Cloud types and how to recognize them
The WMO International Cloud Atlas sorts clouds into 10 genera across 3 levels. In temperate regions, the low level runs from the ground to 2 km, the middle level from 2 to 7 km and the high level from 5 to 13 km.
Updated November 7, 2026 · Sources
The three levels
Each level is the range of heights where certain genera occur most often. The levels overlap and their limits change with latitude: in the tropics, the high level reaches 18 km.
| Genera | Polar regions | Temperate regions | Tropical regions |
|---|---|---|---|
| Cirrus, Cirrocumulus, Cirrostratus | 3 – 8 km (10,000 – 25,000 ft) | 5 – 13 km (16,500 – 45,000 ft) | 6 – 18 km (20,000 – 60,000 ft) |
| Altocumulus, Altostratus, Nimbostratus | 2 – 4 km (6,500 – 13,000 ft) | 2 – 7 km (6,500 – 23,000 ft) | 2 – 8 km (6,500 – 25,000 ft) |
| Stratus, Stratocumulus, Cumulus, Cumulonimbus | 0 – 2 km (0 – 6,500 ft) | 0 – 2 km (0 – 6,500 ft) | 0 – 2 km (0 – 6,500 ft) |
High clouds
- Cirrus (Ci): detached clouds of white, delicate filaments, or white or mostly white patches or narrow bands.
- Cirrocumulus (Cc): a thin, white patch, sheet or layer without shading, made of very small elements like grains or ripples.
- Cirrostratus (Cs): a transparent, whitish veil, fibrous or smooth, that often produces a halo around the sun or moon.
Middle clouds
- Altocumulus (Ac): a white or grey patch, sheet or layer, generally with shading, made of laminae, rounded masses or rolls.
- Altostratus (As): a greyish or bluish sheet, striated, fibrous or uniform, thin enough in places to show the sun vaguely, as through ground glass.
- Nimbostratus (Ns): a grey, often dark layer, made diffuse by rain or snow falling more or less continuously.
Low clouds
- Stratocumulus (Sc): a grey or whitish patch, sheet or layer that almost always has dark parts, made of tessellations, rounded masses or rolls.
- Stratus (St): a generally grey layer with a fairly uniform base, which may give drizzle, snow or snow grains.
- Cumulus (Cu): detached, dense clouds with sharp outlines, rising in mounds, domes or towers, often with a cauliflower-like top.
- Cumulonimbus (Cb): a heavy, dense cloud of great vertical extent, shaped like a mountain or huge towers: the thunderstorm cloud.
Clouds that spill over their level
According to the WMO, most clouds stay within their level, with a few exceptions:
- Altostratus is usually in the middle level, but it often extends higher.
- Nimbostratus is almost always in the middle level, but it usually extends into the other two.
- Cumulus and cumulonimbus have their bases in the low level, but their tops may reach the middle and even the high level.
Estimating the height of cumulus
In warm, unstable weather, the cumulus base sits about 227 feet above the ground for each degree Fahrenheit between temperature and dew point, or about 122 meters per degree Celsius, according to the FAA rule. The cloud base tool does the math.