Editing Downburst (section)

==Definition==
[[File:Downburst damage.jpg|thumb|left|Downburst damages in a straight line.]]

A downburst is created by a column of sinking air that after hitting the surface spreads out in all directions and is capable of producing straight-line winds of over {{convert|150|mph|km/h|abbr=on|order=flip}}, often producing damage similar to, but distinguishable from, that caused by tornadoes.<ref name=":0" /> Downburst damage radiates from a central point as the descending column spreads out when hitting the surface, whereas tornado damage tends towards convergent damage consistent with rotating winds. To differentiate between tornado damage and damage from a downburst, the term '''straight-line winds''' is applied to damage from microbursts.

Downbursts in air that is precipitation free or contains [[virga]] are known as '''dry downbursts''';<ref name="micro">Fernando Caracena, Ronald L. Holle, and Charles A. Doswell III. [http://www.cimms.ou.edu/~doswell/microbursts/Handbook.html Microbursts: A Handbook for Visual Identification.] Retrieved on 9 July 2008.</ref> those accompanied with precipitation are known as '''wet downbursts'''. These generally are formed by precipitation-cooled air rushing to the surface, but they perhaps also could be powered by strong winds aloft being deflected toward the surface by dynamical processes in a thunderstorm (see [[rear flank downdraft]]).{{citation needed|date=May 2022}} Most downbursts are less than {{convert|2.5|mi|km|0|abbr=on|order=flip}} in extent: these are called '''microbursts'''.<ref name="Macroburst">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=macroburst&submit=Search Macroburst.] Retrieved on 30 July 2008.</ref> Downbursts larger than {{convert|2.5|mi|km|0|abbr=on|order=flip}} in extent are sometimes called '''macrobursts'''.<ref name="Macroburst"/> Downbursts can occur over large areas. In the extreme case, a series of continuing downbursts results in a [[derecho]], which covers huge areas of more than {{convert|200|mi|km|abbr=on|order=flip}} wide and over {{convert|1000|mi|km|abbr=on|order=flip}} long, persisting for 12 hours or more, and which is associated with some of the most intense straight-line winds.<ref>Peter S. Parke and Norvan J. Larson.[http://www.crh.noaa.gov/dlh/science/event_archive/summer_archive/1999blowdown/1999blowdown.php Boundary Waters Windstorm.] Retrieved on 30 July 2008.</ref>

The term '''microburst''' was defined by [[mesoscale meteorology]] expert [[Ted Fujita]] as affecting an area {{convert|4|km|abbr=on}} in diameter or less, distinguishing them as a type of downburst and apart from common wind shear which can encompass greater areas.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=microburst&submit=Search Microburst.] {{webarchive|url=https://web.archive.org/web/20081212043551/http://amsglossary.allenpress.com/glossary/search?p=1&query=microburst&submit=Search |date=2008-12-12 }} Retrieved on 2008-07-30.</ref> Fujita also coined the term macroburst for downbursts larger than {{convert|4|km|abbr=on}}.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=macroburst&submit=Search Macroburst.] Retrieved on 2008-07-30.</ref>

=== Dry microbursts ===
[[File:Drymicroburst.jpg|thumb|right|250px|Dry microburst schematic]]

When rain falls below the [[cloud base]] or is mixed with dry air, it begins to evaporate and this [[evaporation]] process cools the air. The denser cool air descends and accelerates as it approaches the surface. When the cool air approaches the surface, it spreads out in all directions. High winds spread out in this type of pattern showing little or no curvature are known as straight-line winds.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=straight&submit=Search Straight-line wind.] {{webarchive|url=https://web.archive.org/web/20080415101545/http://amsglossary.allenpress.com/glossary/search?p=1&query=straight&submit=Search |date=2008-04-15 }} Retrieved on 2008-08-01.</ref>

Dry microbursts are typically produced by high based thunderstorms that contain little to no surface rainfall. They occur in environments characterized by a thermodynamic profile exhibiting an inverted-V at thermal and moisture profile, as viewed on a [[Skew-T log-P diagram|Skew-T log-P thermodynamic diagram]]. [[Roger Wakimoto|Wakimoto]] (1985){{Full citation needed|date=April 2025}} developed a conceptual model (over the [[High Plains (United States)|High Plains]] of the United States) of a dry microburst environment that comprised three important variables: mid-level moisture, cloud base in the mid troposphere, and low surface [[relative humidity]]. These conditions evaporate the moisture from the air as it falls, cooling the air and making it fall faster because it is more dense.

