Mesoscale convective systems

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Mesoscale convective Mesoscale convective systems systems

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Mesoscale convective systems. Review of last lecture. 3 stages of supercell tornado formation. Tornado outbreak (number>6) Tornado damage: Enhanced Fujita Scale (EF-0 65-85 mph, EF-5 >200 mph) - PowerPoint PPT Presentation

Transcript of Mesoscale convective systems

Page 1: Mesoscale convective systems

Mesoscale convective systemsMesoscale convective systems

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Review of last lectureReview of last lecture

1.1. 3 stages of supercell tornado formation. 3 stages of supercell tornado formation.

1.1. Tornado outbreak (number>6) Tornado outbreak (number>6)

2.2. Tornado damage: Enhanced Fujita Scale (EF-0 65-85 Tornado damage: Enhanced Fujita Scale (EF-0 65-85 mph, EF-5 >200 mph)mph, EF-5 >200 mph)

3.3. Tornado occurrence: Global and U.S.. Which country Tornado occurrence: Global and U.S.. Which country has the largest number of tornadoes in the world? has the largest number of tornadoes in the world? Which state has the largest number of tornadoes per Which state has the largest number of tornadoes per unit area in U.S.? Tornado season in U.S. (March-unit area in U.S.? Tornado season in U.S. (March-July)July)

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Convective systemsConvective systems

TornadoesTornadoes: about : about 100-600 m100-600 m, last , last 1 minute to 1 hour1 minute to 1 hour

ThunderstormsThunderstorms: about : about 10 Km10 Km, last , last 10 minutes to a 10 minutes to a couple of hours. couple of hours. 3 types: ordinary, multicell, supercell3 types: ordinary, multicell, supercell

Mesoscale convective systems (MCSs)Mesoscale convective systems (MCSs): A cloud : A cloud system that occurs in connection with an ensemble system that occurs in connection with an ensemble of thunderstorms and produces a contiguous of thunderstorms and produces a contiguous precipitation area on the order of precipitation area on the order of 100 Km100 Km or more in or more in at least one directionat least one direction, and often last for , and often last for several hours several hours to a couple of daysto a couple of days..

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1. Mesoscale Convective Complex1. Mesoscale Convective Complex

2. Squall line

2 types of Mesoscale Convective Systems 2 types of Mesoscale Convective Systems

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Video: Mesoscale convective complexVideo: Mesoscale convective complex

https://www.youtube.com/watch?v=3y7mxqNXYpc https://www.youtube.com/watch?v=3y7mxqNXYpc

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An organized mass, or collection, of An organized mass, or collection, of thunderstorms that extends across a thunderstorms that extends across a large region is called a large region is called a mesoscale mesoscale convective complex (MCC).convective complex (MCC). They can They can be up to 1000 x larger than individual be up to 1000 x larger than individual storms.storms.

With weak upper level winds, such With weak upper level winds, such MCC's can regenerate new storms and MCC's can regenerate new storms and last for upwards of 12 hours and may last for upwards of 12 hours and may bring hail, tornadoes, and flash floods.bring hail, tornadoes, and flash floods.

They often form in summer beneath a They often form in summer beneath a ridge of high pressure, with moisture ridge of high pressure, with moisture fed from S by low level jets.fed from S by low level jets.

Mesoscale Convective Systems Mesoscale Convective Systems I. Mesoscale Convective Complex (MCC)I. Mesoscale Convective Complex (MCC)

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Formation of MCCFormation of MCC

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Global distribution of MCCsGlobal distribution of MCCs

From Doswell et al. 2000

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• A squall line may A squall line may contain several severe contain several severe thunderstorms, some thunderstorms, some possibly supercells, possibly supercells, extending for more extending for more than 1000 kilometers.than 1000 kilometers.

• A squall line always A squall line always contains a convective contains a convective precipitation region precipitation region and a trailing stratiform and a trailing stratiform precipitation region.precipitation region.

