Height of base:

Between 600 and 6000 m (2000 - 18000 ft) (low to mid-level clouds)

Description:

Very dark, grey ragged shreds; featureless layers

Steady precipitation (rain, snow, graupel)

Ragged base

No visibility of sun

Deep layers, extending over large areas

Occurrence:

World-wide; common in midlatitudes

Made of:

Supercooled water droplets, snow crystals, ice crystals, rain drops

Precipitation:

Moderate, steady precipitation

Formation:

Lowering of altostratus

Droplet growth through coalescence

Ice crystal growth through Bergeron-Wegener process

How to distinguish from …

Altostratus (As)

Ns is darker and produces heavier precipitation

As often allows to determine position of sun

Cumulonimbus (Cb)

Cb produces intermittent very heavy precipitation

Thunder, lightning and hail are signs of Cb

Nimbostratus with pannus

(Hebgen Lake, June 2006)

Nimbostratus

Freiberg, Germany, July07

Nimbostratus

Fichtelberg, Germany, July07

Nimbostratus

Lansing, Michigan, Dec07