R06R/CLRD62 bit? I suspect it means the runway has been cleared but I'm not sure about the details.

More generally, is there a definitive METAR specification that cover these edge cases?

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The World Meteorological Organisation writes the code on behalf of ICAO.

The standard can be found here

You want to have a look at section 15.13.6.

So according to WMO code, R06L/CLRD62 indicates that the contamination on runway 06 Left (parallel) has ceased to exist and surface friction is 0.62 (cf table 0366)

Note that the FAA deviates from this standard, their standard can be found here

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The format follows a standard, although this one is different because of the R at the front...

The format is the "Runway State Group":

First two digits are the Runway Number, 88 means all runways, 99 means a "repetition of the last message as no new information received".

The third digit is the runway deposits, it tells you what is on the runway:

0 = Clear and dry
1 = Damp
2 = Wet or water patches
3 = Rime or frost covered (depth normally less than 1mm)
4 = Dry snow
5 = Wet snow
6 = Slush
7 = Ice
8 = compacted or rolled snow
9 = frozen ruts or ridges
/ = type of deposit not reported (e.g. due to rwy clearance in progress)

The Fourth digit is the extent of the contamination:

1 = 10% or less
2 = 11% to 25%
5 = 26% to 50%
9 = 51% to 100%
/ = not reported (e.g. due to rwy clearance in progress)

The fifth and sixth digits are the depth of deposit:

00 = less than 1mm
01 = 1mm etc

to

90 = 90mm
91 = not used
92 = 10cm
93 = 15cm
94 = 20cm
95 = 25cm
96 = 30cm
97 = 35cm
98 = 40cm or more
99 = Rwy(s) non-operational due to snow, slush, ice, large drifts or runway clearance, but depth not reported.
// = depth of deposit operationally not significant or measurable.

And the seventh and eighth digits are the braking action:

28 = friction coefficient 0.28
38 = friction coefficient 0.38

or

91 = Braking action: Poor
92 = Braking action: Medium/Poor
93 = Braking action: Medium
94 = Braking action: Medium/Good
95 = Braking action: Good
99 = Figures unreliable (e.g. if equipment has been used which does not measure satisfactorily in slush or snow.)
// = Braking action not reported (e.g. runway not operational; aerodrome closed; etc.)

So we can take your example: R06L/CLRD62

Means

R06L : Runway 06 Left
/ : Deposit not reported (clearance in progress)
CLRD: Contamination ceases to exist, so two groups omitted
62: Friction coefficient 0.62

Source: Skybrary.aero But I can't find one definitive source with all the possible reporting in a METAR, sadly.

It seems that this "Runway State Group" is mostly used in European countries, I can't find an example of it used in the U.S.. Here is one good reference which I think covers 99% of the METAR data for Europe.

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    $\begingroup$ Should be in Annex 3 of the Chicago Convention and also "Proposals for the amendment of Annexes [...] and PANS-ATM relating to the use of an enhanced global reporting format for assessing and reporting runway surface conditions" (source: ICAO). $\endgroup$ – mins Jul 1 '17 at 20:00
  • $\begingroup$ @mins thanks for the reference, you are spot on - the format in that document matches the METAR I found. The format in this answer may be outdated. $\endgroup$ – assylias Jul 2 '17 at 15:00

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