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.
List of cloud types
In section two of this page (Classification of major types), height ranges are sorted in approximate descending order of altitude expressed in general terms. On the cross-classification table, forms and genus types (including some genus sub-types) are shown from left to right in approximate ascending order of instability.