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Thunderstorms

Chapter 14. Thunderstorms. 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.

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Thunderstorms

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  1. Chapter 14 Thunderstorms

  2. 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

  3. A dissipating thunderstorm

  4. 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

  5. Multicell storm

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

  7. Dust clouds from microbursts

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

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

  10. Shelf cloud

  11. Thunderstorms • Multi-cell Thunderstorms • Squall-line thunderstorms; line of multi-cell thunderstorms, pre-frontal squall-line, derecho

  12. Pre frontal Squall line

  13. Pre frontal Squall line

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

  15. 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, 10,000km2

  16. 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

  17. A supercellthunderstormwith a tornado sweeps over Texas

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

  19. Thunderstorms • Supercell thunderstorms • Cap and convective instability

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

  21. Fig. 14-23, p. 384

  22. 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 moving thunderstorm

  23. downtown Des Moines, Iowa, during July, 1993 Fig. 14-25, p. 387

  24. 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 • Slow moving Thunderstorm

  25. Fig. 1, p. 386

  26. 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)

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

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