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.
Cloud
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 and weather maps. The base-height range for each level varies depending on the latitudinal geographical zone. Each altitude level comprises two or three genus types differentiated mainly by physical form.