Mesoscale Convective SystemsMesoscale Convective SystemsII. Squall LineII. Squall Line

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Vertical structure of squall linesVertical structure of squall lines

Zipser (1977), modified by Houze (1993)

Convective updrafts (controlled by lower troposphere temperature and moisture)

Mesoscale updrafts

Convective downdrafts

Mesoscale downdrafts

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Development of a squall lineDevelopment of a squall line

Thunderstorm stageThunderstorm stage

Bow echo stageBow echo stage

Comma or line echo stageComma or line echo stage

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Developement of a squall line:Developement of a squall line:Horizontal viewHorizontal view

1. Thunderstorm 2. Bow echo 3. Comma echo

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Video: The June 2012 DerechoVideo: The June 2012 Derecho

http://www.youtube.com/watch?http://www.youtube.com/watch?v=K61qGvKltL8 v=K61qGvKltL8

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DerechosDerechos• A derecho (spanish word meaning “straight ahead”) is a widespread,

long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms (often a squall line).

• By definition, the wind damage swath extends more than 240 miles and wind speed > 57 mph. Can produce destruction similar to that of tornadoes. The damage typically is directed in one direction along a relatively straight swath.

From NOAA SPC Derecho website

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Clouds associated with a derechoClouds associated with a derecho

From NOAA SPC Derecho website

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"The Line Storm," by John Steuart "The Line Storm," by John Steuart Curry, 1897-1946Curry, 1897-1946

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Different types of derechosDifferent types of derechos

Serial derechosSerial derechos Progressive derechosProgressive derechos Hybrid derechosHybrid derechos Low dewpoint derechosLow dewpoint derechos

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Serial derechoSerial derecho typically is associated with an typically is associated with an

extensive extensive squall line or squall line or quasi-linear convective quasi-linear convective systemsystem with multiple with multiple embedded bow echoes. embedded bow echoes.

usually occur in conjunction usually occur in conjunction with well-defined, migratory with well-defined, migratory low pressure system. low pressure system.

Overall convective system Overall convective system (and, therefore, derecho) (and, therefore, derecho) motion is dominated by motion is dominated by advectionadvection --- the downstream --- the downstream movement of individual movement of individual thunderstorm cells by the thunderstorm cells by the environmental wind. environmental wind.

From NOAA SPC Derecho website

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Progressive derechoProgressive derecho

typically is associated with a typically is associated with a squall line of restricted length squall line of restricted length that may involve a single that may involve a single bow echo or multiple bows. bow echo or multiple bows.

usually are associated with a usually are associated with a stagnant large scale weather stagnant large scale weather pattern. pattern.

Overall convective system Overall convective system (and, therefore, derecho) (and, therefore, derecho) motion is dominated by motion is dominated by thunderstorm thunderstorm propagationpropagation --- that is, the development of --- that is, the development of new storm cells downstream new storm cells downstream from existing ones. from existing ones.

June 2012 derecho over the Midwest and Ohio Valley

From NOAA SPC Derecho website

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Annual number of derecho eventsAnnual number of derecho events

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Timing of derecho eventsTiming of derecho events

From NOAA SPC Derecho website

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SummarySummary

1.1. 2 types of mesoscale convective systems 2 types of mesoscale convective systems (mesoscale convective complex, squall line)(mesoscale convective complex, squall line)

2.2. Structure of MCCs Structure of MCCs

3.3. Structure of squall lines: four componentsStructure of squall lines: four components

1.1. Derechos. Definition (swath wider than 240 miles, Derechos. Definition (swath wider than 240 miles, wind speed>57 mph). 4 types (serial, progressive, wind speed>57 mph). 4 types (serial, progressive, hybrid, low dewpoint). Which state has the largest hybrid, low dewpoint). Which state has the largest annual number of derecho events? Most annual number of derecho events? Most derechos happen in the three months of May, derechos happen in the three months of May, June and JulyJune and July

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Works citedWorks cited

http://usatoday30.usatoday.com/weather/wcomform.htm http://usatoday30.usatoday.com/weather/wcomform.htm