Editing Squall line (section)

===Life cycle===
[[File:Bow echo diagram.svg|thumb|right|Typical evolution of (a) into a bow echo (b, c) and into a comma echo (d).  Dashed line indicates axis of greatest potential for [[downburst]]s.  Arrows indicate wind flow relative to the storm.  Area C is most prone to supporting tornado development.]]

Organized areas of thunderstorm activity reinforce pre-existing frontal zones, and they can outrun cold fronts. This outrunning occurs within the [[westerlies]] in a pattern where the upper-level jet splits into two streams. The resultant [[mesoscale convective system]] (MCS) forms at the point of the upper level split in the wind pattern in the area of best low-level inflow.<ref>{{Cite web |title=Squall Lines, Derechos, and Bow Echoes |url=https://www.e-education.psu.edu/meteo3/l9_p7.html |access-date=2025-03-06 |website=PSU}}</ref><ref>{{Cite web |last=Sharp |first=Nicole |date=2023-07-10 |title=How Squall Lines Form |url=https://fyfluiddynamics.com/2023/07/how-squall-lines-form/ |access-date=2025-03-06 |website=FYFD |language=en-US}}</ref><ref>{{Cite web |title=Thunderstorm Types |url=https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/types/ |access-date=2025-03-06 |website=NOAA National Severe Storms Laboratory |language=EN-US}}</ref>

The convection then moves east and toward the [[equator]] into the warm sector, parallel to low-level thickness lines. When the convection is strong linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise.<ref>{{cite web|author=Office of the Federal Coordinator for Meteorology |year=2008 |url=http://www.ofcm.gov/slso/pdf/slsochp2.pdf |title=Chapter 2: Definitions |pages=2–1 |publisher=[[NOAA]] |access-date=2009-05-03 |url-status=dead |archive-url=https://web.archive.org/web/20090506002006/http://www.ofcm.gov/slso/pdf/slsochp2.pdf |archive-date=2009-05-06 }}</ref>

If squall lines form over arid regions, a dust storm known as a [[haboob]] may result from the high winds in their wake picking up dust from the desert floor.<ref>Western Region Climate Center (2002). [http://www.wrcc.dri.edu/ams/glossary.html#H H.] {{Webarchive|url=https://web.archive.org/web/20170521194533/http://www.wrcc.dri.edu/ams/glossary.html#H |date=2017-05-21 }} Desert Research Institute. Retrieved on 2006-10-22.</ref> Well behind mature squall lines, a wake low can develop on the back edge of the rain shield,<ref>{{cite book|series=Glossary of Meteorology |year=2009 |url=http://glossary.ametsoc.org/wiki/Wake_low |title=Wake Low |archive-url=https://web.archive.org/web/20110606103437/http://amsglossary.allenpress.com/glossary/search?p=1&query=wake+low&submit=Search |archive-date=2011-06-06 |publisher= [[American Meteorological Society]]|isbn=978-1-878220-34-9 |access-date=2019-09-26}}</ref> which can lead to a heat burst due to the warming up of the descending air mass which is no longer being rain-cooled.<ref>{{cite book |series= Glossary of Meteorology |title= Heat burst |publisher= [[American Meteorological Society]] |year= 2009 |url= http://glossary.ametsoc.org/wiki/Heat_burst |isbn= 978-1-878220-34-9 |url-status= live |archive-url= https://web.archive.org/web/20110606102146/http://amsglossary.allenpress.com/glossary/search?id=heat-burst1 |archive-date= 2011-06-06 }}</ref> Smaller [[Cumulus cloud|cumulus]] or [[Stratocumulus cloud|stratocumulus]] clouds, along with [[Cirrus cloud|cirrus]], can be found ahead of the squall line.<ref>{{Cite web |last=Aviation |first=Red Horse |date=2024-06-10 |title=What is a Squall Line? |url=https://www.redhorseaviation.com/post/what-is-a-squall-line |access-date=2025-03-06 |website=Red Horse Aviation |language=en}}</ref>

As [[supercell]]s and [[Multicellular thunderstorm|multi-cell]] thunderstorms dissipate due to a weak shear force or poor lifting mechanisms, (e.g. considerable [[terrain]] or lack of daytime heating) the [[gust front]] associated with them may outrun the squall line itself and the synoptic scale area of low pressure may then infill, leading to a weakening of the cold front; essentially, the thunderstorm has exhausted its updrafts, becoming purely a downdraft dominated system. The areas of dissipating squall line thunderstorms may be regions of low [[Convective available potential energy|CAPE]], low [[humidity]], insufficient wind shear, or poor synoptic dynamics (e.g. an upper-level low filling) leading to [[frontolysis]].