When altostratus thickens and becomes rain-bearing, it becomes a nimbostratus cloud.
Height of base: 2,000 - 10,000 ft
Shape: Bands or areas of individual cells
Latin: nimbus - rainy cloud; stratus - flattened or spread out
Precipitation: Continuous rain or snow likely
Nimbostratus clouds are dark, grey, featureless layers of clouds, thick enough to block out the sun. Producing persistent rain, these clouds are often associated with frontal systems provided by mid-latitude cyclones. These are probably the least picturesque of all the main cloud types.
Nimbostratus clouds form through the deepening and thickening of an altostratus cloud, often along warm or occluded fronts. These clouds extend through the lower and mid layers of the troposphere bringing rain to the surface below.
These mid-level clouds are often accompanied by continuous moderate rain or snow and appear to cover most of the sky. Nimbostratus will often bring precipitation which may last for several hours until the associated front passes over.
If there is hail, thunder or lightning present it is a cumulonimbus cloud rather than nimbostratus.
Nimbostratus clouds are featureless, very dense and have little characterisation, so are not classified into 'species' like other cloud types. They are similar to altostratus in this way.
Last updated: 1 August 2016