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Severe Weather

Severe Weather. Thunderstorms Tornadoes Hurricanes. Thunderstorm formation. Formed by strong upward movement of warm, unstable, moist air Cumulus clouds form single cloud Grow vertically Include lightning & thunder Usually produce rain. Storm over Mississippi. Winds in thunderstorm.

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Severe Weather

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  1. Severe Weather Thunderstorms Tornadoes Hurricanes

  2. Thunderstorm formation • Formed by strong upward movement of warm, unstable, moist air • Cumulus clouds form single cloud • Grow vertically • Include lightning & thunder • Usually produce rain

  3. Storm over Mississippi

  4. Winds in thunderstorm • Heating of the ground causes vertical motion of air • Weight of falling rain & cooling by evaporation cause downdrafts • Downdraft spreads, choking off the vertical motion • Cloud dies

  5. Types of Thunderstorms • Local • Mostly occur in spring or summer • Widely scattered • Photo: lake tahoe

  6. Types of Thunderstorms • