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Chapter 14. Wall Cloud associated with a super cell thunderstorm.

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Presentation on theme: "Chapter 14. Wall Cloud associated with a super cell thunderstorm."— Presentation transcript:

1 Chapter 14

2 Wall Cloud associated with a super cell thunderstorm

3 Thunderstorms A storm containing lightening and thunder; convective storms may have heavy rain hail Ordinary Cell Thunderstorms Air-mass thunderstorms: limited wind sheer Stages: cumulus, mature, dissipating Entrainment, downdraft, gust front


5 A dissipating thunderstorm

6 Thunderstorms Multi-cell Thunderstorms Thunderstorms that contain a number of convection cells, each in a different stage of development, moderate to strong wind shear; tilt, over shooting top

7 Multicell storm

8 Thunderstorms Multi-cell Thunderstorms Micro-bursts: localized downdraft that hits the ground and spreads horizontally in a radial burst of wind; wind shear, virga

9 Dust clouds from microbursts

10 Thunderstorms Multi-cell Thunderstorms Gust Front: leading edge of the cold air out- flowing air; shelf cloud, roll cloud, outflow boundary


12 Thunderstorms Severe thunderstorms: one of large hail, wind gusts greater than or equal to 50kts, or tornado, tilted updraft/downdraft

13 Shelf cloud



16 Thunderstorms Multi-cell Thunderstorms Squall-line thunderstorms; line of multi-cell thunderstorms, pre-frontal squall-line, derecho

17 Pre frontal Squall line


19 Pre frontal Squall line



22 The thunderstorms are producing strong straight-line winds called a derecho

23 Thunderstorms Multi-cell Thunderstorms Meso-scale Convective Complex: a number of individual multi-cell thunderstorms grow in size and organize into a large circular convective weather system; summer, 10,000km 2


25 Thunderstorms Supercell thunderstorms Large, long-lasting thunderstorm with a single rotating updraft Strong vertical wind shear Outflow never undercuts updraft Classic, high precipitation and low precipitation supercells Rain free base

26 A supercell thunderstormwith a tornado sweeps over Texas



29 Thunderstorms Supercell thunderstorms Strong vertical wind shear Surface, 850mb, 700mb, 500mb, 300mb conditions low-level jet


31 Thunderstorms Supercell thunderstorms Cap and convective instability


33 Thunderstorms Thunderstorms and the Dryline Sharp, horizontal change in moisture Thunderstorms form just east of dryline cP, mT, cT

34 Fig , p. 384

35 Thunderstorms Floods and Flash Floods Large floods can be created by training of storm systems, Great Flood of 1993 Flash floods rise rapidly with little or no advance warning; many times caused by stalled or slow thunderstorm


37 Fig , p. 387 downtown Des Moines, Iowa, during July, 1993

38 Thunderstorms Topic: Big Thompson Canyon July 31, 1976, 12 inches of rain in 4 hours created a flood associated with $35.5million in damage and 135 deaths

39 Fig. 1, p. 386

40 Flash Floods Slow moving or Stalled thunder Storm, especially in canyon areas 135 deaths in 1976 flood 12 inches of rain in 4 hours (normal ~16 inches /year)




44 Thunderstorms Distribution of Thunderstorms Most frequent Florida, Gulf Coast, Central Plains Fewest Pacific coast and Interior valleys Most frequent hail Central Plains








52 Thunderstorms Lightening and Thunder Lightening: discharge of electricity in mature storms (within cloud, cloud to cloud, cloud to ground) Thunder: explosive expansion of air due to heat from lightening Electrification of Clouds: graupel and hailstones fall through supercooled water, ice crystals become negatively charged Upper cloud positive, bottom cloud negative





57 Thunderstorms Observations: Elves Blue jets, red sprite, ELVES

58 Fig. 2, p. 390

59 Thunderstorms The Lightening Stroke Positive charge typically on ground, cloud to ground lightening Stepped leader, ground stroke, forked lightening, ribbon lightening, bead lightening, corona discharge


61 Thunderstorms Observation: Apple tree DO NOT seek shelter during a thunderstorm under an isolated tree. Lightening Detection and Suppression Lightening direction finder detects radiowaves produced by lightening, spherics National Lightening Detection Network Suppression: seed clouds with aluminum


63 Fig. 3, p. 395

64 Fig , p. 392

65 Fig , p. 393


67 Fig , p. 393 fulgurite

68 Fig , p. 394

69 Fig , p. 394 sferics


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