Cumuliform

Cumuliform
Cumuliform clouds generally appear in isolated heaps or tufts.[36][37] They are the product of localized but generally free-convective lift where no inversion layers are in the troposphere to limit vertical growth. In general, small cumuliform clouds tend to indicate comparatively weak instability. Larger cumuliform types are a sign of greater atmospheric instability and convective activity.[38] Depending on their vertical size, clouds of the cumulus genus type may be low-level or multi-level with moderate to towering vertical extent.[4]

Cumulonimbiform

Cumulonimbus cloud over the Gulf of Mexico in Galveston, Texas
See also: Atmospheric convection
The largest free-convective clouds comprise the genus cumulonimbus, which have towering vertical extent. They occur in highly unstable air[14] and often have fuzzy outlines at the upper parts of the clouds that sometimes include anvil tops.[5] These clouds are the product of very strong convection that can penetrate the lower stratosphere.

Levels and genera
See also: Weather map and Station model
Tropospheric clouds form in any of three levels (formerly called étages) based on altitude range above the Earth’s surface. The grouping of clouds into levels is commonly done for the purposes of cloud atlases, surface weather observations,[4] and weather maps.[39] The base-height range for each level varies depending on the latitudinal geographical zone.[4] Each altitude level comprises two or three genus-types differentiated mainly by physical form.[40][5]

The standard levels and genus-types are summarised below in ap