Editing Freezing rain (section)

== Mechanism ==
[[File:Ice Storm Chart.svg|thumb|left|upright=0.75|Temperature versus height diagram for different types of [[precipitation]]. The red line shows how freezing rain forms, from [[snow]] through the warm layer and then into the "[[supercooled]] stage".]]
<!--[[File:Freezing Rain skew-t.gif|thumb|[[Skew-T]] sounding taken during a freezing rain event. Temperatures aloft are well above freezing and cool significantly closer to the ground, allowing precipitation to fall as rain and freeze upon reaching the ground.]]-->
Freezing rain is often associated with the approach of a [[warm front]], when subfreezing air (temperatures at or below freezing) is trapped in the lowest levels of the atmosphere while warm air is [[Advection|advected]] aloft.<ref name=U-Ill>{{cite web|publisher=University of Illinois |date=1999-10-04 |title=Cyclones and Fronts: the development of freezing rain |work=WW2010: The Weather World 2010 Project |access-date=2022-02-21 |url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/zr/cond/cyc.rxml}}</ref> This happens, for instance, when a low pressure system moves from the [[Mississippi River]] Valley toward the [[Appalachian Mountains]] and the [[Saint Lawrence River]] Valley of [[North America]] during the cold season, with a strong high pressure system sitting further east. This setup is known as [[cold-air damming]], and is characterized by very cold and dry air at the surface within the region of high pressure. The warm air from the [[Gulf of Mexico]] is often the fuel for freezing precipitation.<ref name=DP>{{cite web |url=http://www.msc-smc.ec.gc.ca/media/icestorm98/icestorm98_a_closer_look_e.cfm |author=[[David Phillips (climatologist)|David Phillips]] |title=Ice Storm of 1998 |date=2002-12-18 |access-date=2022-02-21 |archive-url=https://web.archive.org/web/20060626235616/http://www.msc-smc.ec.gc.ca/media/icestorm98/icestorm98_a_closer_look_e.cfm |archive-date=26 June 2006 |url-status=dead}}</ref>

Freezing rain develops when falling snow encounters a layer of warm air aloft, typically around the {{convert|800|mbar|hPa kPa|abbr=on|lk=on}} level, causing the snow to melt and become rain. As the rain continues to fall, it passes through a layer of subfreezing air just above the surface and cools to a temperature below freezing ({{convert|0|C|F K|disp=or}}). If this layer of subfreezing air is sufficiently deep, the raindrops may have time to freeze into [[ice pellets]] (sleet) before reaching the ground. However, if the subfreezing layer of air at the surface is very shallow, the rain drops falling through it will not have time to freeze and they will hit the ground as [[Supercooling|supercooled]] rain. When these supercooled drops make contact with the ground, power lines, tree branches, aircraft, or anything else below 0 °C, a portion of the drops instantly freezes, forming a thin film of ice, hence freezing rain.<ref>{{cite web|publisher=University of Illinois |date=1999-10-04 |title=Cyclones and Fronts: the definition of freezing rain. |work=WW2010: The Weather World 2010 Project |url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/zr/frz.rxml|access-date=2022-02-21}}</ref><ref>{{cite web |url=http://www.theweatherprediction.com/habyhints/210/ |title=The Rate at which Rain Freezes in a Freezing Rain Event |access-date=2022-02-21 |author=Jeff Haby |date=2014-02-15 }}</ref>  The specific physical process by which this occurs is called [[Nucleation#Examples|nucleation]].<ref>{{cite web|url=https://glossary.ametsoc.org/wiki/Nucleation|title=Nucleation |work=Glossary of Meteorology |publisher=[[American Meteorological Society]]|access-date=2022-02-21}}</ref>
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