Definition - What does Nimbostratus mean?
Nimbostratus are the low to middle level laminated clouds which produce light to moderate precipitation over a large area. They consist of water droplets because their bases lie 2,000 meters or 6,500 feet below them. The clouds contain snow and ice particles instead of water droplets when the temperatures are cold. They can be found worldwide but they commonly occur in the middle latitudes. On the mountain sides, these clouds can be seen descending or ascending the slopes as the rainstorm departs or arrives.
Petropedia explains Nimbostratus
Nimbostratus arises along an occluded or warm front where the gently rising warm air mass forms nimbostratus together with shallower stratus clouds which produce less rain. These clouds are foreshadowed by other clouds of higher level like altostratus and cirrostratus. When the altostratus clouds descend and thicken into lower altitudes, they become nimbostratus. They can be distinguished easily from the mid level altostratus clouds as the moon or the sun is not visible through them. These clouds can contain water droplets, snowflakes or ice particles. Their composition varies based on the temperature and can be mixed with the super-cooled droplets of water and ice particles which are present on the same layer. When these clouds are accompanied by lightning, hail or thunder they are referred to as cumulonimbus.