Cloud & Ceiling Codes
Sky condition is where many pilots misread a METAR — not because the codes are hard, but because the definition of a "ceiling" is specific. This guide covers how cloud coverage is reported, how to read the heights, and the exact rule for finding the ceiling that drives your flight category.
Coverage in eighths (oktas)
Cloud amount is measured in eighths of the sky covered, called oktas, and reported with a three-letter code:
| Code | Coverage | Oktas |
|---|---|---|
SKC / CLR | Sky clear | 0/8 |
FEW | Few | 1/8 – 2/8 |
SCT | Scattered | 3/8 – 4/8 |
BKN | Broken | 5/8 – 7/8 |
OVC | Overcast | 8/8 |
SKC is used by human observers for a clear sky; CLR is used by automated stations when no clouds are detected below 12,000 feet.
Reading the heights
The three digits after the coverage code give the base height in hundreds of feet above ground level (AGL) — not above sea level. BKN080 is a broken layer at 8,000 ft AGL; FEW250 is a few clouds at 25,000 ft AGL. Because the height is AGL, you do not add the field elevation.
AGL, not MSL
BKN030 at an airport 5,000 ft above sea level is 3,000 ft above the airport — about 8,000 ft MSL. For separation from terrain that distinction matters.Vertical visibility (VV)
When the sky is fully obscured — by fog, heavy snow, or smoke — individual layers cannot be seen, so the station reports vertical visibility instead: VV002 means you can see 200 ft straight up before the obscuration blocks the view. VV represents an indefinite ceiling and is treated as a ceiling for flight-category purposes.
How the ceiling is determined
This is the key rule: the ceiling is the height of the lowest layer reported as broken (BKN), overcast (OVC), or as a vertical visibility (VV). Few and scattered layers never count as a ceiling, no matter how low they are, because more than half the sky is still open.
- Scan the layers from lowest to highest.
- Ignore FEW and SCT layers.
- The first BKN, OVC, or VV you reach is the ceiling.
Worked examples
| Sky groups | Ceiling |
|---|---|
FEW025 BKN080 OVC120 | 8,000 ft (first BKN) |
SCT015 SCT040 | No ceiling (only scattered layers) |
OVC004 | 400 ft |
VV002 | 200 ft (indefinite ceiling) |
FEW010 SCT030 BKN050 | 5,000 ft (first BKN) |
In the first row, even though there are clouds at 2,500 ft, they are "few" and do not form a ceiling; the broken layer at 8,000 does. That single distinction can change an airport from IFR to VFR.
CB and TCU suffixes
A layer may carry a suffix: CB for cumulonimbus (thunderstorm cloud) or TCU for towering cumulus. BKN035CB is a broken layer at 3,500 ft made of cumulonimbus — a warning of possible turbulence, lightning, hail, and wind shear.
From ceiling to flight category
Once you have the ceiling, combine it with visibility to get the flight category. Ceiling and visibility are each checked, and the more restrictive of the two decides the category. That process has its own guide: Aviation Flight Categories.
Layers are listed lowest first
A METAR reports up to three cloud layers (more at staffed stations), always from the lowest base to the highest. A layer is only added when its coverage is equal to or greater than the layer below it, so you will not see a scattered layer listed above a broken one. Reading the groups left to right is therefore the same as looking up through the sky from the ground.
Clear-sky codes: SKC, CLR, NSC, NCD
Several codes all mean "no significant cloud", and which one appears tells you how the observation was made:
| Code | Meaning |
|---|---|
SKC | Sky clear — reported by a human observer, no cloud at all |
CLR | Clear below 12,000 ft — automated station detected nothing under that height |
NSC | No significant cloud (used outside the US) |
NCD | No cloud detected by an automated sensor (used outside the US) |
More worked ceiling examples
| Sky groups | Ceiling |
|---|---|
SCT008 BKN015 OVC030 | 1,500 ft (first BKN) |
FEW003 SCT010 | No ceiling (few and scattered only) |
BKN000 | Surface-based ceiling |
SCT025 BKN250 | 25,000 ft |
VV000 | Indefinite ceiling, near-zero vertical visibility |
Ceiling and flight category at a glance
The ceiling alone maps to a flight category as shown below. Remember that visibility is checked the same way and the more restrictive of the two decides the final category, so a high ceiling does not by itself guarantee VFR.
| Ceiling (AGL) | Category from ceiling alone |
|---|---|
| Greater than 3,000 ft | VFR |
| 1,000 to 3,000 ft | MVFR |
| 500 to below 1,000 ft | IFR |
| Below 500 ft | LIFR |
Common mistakes
- Counting a FEW or SCT layer as a ceiling. Only BKN, OVC, and VV form a ceiling.
- Reading heights as MSL. Cloud bases are AGL.
- Ignoring VV. Vertical visibility is an indefinite ceiling and counts.
- Forgetting that automated CLR only means clear below 12,000 ft, not necessarily a cloudless sky.
Limitations
Automated ceilometers sample the sky directly overhead and may miss a broken layer just off to the side, or report a scattered layer that is really broken a mile away. They also cap detection around 12,000 ft. Use the METAR alongside the TAF, pilot reports, and your own eyes.
Always verify officially
Official sources
- FAA Aviation Weather Handbook (FAA-H-8083-28); AC 00-45 — sky-condition and ceiling definitions.
- NWS Aviation Weather Center — aviationweather.gov.