View source for Nimbostratus cloud

{{Short description|Common type of rain cloud}}
{{Infobox cloud type
| name           = Nimbostratus cloud
| image location = Ns1.jpg
| image name     = Nimbostratus with [[scud (cloud)|pannus]]
| abbreviation   = Ns
| symbol         = Clouds CM 2.svg
| genus          = Nimbostratus (''rain, layered'')
| species        = 
| variety        = 
| altitude_m     = 500–5,500
| altitude_ft    = 2,000–18,000
| level          = Medium to low, vertical
| appearance     = Dark and featureless layer cloud full of water vapor; responsible for rain and snow
| precipitation  = Yes: [[rain]], [[ice pellets]], or [[snow]]; sometimes [[virga]]
}}

A '''nimbostratus cloud''' is a multilevel, [[wikt:amorphous|amorphous]], nearly uniform, and often dark-grey [[cloud]] that usually produces continuous [[rain]], [[snow]], or [[rain and snow mixed|sleet]], but no [[lightning]] or [[thunder]].<ref>{{cite encyclopedia |url=http://encyclopedia2.thefreedictionary.com/cloud |title=cloud |encyclopedia=[[Columbia Encyclopedia|Columbia Electronic Encyclopedia]] |publisher=[[Columbia University Press]] |via=[[The Free Dictionary]]}}</ref><ref>{{cite American Heritage Dictionary|nimbostratus}}</ref><ref>{{Cite web |title=nimbostratus {{!}} Definition of nimbostratus in US English by Oxford Dictionaries |url=https://en.oxforddictionaries.com/definition/us/nimbostratus |archive-url=https://web.archive.org/web/20190115182150/https://en.oxforddictionaries.com/definition/us/nimbostratus |archive-date=2019-01-15 |access-date=2025-08-08 |website=Oxford Dictionaries {{!}} English}}</ref>

Although it is usually a low-based stratiform cloud, it actually forms most commonly in the middle level of the troposphere and then spreads vertically into the low and high levels. Nimbostratus usually produces precipitation over a wide area.

The prefix ''[[wikt:nimbo-|nimbo-]]'' comes from the Latin word ''{{Wikt-lang|la|nimbus}}'', which means "rain bearing cloud".

Downward-growing nimbostratus can have the same vertical extent as most large upward-growing [[cumulus]], but its horizontal expanse tends to be even greater.

==Appearance==
Nimbostratus has a diffuse [[cloud base]] generally found near the surface in the lower levels to about {{cvt|2000|to|4000|m|ft}} in the middle levels of the troposphere. Although usually dark at its base, it often appears illuminated from within to a surface observer.<ref name="Nimbostratus">{{cite book |editor=World Meteorological Organization |title=Nimbostratus, International Cloud Atlas |volume=I |year=1975 |url=https://archive.org/details/manualonobservat00worl/page/37 |pages=[https://archive.org/details/manualonobservat00worl/page/37 37–39] |isbn=92-63-10407-7 |access-date=26 August 2014 |url-access=registration }}</ref> Though found worldwide, nimbostratus occurs more commonly in the middle latitudes.<ref name="cloudspotterguide" /> It is coded C<sub>M</sub>2 on the [[SYNOP]] report.

==Formation==
Nimbostratus occurs along a [[warm front]] or [[occluded front]] where the slowly rising warm air mass creates nimbostratus along with shallower stratus clouds producing less rain, these clouds being preceded by higher-level clouds such as [[cirrostratus]] and [[altostratus]].<ref name="dunlop">{{cite book|last=Dunlop|first=Storm|title=Weather Identification Handbook: The Ultimate Guide for Weather Watchers|publisher=Globe Pequot|location=Guilford, Connecticut|year=2003|isbn=1-58574-857-9}}</ref><ref name="earthscience">{{cite book|last=Thompson|first=Graham|author2=Turk, Jonathan |title=Earth Science and the Environment |publisher=Saunders College Publishing|location=Fort Worth|year=1993|isbn=0-03-075446-1}}</ref> Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus.<ref name="lankford">{{cite book|last=Lankford|first=Terry|title=Aviation Weather Handbook|publisher=McGraw-Hill Professional|year=2000|isbn=978-0-07-136103-3|url=https://books.google.com/books?id=kSSn7vPgmUQC&q=nimbostratus+6500}}</ref>

