Editing Altostratus cloud (section)

== Relation to other clouds ==
{{See also|List of cloud types}}
[[File:Cloud types en.svg|thumb|left|upright=1.6|alt=A diagram showing clouds at various heights|Heights of various cloud genera including high-, mid-, and low-level clouds]]
Altostratus and [[altocumulus cloud]]s are the two genera of mid-level clouds that usually form between {{convert|6500|and|20000|ft|m|order=flip|abbr=on}}.<ref name="Cloud-Classification" /><ref name="wmo-cloud-classification" /> These are given the prefix "alto-". These clouds are formed from ice crystals, supercooled water droplets, or liquid water droplets.<ref name="Cloud-Classification" />

Above the mid-level clouds are three different genera of high-level clouds, [[Cirrus cloud|cirrus]], [[cirrocumulus]], and cirrostratus, all of which are given the prefix "cirro-". High-level clouds usually form above {{convert|20000|ft|m|order=flip|abbr=on}}.<ref name="Cloud-Classification" /><ref name="wmo-cloud-classification">{{cite web|url=https://public-old.wmo.int/en/WorldMetDay2017/classifying-clouds|archive-url=https://web.archive.org/web/20231218182558/https://public-old.wmo.int/en/WorldMetDay2017/classifying-clouds|url-status=dead|archive-date=December 18, 2023|accessdate=14 March 2022|title=Classifying clouds| date=18 January 2017 |publisher=[[World Meteorological Organization]]}}</ref><ref name="H&H-340">{{harvnb|Hubbard|2000|p=340}}</ref> Cirrocumulus and cirrostratus are sometimes informally referred to as ''cirriform clouds'' because of their frequent association with cirrus.<ref>{{cite web|url=https://glossary.ametsoc.org/wiki/Cirriform|title=Cirriform – Glossary of Meteorology|access-date=23 February 2022|publisher=American Meteorological Society}}</ref>

Below the mid-level clouds are the low-level clouds, which usually form below {{convert|6500|ft|m|order=flip|abbr=on}} and do not have a prefix.<ref name="Cloud-Classification" /><ref name="wmo-cloud-classification" /> The two genera that are strictly low-level are [[stratus cloud|stratus]], and [[stratocumulus cloud|stratocumulus]]. These clouds are composed of water droplets, except during winter when they are formed of [[supercooled water]] droplets or ice crystals if the temperature at cloud level is below freezing. Three additional genera usually form in the low altitude range, but may be based at higher levels under conditions of very low humidity. They are the genera [[cumulus cloud|cumulus]], and [[cumulonimbus cloud|cumulonimbus]], and [[Nimbostratus cloud|nimbostratus]]. These are sometimes classified separately as clouds of vertical development, especially when their tops are high enough to be composed of supercooled water droplets or ice crystals.<ref name="Plymouth State Meteorology">{{cite web | url=http://vortex.plymouth.edu/clouds.html/ | title=Plymouth State Meteorology Program Cloud Boutique | author=Koermer, Jim | year=2011 | access-date=2 April 2012 | publisher=[[Plymouth State University]] | archive-date=10 May 2009 | archive-url=https://web.archive.org/web/20090510231716/http://vortex.plymouth.edu/clouds.html/ | url-status=dead }}</ref><ref name="Cloud-Classification" />

=== Cirrostratus ===
{{Main|Cirrostratus cloud}}
[[File:Close Cirrostratus.jpg|thumb|alt=Milky-white cirrostratus clouds cause the sky to appear lighter and have a milky tint.|Cirrostratus cloud]]

