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rapid within the lower and mid-levels of a mature thunderstorm, updraft and downdraft create distinct mesocenters of pressure. As thunderstorms organized in squall lines, the northern end of the squall line is commonly referred to as the cyclonic end, with the southern side rotating anticyclonically
149:
was referred to as the squall line or cold front. Areas of clouds and rainfall appeared to be focused along this convergence zone. The concept of frontal zones led to the concept of air masses. The nature of the three-dimensional structure of the cyclone was conceptualized after the development of
389:
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
330:
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. This feature is commonly depicted in the warm season across the
705:
winds of 58 miles per hour (93 km/h) during the storm as opposed to gusts, high or rapidly increasing forward speed, and geographic extent (typically 250 nautical miles (500 km; 300 mi) in length.) In addition, they have a distinctive appearance on radar (bow echo); several unique
624:
Another indication of the presence of severe weather along a squall line is its morphing into a line echo wave pattern (LEWP). A LEWP is a special configuration in a line of convective storms that indicates the presence of a low-pressure area and the possibility of damaging winds, large hail, and
596:
is an important aspect of a squall line. In low to medium shear environments, mature thunderstorms will contribute modest amounts of downdrafts, enough to help create a leading edge lifting mechanism – the gust front. In high shear environments created by opposing low level jet winds and synoptic
690:" meaning "straight") is a widespread and long-lived, violent convectively induced straight-line windstorm that is associated with a fast-moving band of severe thunderstorms usually taking the form of a bow echo. Derechos blow in the direction of movement of their associated storms, similar to a
338:
may result from the high winds in their wake picking up dust from the desert floor. Well behind mature squall lines, a wake low can develop on the back edge of the rain shield, which can lead to a heat burst due to the warming up of the descending air mass which is no longer being rain-cooled.
625:
tornadoes. At each kink along the LEWP is a mesoscale low-pressure area, which could contain a tornado. In response to very strong outflow southwest of the mesoscale low, a portion of the line bulges outward forming a bow echo. Behind this bulge lies the mesoscale high-pressure area.
706:
features, such as the rear inflow notch and bookend vortex, and usually manifest two or more downbursts. Although these storms most commonly occur in North
America, derechos occur elsewhere in the world. Outside North America they may be called by different names. For example, in
189:
and the
Eastern U.S (radar coverage is from ground radars, so middle image does not cover the portion over the Gulf). The rightmost image is a couple of hours after the other two, showing the strongest portion of the line as it passes through Florida, Georgia, and South
634:
73:. In the early 20th century, the term was used as a synonym for cold front (which often are accompanied by abrupt and gusty wind shifts). Linear thunderstorm structures often contain heavy
694:, except that the wind is sustained and generally increases in strength behind the "gust" front. A warm weather phenomenon, derechos occur mostly in summer, between May and August in the
405:
From here, a general thinning of a squall line will occur: with winds decaying over time, outflow boundaries weakening updrafts substantially and clouds losing their thickness.
621:. The pressure difference between the mesoscale high and the lower pressures ahead of the squall line cause high winds, which are strongest where the line is most bowed out.
849:
581:, the northern end may evolve further, creating a "comma shaped" wake low, or may continue in a squall-like pattern. The updraft ahead of the line create a
556:
cooled air from downdrafts usually outwardly just above the surface and lifts air into the updrafts unless gushing too far out and cutting off this
158:
315:
Organized areas of thunderstorms activity reinforce pre-existing frontal zones, and they can outrun cold fronts. This outrunning occurs within the
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761:
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Typical evolution of (a) into a bow echo (b, c) and into a comma echo (d). Dashed line indicates axis of greatest potential for
966:"The relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line"
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was concentrated along two lines of convergence, one ahead of the low and another trailing behind the low. The trailing
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617:) within the convective area due to strong descending motion behind the squall line, and could come in the form of a
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323:(MCS) forms at the point of the upper level split in the wind pattern in the area of best low-level inflow.
311:. Arrows indicate wind flow relative to the storm. Area C is most prone to supporting tornado development.
