Nimbostratus
Ns
Nimbostratus
© Wetterkurs.ch
Description
The name Nimbostratus is derived from "nimbus" (Latin: rain cloud) and "stratus" (Latin: spread out, to cover with a layer) and describes a dense, grey cloud layer that completely covers the sky and brings persistent precipitation. Nimbostratus is one of the most distinctive foul-weather clouds and often extends over several kilometres in altitude, with the cloud base typically located in the middle level, while the cloud itself can reach both upward into the high level and downward into the low level. The cloud layer is so thick and opaque that the sun is completely obscured, producing a diffuse, dull light. Below the main cloud deck, ragged cloud fragments known as pannus clouds (Stratus fractus) frequently form, moving rapidly at low altitudes. Nimbostratus often develops through the overrunning of warm air over colder air masses along warm fronts or occluded fronts.
Identification Features
- Uniformly dense, dark grey cloud layer covering the entire sky
- The sun and moon are not visible through the cloud, and no halo is visible
- Persistent, steady precipitation (rain, snow, or freezing rain) reaching the ground
- Cloud base often diffuse and difficult to define
- Frequently accompanied by ragged, low-moving pannus clouds (Stratus fractus) beneath the main layer
- No visible structure or contour at the cloud base
- Great vertical extent, which can span several thousand metres
- Ground-level visibility often severely reduced by precipitation and low cloud cover
Species of this genus
Highlighted: all species that occur with Nimbostratus.
Meteorological Significance
Nimbostratus is the classic persistent rain cloud and signals a pronounced period of bad weather that can last from hours to days. It typically occurs in association with warm fronts, occluded fronts, or extensive low-pressure systems, in which large-scale overrunning of moist air masses takes place. Precipitation from Nimbostratus is steady and prolonged, in contrast to the intense but short-lived showers produced by Cumulonimbus. An improvement in weather can only be expected once the front has passed and the cloud layer begins to break up. Due to the large amounts of precipitation released, Nimbostratus can contribute to flooding and inundation during prolonged frontal weather situations.
Facts
- WMO-Code
- Ns
- Height layer
- Mid-level clouds
- Typical height
- 0.6 - 2.0 km
- Genus
- NIMBOSTRATUS