Appears in METARs and TAFs
Cloud cover: FEW, SCT, BKN, OVC
How much of the sky is covered, measured in eighths, and how high the base sits.
FEWSCTBKNOVCNSCNCDCloud amount is reported in eighths of the sky, called oktas. FEW is 1 to 2 oktas, SCT (scattered) is 3 to 4, BKN (broken) is 5 to 7, and OVC (overcast) is 8 — completely covered. Each layer gets its own group, listed from the lowest base upwards.
The three digits after the code give the base height in hundreds of feet above aerodrome elevation, not above sea level. BKN014 is a broken layer with its base at 1 400 ft above the field. A cloud type may follow where it matters: CB for cumulonimbus and TCU for towering cumulus are the two that must be reported, because both indicate convective hazard.
The ceiling is the height of the lowest BKN or OVC layer — the lowest layer covering more than half the sky. FEW and SCT layers do not constitute a ceiling however low they are, which is why an aerodrome can report cloud at 200 ft and still have no ceiling. Three codes replace the groups entirely: NSC for no significant cloud, NCD for no cloud detected by an automatic station, and SKC for a genuinely clear sky.
In a real report
METAR KJFK 311651Z 18017G27KT 10SM FEW015 BKN110 OVC250 22/17 A2996
Three layers, lowest first: few at 1 500 ft, broken at 11 000 ft, overcast at 25 000 ft. The ceiling is 11 000 ft — the lowest broken layer, not the few at 1 500 ft.