Nimbostratus cloud
(重定向自Nimbostratus)
Nimbostratus is a low-to-middle étage stratiform cloud that has considerable vertical and horizontal extent and 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 and about 3,000 m (9,800 ft). This cloud typically forms from altostratus in the middle altitude range, but it tends to thicken into the low altitude range during precipitation. Although usually dark at its base, it often appears illuminated from within to a surface observer. Nimbostratus usually has a thickness of about 2000 m. Though found worldwide, nimbostratus occurs more commonly in the middle latitudes. It is coded CM2 on the SYNOP report.