what is meant by the term nimbus regarding clouds
Nimbostratus cloud Nimbostratus is a stratiform genus formerly classified as "Family C" low-level, but now considered by the World Meteorological Organization (WMO) to be a middle- or multi-level stratus type.[1]. Although it is usually a low-based cloud, it actually forms most commonly in the middle level of the troposphere and then spreads vertically into the low and high levels. This change in classification would once have made it a "Family D" cloud, but this style of nomenclature was discontinued by the WMO in 1956. Nimbostratus usually produces precipitation over a wide area. Nimbo- is from the Latin word nimbus, which denotes precipitation. It has a diffuse cloud base generally found anywhere from near surface in the low levels to about 3,000 m (9,800 ft) in the middle level of the troposphere. Although usually dark at its base, it often appears illuminated from within to a surface observer.[2] Nimbostratus usually has a thickness of about 2000 m. Though found worldwide, nimbostratus occurs more commonly in the middle latitudes.[3] It is coded CM2 on the SYNOP report.