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Localized Severe Weather Easterly Waves, Thunderstorms and Tornadoes

Localized Severe Weather Easterly Waves, Thunderstorms and Tornadoes. Ch 7 pt 2: Localized Atmospheric Disturbances. Source: NOAA Photo Library http://www.photolib.noaa.gov/collections.html. Fig. 7-19. Easterly Waves Formation Path Non-cyclonic Convergence Relationship to Hurricanes.

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Localized Severe Weather Easterly Waves, Thunderstorms and Tornadoes

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  1. Localized Severe Weather Easterly Waves, Thunderstorms and Tornadoes Ch 7 pt 2: Localized Atmospheric Disturbances Source: NOAA Photo Library http://www.photolib.noaa.gov/collections.html

  2. Fig. 7-19 Easterly Waves Formation Path Non-cyclonic Convergence Relationship to Hurricanes Minor Tropical Disturbances: Easterly Waves

  3. Localized Disturbances • Thunderstorm: violent, convective storm accompanied by thunder and lightning • Vertical air motion, humidity, and instability • Stages • 1) Uplift of warm, moist air • 2) cumulus stage • 3) mature stage • 4) dissipating stage • Fig. 7-31

  4. Fig. 7-28 Sequential Development

  5. Fig. 7-29 Frequency by latitude (per year)

  6. Lightning • Over 8.5 million lightning bolts daily • Thunder: instantaneous expansion of air caused by the abrupt heating that lightning bolts produce • Can time the distance that lightning is away • Differing rates: speed of sound vs. speed of light • Every 5 seconds equals about a mile

  7. Near Hallam, NE (5-22-04)

  8. Tornadoes • Tornado: localized cyclonic low-pressure cell surrounded by a whirling cylinder of wind spinning so violently that partial vacuum develops within the funnel • Most extreme pressure gradients known; what produces such extreme winds • We don’t know exact mechanisms of formation • warm, moist, unstable air; often along a cold front • Spring and summer are most favorable • Most occur in mid-afternoon (time of max. heating) • Over 90% of reported tornadoes occur in the U.S.

  9. Tornado Formation • Fig. 7-33

  10. Distribution of Tornadoes Figure 7-36

  11. Fig. 7-30 Frequency of hailstorms in the United States (per year) Seasonality

  12. Classification

  13. 8-28-1884 Howard, SD

  14. Tornado Myths • Myth #5: Highway overpasses are a safe place to shelter if you are on the road when you see a tornado coming. • Myth #4: Opening windows to equalize air pressure will save a roof, or even a home, from destruction by a tornado. • Myth #3: Tornadoes never strike big cities. • Myth #2: Some towns are "protected!" • Myth #1: The southwest corner of a basement is the safest location during passage of a tornado.

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