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Thunderstorms

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Thunderstorms

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    1. Thunderstorms

    2. Thunderstorms

    3. Thunderstorms a storm containing lightning and thunder, towering cumulonimbus clouds. They do not generally rotate (non-cyclonic). They are associated with midlatitude cyclones, localized convection, orographic lifting and tropical cyclones.

    4. Thunderstorm Formation Ingredients warm, moist air (often mT) unstable (or conditionally unstable if lifting mech.) encouraged by diverging air aloft

    6. Thunderstorm Life Cycle

    7. The Geography of Thunderstorms

    9. Thunderstorm Frequency Probably 1500 to 2000 thunderstorms active around the world at any given time.

    10. Hail Downbursts (Microbursts) Lightning and thunder Tornadoes Violent Associations

    11. Hail Formation Layer upon layer of ice and water in high speed thunderstorm cloud convection cycle

    12. Downbursts Macrobursts - extreme downdrafts associated with thunderstorms. Microburst smaller < 5 minute duration winds up to 146 mph

    13. Lightning discharge of electricity that occurs in mature thunderstorms Cause: charge separation in cloud sets up electrical potential

    14. Frequency of Occurrence Globally, lightning flashes ? 100 times per second.

    15. Geography of Lightning

    16. USA: Real-time Lightning

    17. Thunder Air poor conductor of electricity Huge electrical potential develops Lightning bolt ‘superheats’ the air (30,000?C, 54,000 ?F) Surrounding air expands violently ? sound wave

    18. Distance from the Thunderstorm Speed of light: 186,000 m/s Speed of sound: about 1000 ft/s or 1/5 mile/s Distance calculation for each 5 seconds, about 1 mile away

    19. Key Points Thunderstorm formation and life cycle Thunderstorm geography and frequency Violent associations hail, downbursts, lightning/thunder next lecture….tornadoes

    20. Tornadoes Tornado Clip

    21. Tornado Formation Severe “Super Cell” Thunderstorm (1% spawn tornadoes) Often occur along cold fronts and move to NE Strong updrafts Wind shear (abrupt change in direction or strength of winds) top to bottom of storm)

    22. Funnel Cloud v. Tornado

    23. Waterspout - over water - less power - smaller temp gradient

    24. World Tornado Geography USA: 90%+ of all tornadoes

    25. USA Tornado Geography Every state! Tornado Alley (TX, OK, KS, NE)

    27. USA Tornado Season

    28. St. Louis Tornadoes By Hour

    29. USA Tornado Occurrence

    30. Tornado Classification Fujita F-scale F0 (winds < 120 mph) to F5 (winds 200-300+ mph) based on rotational wind speed and damage done Size: Tornadoes generally < 1/4 mile wide (damage path only 150 ft.)

    31. Deadliest Tornados U.S.A. Tri-state tornado outbreak of March 18, 1925 Kills 689 people in Missouri, Illinois & Indiana World April 26, 1989 - Bangladesh - claimed 1,300 lives. Largest Tornado Outbreak April 3-4, 1974 Super-Outbreak 148 tornadoes overnight across 11 states.

    32. Tornado Forecasting NEXRAD doppler radar (WSR-88D) 138 stations across the USA Intensity of storm noted by amount of reflection off rain, hail, and ice crystals. Hook cloud is an indicator.

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