613:
Severe squall lines typically bow out due to the formation of a stronger mesoscale high-pressure system (a
970:
102:
97:. Particularly strong straight-line winds can occur where the linear structure forms into the shape of a
602:
536:
The leading area of a squall line is composed primarily of multiple updrafts, or singular regions of an
459:
239:
710:
and adjacent portions of India, a type of storm known as a "Nor'wester" may be a progressive derecho.
978:
698:. They can occur at any time of the year and occur as frequently at night as in the daylight hours.
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leaves the trailing area of the squall line to the mid-level jet, which aids in downdraft processes.
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347:
398:, insufficient wind shear, or poor synoptic dynamics (e.g. an upper-level low filling) leading to
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thunderstorms dissipate due to a weak shear force or poor lifting mechanisms, (e.g. considerable
363:
359:
86:
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This article is about a line of thunderstorms. For a sudden, sharp increase in wind speed, see
1016:
920:
859:
355:
106:
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winds, updrafts and consequential downdrafts can be much more intense (common in supercell
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as an alternating pattern of two red dots and a dash labelled "SQLN" or "SQUALL LINE".
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186:
134:
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1006:
553:
343:
66:
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The traditional criteria that distinguish a derecho from a severe thunderstorm are
668:
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Cross-section of a squall line showing precipitation, airflow, and surface pressure
351:
1091:
672:
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362:, can be found ahead of the squall line. These clouds are the result of former
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in a pattern where the upper-level jet splits into two streams. The resultant
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United States on surface analyses, as they lie within sharp surface troughs.
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231: in this section. Unsourced material may be challenged and removed.
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too while the downdraft just behind the line will produce a mesohigh.
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335:
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during World War I. This theory proposed that the main inflow into a
28:
17:
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as they move swiftly across a large area. On the back edge of the
36:
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Pressure perturbations around thunderstorms are noteworthy. With
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A squall line over 1,000 mi (1,600 km) long across the
801:
334:
If squall lines form over arid regions, a dust storm known as a
78:
412:
200:
1109:
F. Corfidi; Jeffry S. Evans; Robert H. Johns (Feb 1, 2015).
540:, rising from ground level to the highest extensions of the
992:
10.1175/1520-0493(1988)116<1444:TROSPF>2.0.CO;2
793:
Office of the
Federal Coordinator for Meteorology (2008).
121:
can be present, on very rare occasions associated with a
637:
How a squall line is depicted by the NWS on weather maps
1094:
Merriam-Webster, Incorporated. Retrieved on 2009-05-03.
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137:, derived from a dense network of observation sites in
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winds). Because of the chaotic nature of updrafts and
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clouds having disintegrated, or an area of only minor
1090:
Merriam-Webster's
Spanish/English Dictionary (2009).
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on the leading edge of a derecho as photographed in
34:
Line of thunderstorms along or ahead of a cold front
839:
Desert
Research Institute. Retrieved on 2006-10-22.
49:(MCV) over Pennsylvania with a leading squall line
109:are present. Some bow echoes can grow to become
560:. Visually this process may take the form of a
326:The convection then moves east and toward the
964:Johnson, R. H.; P. J., Hamilton (July 1988).
8:
447:. Unsourced material may be challenged and
101:. Tornadoes can occur along waves within a
990:
577:(in Northern hemisphere). Because of the
511:Learn how and when to remove this message
291:Learn how and when to remove this message
552:, pressure perturbations are important.
150:the upper air network during the 1940s.
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117:associated with mature squall lines, a
1044:
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828:Western Region Climate Center (2002).
564:, often with a turbulent appearance.
7:
445:adding citations to reliable sources
390:thunderstorms may be regions of low
229:adding citations to reliable sources
133:Polar front theory was developed by
69:, often forming along or ahead of a
25:
933:from the original on 2011-06-06.
417:
385:or lack of daytime heating) the
205:
175:
166:
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1013:American Meteorological Society
917:American Meteorological Society
856:American Meteorological Society
760:University of Oklahoma (2004).
370:ahead of the main squall line.
