Nimbostratus cloud
Under Luke Howard's first systematized study of clouds, carried out in France in 1802, three general cloud "forms" were established based on appearance and characteristics of formation: "cirriform," "cumiliform" and "stratiform." These were further divided into upper and lower types depending on altitude. In addition to these three main types, Howard added two names to designate multiple cloud types joined together: "cumulostratus," a blending of cumulus clouds and stratus layers, and "nimbus," a complex blending of cirriform, cumuliform, and stratiform clouds with sufficient vertical development to produce significant precipitation.
Cumulus congestus cloud
Cumulus congestus clouds are characteristic of unstable areas of the atmosphere which are undergoing convection. They are often characterized by sharp outlines and great vertical development. Because they are produced by strong updrafts, they are typically taller than they are wide, and cloud tops can reach , or higher in the tropics. Cumulus congestus clouds are formed by the development of cumulus mediocris generally, though they can also be formed from altocumulus castellanus or stratocumulus castellanus as well. The "congestus" species of cloud can only be found in the genus "cumulus" and is designated as "towering cumulus" (Tcu) by the International Civil Aviation Organization. Congestus clouds are capable of producing severe turbulence and showers of moderate to heavy intensity. This species is classified as vertical or multi-étage and is coded C2 in the synop report. These clouds are usually too large and opaque to have any opacity or pattern-based varieties.