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Chapter 7: Atmospheric Disturbances

Chapter 7: Atmospheric Disturbances. Part II: T-storms, Tornadoes, Lightning & Forecasting. Nature of T-storms Violent Thunder & lightning Hail Strong updrafts & downdrafts T-storm formation stages Cumulus stage Mature stage Dissipating stage. Localized Severe Weather.

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Chapter 7: Atmospheric Disturbances

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  1. Chapter 7: Atmospheric Disturbances Part II: T-storms, Tornadoes, Lightning & Forecasting

  2. Nature of T-storms Violent Thunder & lightning Hail Strong updrafts & downdrafts T-storm formation stages Cumulus stage Mature stage Dissipating stage Localized Severe Weather Figures 7-28 & 7-25

  3. Days with t-storms by latitude: Figure 7-26 Localized Severe Weather • Thunderstorms • Atmospheric conditions for t-storm formation • High temperatures • High humidity • High instability Days per year with t-storms in U.S.: Figure 7-26

  4. 6-13-2004 Supercell

  5. What it looked like under the supercell on 6-13-2004

  6. Localized Severe Weather Figure 7-30 • Tornadoes • Deep low pressure vortex • Winds so violent, vacuum develops inside funnel • May be in excess of 300 mph • Most extreme pressure gradients known • Don’t know exact mechanism of formation • Warm, moist, unstable air • Spring & summer = most favorable • Most occur in mid-afternoon • Time of max heating

  7. Localized Severe Weather • Tornado formation • Vertical wind shear creates horizontal rotation • Horizontal rotation tilted vertical by updrafts • Mesocyclone& tornado development Figure 7-31

  8. Localized Severe Weather • Over 90% of reported tornadoes worldwide occur in the U.S. Figure 7-33 Figure 7-32

  9. It’s all a matter of statistics: Who has the worst tornadoes?

  10. 8-28-1884 Howard, SD

  11. Localized Severe Weather: Tornado Myths • Safest location in a building • Opening windows to reduce damage • Using highway overpasses as shelter • Escaping a tornado in a vehicle • Tornadoes “skip” houses • Association of size with intensity • Appearing to reach the ground • Direction of travel • Geographical scope • Near various landscape features • Attraction to mobile homes and/or trailer parks • Downtown areas • During winter

  12. April 2011 Tornado Outbreak

  13. Hallam, NE (2004)

  14. Omaha’s 1913 Easter Tornado

  15. Localized Severe Weather • Lightning • 8.5 million bolts daily • Electric discharge in t-storms • Lightning types • Cloud to ground • Cloud to cloud • Within cloud • Thunder • Expansion of air from heat of lightning • Time lightning distance • Speed of sound vs. speed of light • Every 5 seconds equals about 1 mile Figure 7-29

  16. Localized Severe Weather: Forecasting • Oklahoma – most tornadoes worldwide • Vertical wind shear • Change in wind direction from storm’s bottom to top • Mesocyclones • 50% develop into tornadoes • NEXRAD • Doppler effect • Vertical wind profiler • Dryline: boundary between mT & cT air • OK Mesonetwork: • 111 solar-powered weather stations

  17. Localized Severe Weather: Forecasting with NEXRAD Figure 7-E: Reflectivity = Storm intensity Tornado warning issued Figure 7-F: Motion detection = Funnel I.D.

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