Cirrostratus clouds can appear as a smooth veil in the sky<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.3.1}}</ref> or as a striated sheet.<ref name="H&H-340"/> They are sometimes similar to altostratus and are distinguishable from the latter because the sun or moon is always clearly visible through transparent cirrostratus, in contrast to altostratus which tends to be opaque or translucent.<ref name="Day-56">{{harvnb|Day|2005|p=56}}</ref> Cirrostratus come in two species, ''fibratus'' and ''nebulosus''.<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.3.2}}</ref> The ice crystals in these clouds vary depending upon the height in the cloud. Towards the bottom, at temperatures of around {{convert|-35|to|-45|C|F}}, the crystals tend to be long, solid, hexagonal columns. Towards the top of the cloud, at temperatures of around {{convert|-47|to|-52|C|F}}, the predominant crystal types are thick, hexagonal plates and short, solid, hexagonal columns.<ref name="parungo-254">{{harvnb|Parungo|1995|p=254}}</ref><ref name="parungo-256">{{harvnb|Parungo|1995|p=256}}</ref> These clouds commonly produce halos, and sometimes the halo is the only indication that such clouds are present.<ref name="ahrens-120">{{harvnb|Ahrens|2006|p=120}}</ref> They are formed by warm, moist air being lifted slowly to a very high altitude.<ref>{{harvnb|Hamilton|2007|p=24}}</ref> When a warm front approaches, cirrostratus clouds become thicker and descend forming altostratus clouds,<ref name="Cloud-Classification"/> and rain usually begins 12 to 24 hours later.<ref name="ahrens-120"/>

=== Altocumulus ===
{{Main|Altocumulus cloud}}
[[File:Altocumulus cloud.jpg|thumb|alt=Small shreds of white altocumulus clouds against a blue sky.|Altocumulus clouds]]
Altocumulus clouds are small patches or heaps of white or light gray cloud.<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.4.1}}</ref><ref name="Cloud-Classification" /> Like altostratus, altocumulus are composed of a mixture of water droplets, supercooled water droplets, and ice crystals. Although altocumulus clouds are mid-level clouds that form at roughly the same altitude as altostratus clouds, their formation methods are completely different. Altocumulus forms from [[convection|convective]] (rising) processes,<ref name="Cloud-Classification" /> whereas altostratus is usually formed by descending and thickening cirrostratus.<ref name="MetOffice" />

=== Stratus ===
{{Main|Stratus cloud}}
[[File:2020-05-18 09 13 58 Stratus clouds with bases that are about 700 feet above ground level over the KLWX WSR-88D NEXRAD in the Dulles section of Sterling, Loudoun County, Virginia.jpg|thumb|alt=A featureless gray stratus cloud.|Stratus cloud]]
Stratus are low-level clouds that are usually visually similar to altostratus.<ref name="Cloud-Classification" /> Stratus comes in two species: ''nebulosus'', a largely-featureless flat gray cloud sheet, and ''fractus'', shattered fragments of cloud<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.8.2}}</ref> often called "scud".<ref name="Cloud-Classification" /> Opaque varieties of altostratus and ''stratus nebulosus'' clouds can be virtually indistinguishable from each other to the naked eye, to the point that the [[World Meteorological Organization]] suggests that one of the few ways to distinguish between these clouds is to check what types of clouds came before them.<ref name="Cohn-s23566">{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.5.6.6}}</ref> Altostratus clouds, because they tend to form from warm fronts,<ref name="MetOffice" /> are usually preceded by high-level cirriform clouds.<ref name="Cohn-s23566" /> Stratus clouds tend to form by cooling air masses, often at night,<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.8.8}}</ref> and thus are not usually preceded by other types of clouds.<ref name="Cohn-s23566" />

=== Nimbostratus ===
{{Main|Nimbostratus cloud}}
Nimbostratus are low-level (sometimes classified as vertical) rain-bearing stratus clouds. Unlike the sprinkles or light drizzles that altostratus or stratus can produce, nimbostratus produces heavy, continuous rain or snow. These clouds are thick and dark enough to entirely blot out the sun.<ref name="Cloud-Classification" /><ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.6.1}}</ref> Nimbostratus has no species<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.6.2}}</ref> or varieties.<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.6.3}}</ref> Like altostratus, nimbostratus clouds can be made of ice crystals, supercooled water droplets, or water droplets.<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.6.7}}</ref>
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