=== Wet microbursts ===
[[File:Downburst 1.jpg|thumb|A wet microburst]]

Wet microbursts are downbursts accompanied by significant precipitation at the surface.<ref name="fuj85">* [[Ted Fujita|Fujita, T.T.]] (1985). "The Downburst, microburst and macroburst". SMRP Research Paper 210, 122 pp.</ref> These downbursts rely more on the drag of precipitation for downward acceleration of [[Air parcel|parcels]] as well as the negative [[buoyancy]] which tend to drive "dry" microbursts. As a result, higher [[mixing ratio]]s are necessary for these downbursts to form (hence the name "wet" microbursts). Melting of ice, particularly [[hail]], appears to play an important role in downburst formation (Wakimoto and Bringi, 1988),{{Full citation needed|date=April 2025}} especially in the lowest {{convert|1|km|abbr=on|sigfig=1}} above surface level.<ref>Proctor, 1989</ref>{{Full citation needed|date=April 2025}} These factors, among others, make [[Weather forecasting|forecasting]] wet microbursts difficult.

{| class="wikitable"
|-
! '''Characteristic'''
! '''Dry Microburst'''
! '''Wet Microburst'''
|-
| '''Location of highest probability within the United States'''
| [[Midwestern United States|Midwest]] / [[Western United States|West]]
| [[Southeastern United States|Southeast]]
|-
| '''Precipitation'''
| Little or none
| Moderate or heavy
|-
| '''Cloud bases'''
| As high as 500 hPa (mb)
| As high as 850 hPa (mb)
|-
| '''Features below cloud base'''
| [[Virga]]
| [[Precipitation shaft]]
|-
| '''Primary catalyst'''
| Evaporative cooling
| Precipitation loading and evaporative cooling
|-
| '''Environment below cloud base'''
| Deep dry layer/low relative humidity/dry adiabatic lapse rate
| Shallow dry layer/high relative humidity/moist adiabatic lapse rate
|-
|}

===Straight-line winds=== <!-- the page "Thundergusts" links to this section heading -->
{{see also|Derecho}}
'''Straight-line winds''' (also known as '''plough winds''', '''thundergusts''', and '''hurricanes of the prairie''') are very strong winds that can produce damage, demonstrating a lack of the rotational damage pattern associated with tornadoes.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=straight&submit=Search Straight-line wind.] {{webarchive|url=https://web.archive.org/web/20080415101545/http://amsglossary.allenpress.com/glossary/search?p=1&query=straight&submit=Search |date=15 April 2008 }} Retrieved on 1 August 2008.</ref> Straight-line winds are common with the [[gust front]] of a thunderstorm or originate with a downburst from a thunderstorm. These events can cause considerable damage, even in the absence of a tornado. The winds can gust to {{convert|130|mph|m/s|abbr=on|order=flip}}<ref>{{Cite web|url=https://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm|title=Facts About Derechos - Very Damaging Windstorms|website=www.spc.noaa.gov}}</ref> and winds of {{convert|58|mph|m/s|abbr=on|order=flip}} or more can last for more than twenty minutes.<ref>{{Cite web|url=http://www.spc.noaa.gov/misc/AbtDerechos/casepages/jun291998page.htm|title = The Corn Belt Derecho of 29 June 1998}}</ref> In the United States, such straight-line wind events are most common during the spring when instability is highest and weather fronts routinely cross the country.{{citation needed|date=July 2017}} Straight-line wind events in the form of derechos can take place throughout the eastern half of the U.S.<ref>{{Cite web|url=https://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm#climatology|title=Facts About Derechos - Very Damaging Windstorms|website=www.spc.noaa.gov}}</ref>

Straight-line winds may be damaging to marine interests. Small ships, cutters and sailboats are at risk from this meteorological phenomenon.{{citation needed|date=July 2017}}