| Stratus | |
| Abbreviation | Cu |
| Family | C (humilis, mediocris, etc.) or D (congestus, pyrocumulus, etc.) |
| Genus | Cumulus |
| Occurrence | Worldwide |
| Altitude | 600-9000m |
| Formation | weak to moderate convection, sometimes enhanced by atmospheric instability |
| Precipitation | Some varieties can produce showers and storms |
| Potential Hazards | Moderate turbulence at cloud level; may develop into cumulonimbus cumulogenitus |
Cumulus (Cu; Latin for heap) is a common genus of cloud which is formed by the rising of pockets of warm air and which has the appearance of a heap of cloud rising from a horizontal base. The cumulus cloud is commonly described as looking like a cotton ball or as "fluffy". Most of the time, cumulus clouds have a solid white colour, but some "towering" cumulus clouds can become dark. Cumulus congestus clouds can develop into cumulonimbus calvus clouds and thence into cumulonimbus incus clouds; each of these is capable of generating storms and showers.
Cumulus clouds were first described by Luke Howard in 1802 as "convex or conical heaps, increasing upwards from a horizontal base - wool bag clouds".