METAR remark code

[administrator]

I’ve been looking at a lot of METARs recently and have seen some elements in the RMK section that don’t seem to be described anywhere, e.g.

1CU014
2CU012
3ST013
5CU020

Only one appears in each METAR. The last three digits look like they might denote a height (1400/1200/1300/2000 ft respectively), so it might be some some kind of cloud description (CU=Cumulus/ST=Stratus?).

Is this a standard code and if so, can anyone point me to somewhere that describes it?

[windy2]

could be something like that…
you can actualy put anything you like after a RMK i think, even, “Hi Mom!”

[Vergil83]

I would agree that it must be cloud type, although I have never seen that on a METAR.

What stations are these?

[gajbowles]

These are obsolete cloud descriptors. I forget quite when the change was made but roundabout 10 years ago when the new cloud descriptors (FEW, SCT, BKN and OVC) were introduced followed by a three digit code indicating cloud height in hundreds of feet. The only cloud descriptions now used (TCU - towering cumulus and CB - cumulonimbus) are added after the cloud height. A METAR will have up to three cloud groups.

Thus SCT020 BKN030CB means scattered unclassified clouds at 2000 ft, broken cumulonimbus cloud at 3000 feet.

Chris is right in his understanding of what the obsolete descriptors mean. 6SC008 meant 6 ocktas of stratocumulus cloud at 800 feet.

If my memory is correct, the reason for the change was two fold:

1. There was sometimes differences of opinion as to classification of clouds and
2. For us aviators, the only significant clouds which need to be avoided and not flown through are towering cumulus and cumulonimbus clouds.

For all practical purposes for aviation purposes (which is what a METAR is written for) the present mode of classification works well, and one can make a good educated guess at to what cloud type is to be found from the levels indicated. From a meteorological point of view, the old classification is better because cloud type and a more accurate description of amount of sky covered is given. This type of report is still available as a SYNOP report but the coding for this is less user friendly and the reports themselves not quite so widely available. For European METARS, additional code such as this following RMKS would never be given but it is in quite common use amongst amateur meteorologists posting reports on uk.sci.weather newsgroup and elsewhere.