Nimbostratus, unlike cumulonimbus, is not associated with [[thunderstorm]]s, however at an unusually unstable warm front caused as a result of the advancing warm air being hot, humid and unstable, [[cumulonimbus]] clouds may be embedded within the usual nimbostratus. Lightning from an embedded cumulonimbus cloud may interact with the nimbostratus but only in the immediate area around it. In this situation with lightning and rain occurring it would be hard to tell which type of cloud was producing the rain from the ground, however cumulonimbus tend to produce larger droplets and more intense downpours. The simultaneous presence of cumulonimbus and nimbostratus clouds is uncommon; nimbostratus clouds are typically associated with warm fronts and occasionally appear along cold fronts. However nimbostratus in [[Australian east coast low]] pressure systems (ECL) can bring some of the heaviest rainfall totals on record due to the [[Tasman sea]], which is often warm. For instance, Sydney has recorded{{when?|date=September 2025}} a 24-hour rainfall total of {{convert|327.8|mm|in|abbr=on}} purely from nimbostratus, with {{convert|100|mm|in|abbr=on}} falling in the three hours from noon to 3:00{{nbsp}}pm.{{cn|date=September 2025}} The simultaneous presence of cumulonimbus and nimbostratus clouds is common in eastern Australia, and these storms are called "embedded thunderstorms".

==Forecast==
[[File:2023-10-29 12 25 34 View towards dark clouds from Burlington County Route 630 (Woodlane Road) in Westampton Township, Burlington County, New Jersey.jpg|thumb|Nimbostrati often have very few visual features.]]

Nimbostratus is generally a sign of an approaching warm or occluded front producing steady moderate precipitation, as opposed to the shorter period of typically heavier precipitation released by a cold-frontal cumulonimbus cloud.<ref name="cloudspotterguide">{{cite book|last=Pretor-Pinney|first=Gavin|title=The Cloudspotter's Guide: The Science, History, and Culture of Clouds|publisher=Perigee|year=2007|isbn=978-0-399-53345-7|url=https://books.google.com/books?id=MAiKY4xU6y8C}}</ref> Precipitation may last for several days, depending on the speed of the frontal system.<ref name="dunlop" /> A nimbostratus virga cloud is the same as normal nimbostratus, but the rain or snow falls as [[virga]] which doesn't reach the ground. [[Stratus cloud|Stratus]] or [[stratocumulus]] usually replace the nimbostratus after the passage of the warm or occluded front. 

==Origin of name==
{{further|Cloud#History of cloud science and nomenclature}}

Under [[Luke Howard (meteorologist)|Luke Howard]]'s first systematized study of clouds, carried out in France in 1802, three general cloud ''forms'' were established based on appearance and characteristics of formation: ''cirriform'', ''cumuliform'' and ''stratiform''. These were further divided into upper and lower types depending on altitude. In addition to these three main types, Howard added two names to designate multiple cloud types joined together: ''cumulostratus'', a blending of cumulus clouds and stratus layers, and ''nimbus'', a complex blending of cirriform, cumuliform, and stratiform clouds with sufficient vertical development to produce significant precipitation.

Later, in the 20th century, a commission for the study of clouds by the International Meteorological Committee (IMC), a part of the [[International Meteorological Organization]] (IMO), put forward a refined and more restricted definition of the genus nimbus, effectively reclassifying it as a stratiform cloud type. It was then renamed ''nimbostratus'', and published with the new name in the 1932 edition of the ''International Atlas of Clouds and of States of the Sky''. This left cumulonimbus as the only nimboform type as indicated by its root name.

