Editing Altostratus cloud (section)

== Formation ==
[[File:Warm front.svg|thumb|right|upright=2.2|alt=A labeled diagram showing a warm front and the order in which clouds arrive.|Diagram of a warm front]]
Altostratus clouds form when a large [[Air mass|mass of warm air]] rises, causing water vapor in the atmosphere to condense onto nuclei (small dust particles), forming water droplets and ice crystals.<ref name="ucar">{{cite web|url=https://scied.ucar.edu/learning-zone/clouds/how-clouds-form|title=Clouds and How They Form|publisher=University Corporation for Atmospheric Research|access-date=28 March 2022|website=Center for Science Education}}</ref> These conditions usually happen at the leading edge of a warm front, where [[cirrostratus cloud]]s thicken and lower until they transition into altostratus clouds.<ref name="MetOffice" /> Alternatively, nimbostratus clouds can thin into altostratus.<ref name="Cohn-s2355" /> Altostratus can even form from the spreading of the upper [[anvil cloud]] or the middle column of a thunderstorm.<ref name="Cohn-s2355">{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.5.5}}</ref>

Altostratus clouds are mid-level clouds<ref name="Cloud-Classification" /> that form from {{convert|2000|to|4000|m|ft|sigfig=2}} above sea level in [[Polar regions of Earth|polar regions]]. In [[Temperate climate|temperate regions]], the ceiling increases drastically, allowing altostratus clouds to form between {{convert|2000|to|7000|m|ft|sigfig=2}}. In [[Tropical climate|tropical regions]], altostratus can reach even higher, forming from {{convert|2000|to|8000|m|ft|sigfig=2}}.<ref name="WMO-Desc" /> They can range from {{convert|1000|to|5000|m|ft|sigfig=2}} in thickness<ref name="WMO-Desc" /> and can cover hundreds of kilometers of the Earth's surface.<ref>{{harvnb|Cohn|Bruhn|Anderson|Atkinson|2017|loc=Section 2.3.5.7}}</ref>