216:needs additional citations for
804:. pp. 2–1. Archived from
59:quasi-linear convective system
1:
1147:Severe weather and convection
762:"The Norwegian Cyclone Model"
641:Squall lines are depicted on
725:Mesoscale convective complex
731:Mesoscale convective vortex
321:mesoscale convective system
47:mesoscale convective vortex
1168:
720:Convective storm detection
661:
26:
1063:Weather Prediction Center
609:Severe weather indicators
1119:National Weather Service
1071:National Weather Service
795:"Chapter 2: Definitions"
643:National Weather Service
105:(LEWP), where mesoscale
1115:Storm Prediction Center
57:, or more accurately a
1008:Line echo wave pattern
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638:
568:Pressure perturbations
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103:line echo wave pattern
50:
1067:"WPC Product Legends"
671:
636:
526:
306:
40:
774:on February 25, 2009
441:improve this section
225:improve this article
983:1988MWRv..116.1444J
696:Northern hemisphere
350:clouds, along with
89:, and occasionally
87:straight-line winds
835:2017-05-21 at the
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354:, and, sometimes,
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107:low-pressure areas
51:
1022:978-1-878220-34-9
926:978-1-878220-34-9
865:978-1-878220-34-9
629:Depiction on maps
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462: –
461:
460:"Squall line"
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456:Find sources:
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426:This section
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240:"Squall line"
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236:Find sources:
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214:This section
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43:weather radar
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1122:. Retrieved
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1076:September 3,
1074:. Retrieved
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1026:. Retrieved
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874:. Retrieved
870:the original
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813:. Retrieved
806:the original
788:
776:. Retrieved
769:the original
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702:
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684:from Spanish
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599:mesocyclones
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439:Please help
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364:cumulonimbus
360:cirrocumulus
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223:Please help
218:verification
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1045:|work=
947:|work=
893:|work=
682:A derecho (
673:Shelf cloud
562:shelf cloud
542:troposphere
400:frontolysis
368:instability
356:altocumulus
139:Scandinavia
95:waterspouts
81:, frequent
55:squall line
45:image of a
1141:Categories
1028:2009-05-03
912:Heat burst
876:2019-09-26
815:2009-05-03
748:References
737:Mesovortex
708:Bangladesh
692:gust front
653:Variations
594:Wind shear
589:Wind shear
550:downdrafts
471:newspapers
387:gust front
379:multi-cell
375:supercells
317:westerlies
309:downbursts
251:newspapers
197:Life cycle
123:heat burst
71:cold front
1047:ignored (
1037:cite book
949:ignored (
939:cite book
895:ignored (
885:cite book
703:sustained
677:Minnesota
619:downburst
428:does not
190:Carolina.
91:tornadoes
85:, strong
83:lightning
1124:March 5,
1092:Derecho.
1015:. 2009.
931:Archived
919:. 2009.
858:. 2009.
851:Wake Low
833:Archived
714:See also
615:mesohigh
574:buoyancy
532:Updrafts
396:humidity
342:Smaller
119:wake low
115:rainband
111:derechos
99:bow echo
1117:of the
979:Bibcode
778:May 21,
688:derecho
664:Derecho
658:Derecho
603:outflow
583:mesolow
538:updraft
485:scholar
449:removed
434:sources
383:terrain
344:cumulus
328:equator
265:scholar
143:cyclone
1019:
923:
862:
742:Squall
645:(NWS)
558:inflow
487:
480:
473:
466:
458:
394:, low
352:cirrus
336:haboob
267:
260:
253:
246:
238:
129:Theory
29:squall
809:(PDF)
798:(PDF)
772:(PDF)
765:(PDF)
733:(MCV)
727:(MCC)
492:JSTOR
478:books
272:JSTOR
258:books
1126:2015
1078:2015
1049:help
1017:ISBN
951:help
921:ISBN
897:help
860:ISBN
802:NOAA
780:2017
464:news
432:any
430:cite
392:CAPE
377:and
244:news
79:hail
63:QLCS
18:QLCS
987:doi
975:116
686:: "
443:by
373:As
358:or
346:or
227:by
93:or
1143::
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61:(
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20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