==Subtypes and derivative types==
:*Species and varieties: Nimbostratus is very thick, opaque, and featureless, so this genus type is not subdivided into species or varieties.<ref name="Species">{{cite book |editor=World Meteorological Organization |title=Species, International Cloud Atlas |year=1975 |url=http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf |pages=18–20 |access-date=26 August 2014 |archive-url=https://web.archive.org/web/20160725172359/http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf |archive-date=25 July 2016 |url-status=dead }}</ref><ref name="Varieties">{{cite book |editor=World Meteorological Organization |title=Varieties, International Cloud Atlas |year=1975 |url=http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf |pages=20–22 |access-date=26 August 2014 |archive-url=https://web.archive.org/web/20160725172359/http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf |archive-date=25 July 2016 |url-status=dead }}</ref>
:::*Precipitation-based supplementary features: Nimbostratus is a major precipitation cloud and produces the virga or precipitation features.  The latter can achieve heavy intensity due to the cloud's vertical depth.
:::*Accessory cloud: Nimbostratus pannus is an accessory cloud of nimbostratus that forms as a ragged layer in precipitation below the main cloud deck.<ref name="Features">{{cite book|editor=World Meteorological Organization|editor-link=World Meteorological Organization|title=Features, International Cloud Atlas|volume=I|year=1975|url=https://archive.org/details/manualonobservat00worl/page/22|pages=[https://archive.org/details/manualonobservat00worl/page/22 22–24]|isbn=92-63-10407-7|access-date=26 August 2014|url-access=registration}}</ref> Pannus is coded C<sub>L</sub>7.
:::*Genitus mother clouds: This genus type can form from cumulus and cumulonimbus.
:::*Mutatus mother clouds: Nimbostratus can form due to the complete transformation of altocumulus, altostratus and stratocumulus.

== Relation to other clouds ==
Multi-level nimbostratus is physically related to other stratiform genus-types by way of being non-convective in nature. However, the other sheet-like clouds usually each occupy only one or two levels at the same time. [[Stratus cloud|Stratus]] clouds are low-level and form from near ground level to {{convert|2000|m|ft}} at all latitudes. In the middle level are the [[altostratus]] clouds that form from {{convert|2000|m|ft}} to {{convert|7000|m|ft}} in polar areas, {{convert|7000|m|ft}} in temperate areas, and {{convert|7600|m|ft}} in tropical areas. Although altostratus forms mostly in the middle level of the troposphere, strong frontal lift can push it into the lower part of the high-level. The main high-level stratiform cloud is [[cirrostratus]] which is composed of ice crystals that often produce halo effects around the sun. Cirrostratus forms at altitudes of {{convert|3000|to|7600|m|ft}} in high latitudes, {{convert|5000|to|12000|m|ft}} in temperate latitudes, and {{convert|6100|to|18000|m|ft}} in low, tropical latitudes. <!-- <ref name="nws-jetstream" /> -->  Of the non-stratiform clouds, [[cumulonimbus]] and [[cumulus congestus]] are the most closely related to nimbostratus because of their vertical extent and ability to produce moderate to heavy precipitation.  The remaining cumuliform ([[cumulus]]) and stratocumuliform ([[stratocumulus]], [[altocumulus]], and [[cirrocumulus]]) clouds have the least in common with nimbostratus.

== See also ==

* [[Nimbostratus virga]]
* [[Cumulonimbus cloud|Cumulonimbus]]
* [[List of cloud types]]

==References==
{{Reflist|30em}}

==External links==
{{commons category|Nimbostratus clouds}}
* [https://web.archive.org/web/20060924180030/http://education.arm.gov/nsdl/Library/glossary.shtml#anchorN National Science Digital Library - Nimbostratus]
* [https://web.archive.org/web/20060620003348/http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/atmospheric_moisture/clouds_3.html Nimbostratus and Other Low Clouds]

{{Cloud types}}

[[Category:Cloud types]]
[[Category:Stratus]]