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Weather and Climate

Weather and Climate

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Weather and Climate

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  1. Weather and Climate Lecture 13: Severe Weather and Hurricanes

  2. Thunderstorms • A thunderstorm is simply a storm containing lightning and thunder. • Thunderstorms occur all over the world

  3. Formation - Ingredients • Moisture (water vapor) in the lowest levels of the atmosphere • Cold, dry air aloft (2-3 miles above the surface) • Lifting mechanism

  4. Air Mass (Single-Cell) Thunderstorms • Formed by uneven heating of the earth’s surface • Brief, but well-defined lifespan with three stages • Cumulus Stage • Mature Stage • Dissipating Stage

  5. Three Stages

  6. Mature Thunderstorms • The updraft can become so strong that it penetrates into a region of stable air, resulting in a overshooting top.

  7. Overshooting Tops

  8. Which is mature and which is dissipating?

  9. Lifespan of a Thunderstorm • A single cell, consisting of an updraft and downdraft, lasts 20 minutes. • But we have all observed thunderstorms that appear to last longer than 20 minutes…. WHY?

  10. Multicell Storms • Sometimes when the cold downdraft reaches the surface, it may force the warm, moist surface air upward • This rising air can condense and build a new thunderstorm Multicell Cluster Multicell Line (Squall Line)

  11. Downdrafts

  12. Gust Fronts

  13. Gust Front

  14. Downbursts

  15. Straight-Line Winds • Associated with a cluster of severe thunderstorms • May exceed 90 knots • If wind damage extends 250 miles along storm path, it is called a derecho.

  16. Tree Damage What does it look like from a downburst vs. a derecho?

  17. What makes a thunderstorm a severe thunderstorm?

  18. Severe Thunderstorm • Hail ¾” or greater • Winds in excess of 50 knots (57.5 mph) • Tornado

  19. Severe Thunderstorms

  20. Supercell Thunderstorms

  21. Capping Inversion • An important component of creating a severe thunderstorm is the strength of the boundary layer cap. • Too strong nothing develops • Too weak numerous cumulus clouds • Just righthelps to funnel the air into a strong updraft

  22. Supercell Thunderstorms

  23. Squall Line

  24. Squall Line

  25. Dry Line

  26. Tornadoes

  27. Tornadoes

  28. Tornadoes

  29. Tornado Alley

  30. Tornado Wind Speed As the tornado moves along a path, the circular tornado winds blowing opposite the path of movement will have less speed. For example, if the storm rotational speed is 100 knots, and its path is 50 knots, it will have a maximum wind of 150 knots on its forward rotation side. Figure 15.31

  31. Suction Vortices • Many violent tornadoes contain small whirls inside them.

  32. Tornadoes vs. Mesocyclone • Development of mesocyclone • Stretching – gives rotating air a faster spin

  33. Supercell View from East

  34. Tornadoes • Vertical Wind Shear (pencil example) • Horizontal roll meets updraft and is tilted vertically

  35. Rotating Clouds as Tornado Signal The first sign that a supercell may form a tornado is the sight of rotating clouds at the base of the storm, which may lower and form a wall cloud, shown in this picture. Figure 15.41

  36. Tornadoes

  37. Position

  38. Fujita Scale

  39. Tornadoes and Corn

  40. Modeling Thunderstorms

  41. Modeling Thunderstorms

  42. Lightning

  43. Cloud to Ground

  44. Cloud to Cloud