Editing Thundersnow (section)

==Formation==
Thundersnow is caused by the same mechanisms as regular [[thunderstorm]]s, but it is much more rare because cold dense air is less likely to rise.<ref>{{Cite news |last=Strong |first=Hannah |date=Feb 25, 2022 |title=What is Thundersnow |work=[[WDRB]] |url=https://www.wdrb.com/weather/wdrb-weather-blog/what-is-thundersnow/article_965b3074-8f64-11ec-bb8d-d315410c9e0e.html |access-date=February 27, 2022 |archive-date=February 27, 2022 |archive-url=https://web.archive.org/web/20220227234256/https://www.wdrb.com/weather/wdrb-weather-blog/what-is-thundersnow/article_965b3074-8f64-11ec-bb8d-d315410c9e0e.html |url-status=live }}</ref>

===Lake effect precipitation===
[[Image:October_12-13_radarloop_kbuf.gif|thumb|right|A large squall producing heavy snow and frequent lightning over Buffalo, NY.]]
Lake effect thundersnow occurs after a cold front or [[Shortwave (meteorology)|shortwave]] aloft passes over a body of water. This steepens the thermal [[lapse rate]]s between the lake temperature and the temperatures aloft. A difference in temperature of {{convert|25|C-change}} or more between the lake temperature and the temperature at about {{convert|1500|m|ft|abbr=on}} (the 850 hPa level) usually marks the onset of thundersnow, if surface temperatures are expected to be below freezing. However several factors, including other geographical elements, affect the development of thundersnow.

The primary factor is convective depth. This is the vertical depth in the [[troposphere]] that a parcel of air will rise from the ground before it reaches the equilibrium (EQL) level and stops rising. A minimum depth of {{convert|1500|m|ft|abbr=on}} is necessary, and an average depth of {{convert|3000|m|ft|abbr=on}} or more is generally accepted as sufficient. [[Wind shear]] is also a significant factor. Linear snow squall bands produce more thundersnow than clustered bands; thus a directional wind shear with a change of less than 12° between the ground and {{convert|2000|m|ft|abbr=on}} in height must be in place. However, any change in direction greater than 12° through that layer will tear the snow squall apart. A bare minimum [[Fetch (geography)|fetch]] of {{convert|50|km/h|mph|abbr=on}} is required so that the air passing over the lake or ocean water will become sufficiently saturated with moisture and will acquire thermal energy from the water.

The last component is the echo top or storm top temperature. This must be at least {{convert|-30|C}}. It is generally accepted that at this temperature there is no longer any [[Supercooling|super cooled]] water vapour present in a cloud, but just ice crystals suspended in the air. This allows for the interaction of the ice cloud and graupel pellets within the storm to generate a charge, resulting in lightning and thunder.<ref>the USA Today. Jack Williams. [https://www.usatoday.com/weather/wlakeeff.htm Warm water helps create Great Lakes snowstorms.] {{Webarchive|url=https://web.archive.org/web/20120315102449/http://www.usatoday.com/weather/wlakeeff.htm |date=2012-03-15 }} Retrieved on 01-11-2006.</ref>

===Synoptic forcing===
Synoptic snow storms tend to be large and complex, with many possible factors affecting the development of thundersnow. The best location in a storm to find thundersnow is typically in its [[NorthWest]] [[Quadrant (plane geometry)|quadrant]] (in the [[Northern Hemisphere]], based on observations in the [[Midwestern United States]]), within what is known as the "comma head" of a mature [[extratropical cyclone]].<ref>Patrick S. Market, Angela M. Oravetz, David Gaede, Evan Bookbinder, Rebecca Ebert, and Christopher Melick. [http://ams.confex.com/ams/pdfpapers/72662.pdf Upper Air Constant Pressure Composites of Midwestern Thundersnow Events.] {{Webarchive|url=https://web.archive.org/web/20110609170131/http://ams.confex.com/ams/pdfpapers/72662.pdf |date=2011-06-09 }} Retrieved on 01-11-2006.</ref><ref name="Rauber2014">{{cite journal |title=Stability and Charging Characteristics of the Comma Head region of Continental Winter Cyclones |journal=J. Atmos. Sci. |last=Rauber |first=R.M. |pages=1559–1582 |volume=71 |issue=5 |year=2014 |doi=10.1175/JAS-D-13-0253.1 |bibcode= 2014JAtS...71.1559R|display-authors=etal|doi-access=free }}</ref> Thundersnow can also be located underneath the [[Occluded front|TROWAL]], a trough of warm air aloft which shows up in a [[surface weather analysis]] as an inverted trough extending backward into the cold sector from the main cyclone.<ref>National Weather Service Office, St. Louis, Missouri. [http://www.crh.noaa.gov/lsx/science/pdfppt/thun_prox_soundings.ppt Thundersnow Proximity Soundings.] Retrieved on 01-11-2006. {{webarchive|url=https://web.archive.org/web/20110523213153/http://www.crh.noaa.gov/lsx/science/pdfppt/thun_prox_soundings.ppt |date=2011-05-23 }}</ref> In extreme cases, thunderstorms along the cold front are transported towards the center of the low-pressure system and will have their precipitation change to snow or ice, once the cold front becomes a portion of the occluded front.<ref name="Rauber2014"/> The [[1991 Halloween blizzard]], [[Superstorm of 1993]], and [[White Juan]] are examples of such blizzards featuring thundersnow.

===Upslope flow===
Similar to the lake effect regime, thundersnow is usually witnessed in terrain in the cold sector of an [[extratropical cyclone]] when a shortwave aloft moves into the region. The shortwave will steepen the local lapse rates, allowing for a greater possibility of both heavy snow at elevations where it is near or below freezing, and occasionally thundersnow.<ref>National Weather Service Office, Sacramento, California. Alexander Tardy. [http://www.wrh.noaa.gov/wrh/02TAs/0213/index.html Western Region Technical Attachment No. 02-13: Thundersnow in the Sierra Nevada.] Retrieved on 01-11-2006. {{webarchive|url=https://web.archive.org/web/20061014210656/http://www.wrh.noaa.gov/wrh/02TAs/0213/index.html |date=2006-10-14 }}</ref>