Editing Cirrostratus cloud

{{Short description|Genus of atmospheric cloud}}
{{use dmy dates|date=May 2025}}
{{Infobox cloud type
|name=Cirrostratus cloud
|image location=Cirrostratus with mock sun.jpg
|image name=Cirrostratus nebulosus clouds backlit by the Sun
|abbreviation=Cs
|genus=[[cirrus cloud|Cirrus]] ("curl") and<br>-[[stratus cloud|stratus]] ("layered")
| species= * Fibratus
* Nebulosus
| variety= * Duplicatus
* Undulatus
| level = high
|altitude_m = 6,000–13,000
|altitude_ft = 20,000–43,000
|appearance=Thin, transparent, high-altitude layer capable of producing a halo
|precipitation=No, but usually signal the approach of a warm front that may bring rain within 24 hours
}}

'''Cirrostratus''' ({{IPAc-en|ˌ|s|ɪr|oʊ|ˈ|s|t|r|æ|t|ə|s|,_|-|ˈ|s|t|r|eɪ|t|ə|s}}) is a high-altitude, very thin, and generally uniform [[stratus cloud|stratiform]] genus-type of [[cloud]]. It is composed of [[ice crystal]]s, which are particles of [[ice|frozen water]]. Cirrostratus is difficult to see and can produce [[halo (optical phenomenon)|halos]]. These [[optical phenomenon|optical effects]] are caused when the cloud takes the form of thin [[cirrostratus nebulosus]].<ref name="Cirrostratus">{{cite web |publisher=[[World Meteorological Organization]] |title=Cirrostratus |website=[[International Cloud Atlas]] |volume=I |year=1975 |url=https://archive.org/details/manualonobservat00worl/page/29 |pages=29–31 |isbn=92-63-10407-7 |access-date=2014-07-26}}</ref>

The cloud has a fibrous texture with no halos if it is thicker [[cirrostratus fibratus]]. On the approach of a frontal system, the cirrostratus often begins as nebulous and turns to fibratus. If the cirrostratus begins as fragmented of clouds in the sky it often means the front is weak. Cirrostratus usually lies above {{cvt|5.5|km|mi ft}}. Its presence indicates a large amount of [[moisture]] in the upper [[troposphere]].<ref>{{cite book |last=Ludlum|first=D. |title=National Audubon Society Field Guide to North American Weather |year=1991 |location=New York |publisher=[[Alfred A. Knopf]] |isbn=0-679-40851-7 |page=}}</ref>

Clouds resembling cirrostratus occasionally form in the lower stratosphere over the [[polar regions of Earth]]. [[Polar stratospheric cloud]]s can take on this appearance when composed of tiny [[supercooling|supercooled]] droplets of water or [[nitric acid]].<ref name="PSC">{{cite web |title=Nitric acid and water PSC |year=2017 |url=https://cloudatlas.wmo.int/nitric-acid-and-water-polar-stratospheric-clouds.html |publisher=[[World Meteorological Organization]] |website=[[International Cloud Atlas]] |access-date=2019-04-03}}</ref>

[[File:MoonHaloDonnellyMillsWA 2005 SeanMcClean.jpg|300px|thumb|left|Cirrostratus at night causing a moon halo]]

Cirrostratus clouds sometimes signal the approach of a [[warm front]] if they form after cirrus and spread from one area across the sky, and thus may be signs that [[precipitation]] might follow within the next 12–24&nbsp;hours,<ref>{{cite book |first=Donna|last=Vekteris |year=2004 |title=Scholastic Atlas of Weather |publisher=[[Scholastic Corporation|Scholastic Inc.]] |isbn=0-439-41902-6 |page=14 |url=https://archive.org/details/scholasticatlaso0000unse/page/14}}</ref> or as soon as 6–8&nbsp;hours if the front moves fast. If the cirrostratus is broken fibratus, it can mean that the front is weak and that stratus rather than [[nimbostratus]] will be the precipitating cloud (meaning [[drizzle]] or [[snow grains]] instead of moderate rain or snow).

[[Cumulus humilis]] or [[stratocumulus]] clouds are often found below cirrostratus formations, due to the stable air associated with cirrostratus creating an [[inversion (meteorology)|inversion]] and restricting convection, causing cumuliform clouds to become flattened. [[Contrail]]s also tend to spread out and can be visible for up to an hour in cirrostratus. The phrase "milky sunshine" is often, as well as referring to [[haze]] or light [[mist]], used to refer to the milky appearance of the sky when cirrostratus is present.

[[File:Highcloudsymbols.gif|thumb|300px|High cloud weather map symbols]]

:* Species: Cirrostratus ''fibratus'' (Cs fib) is a high fibrous sheet similar to cirrus but with less detached semi-merged filaments.  It is reported in the SYNOP code as C<sub>H</sub>8 or as C<sub>H</sub>5 or 6 (depending on the amount of sky covered) if increasing in amount.  If the high cloud covers the entire sky and takes on the form of a featureless veil, it is classified as cirrostratus of the species ''nebulosus'' (Cs neb)<ref name="Species">{{cite book|editor=World Meteorological Organization|editor-link=World Meteorological Organization|title=Species, International Cloud Atlas|volume=I|year=1975|url=https://archive.org/details/manualonobservat00worl/page/17|pages=[https://archive.org/details/manualonobservat00worl/page/17 17–20]|isbn=92-63-10407-7|access-date=26 August 2014}}</ref> and is coded C<sub>H</sub>7.
::* Varieties: Cirrostratus species have no opacity-based varieties as they are always translucent. Two pattern-based varieties are sometimes seen with the species fibratus.  These are the closely spaced ''duplicatus'' and wavy ''undulatus'' types similar to those seen with cirrus fibratus.<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>  Pattern-based varieties are not commonly associated with the species nebulosus due to its lack of features.
:::* Supplementary features: Cirrostratus produces no precipitation or virga, and is not accompanied by any accessory clouds.<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}}</ref>
:::* Genitus mother clouds: Cirrostratus fibratus ''cirrocumulogenitus'' sometimes appears as the latter cloud flattens and loses some of its stratocumuliform structure.  Cirrostratus fibratus ''cumulonimbogenitus'' may form if the cirriform top of a mature thundercloud spreads and flattens sufficiently to become a high stratiform cloud.<ref name="wmo-cloud classifications">{{cite web |editor=World Meteorological Organization |title=WMO cloud classifications |year=1995 |url=http://www.weatheranswer.com/public/Clouds_WMO.pdf |access-date=1 February 2012 }}</ref>
:::* Mutatus mother clouds: Cirrostratus fibratus ''cirromutatus'' or ''cirrocumulomutatus'' are the result of a complete transformation from cirrus and cirrocumulus genus types.  Cirrostratus nebulosis ''altostratomutatus'' results when a high grey nebulous altostratus layer thins out into a whitish layer of featureless high cloud.<ref name="wmo-cloud classifications"/>

==See also==
* [[Stratus cloud]]
* [[Altostratus cloud]]
* [[Nimbostratus cloud]]
* [[Cirrostratus nebulosus]]
* [[Altostratus undulatus cloud]]
* [[Fractus cloud]]

==References==
{{Reflist}}

==External links==
{{commons category|Cirrostratus clouds}}
* [http://nephology.eu/cirrostratus International Cloud Atlas – Cirrostratus] {{Webarchive|url=https://web.archive.org/web/20131231042732/http://nephology.eu/cirrostratus |date=2013-12-31 }}

{{Cloud types}}

{{DEFAULTSORT:Cirrostratus Cloud}}
[[Category:Cirrus]]
[[Category:Stratus]]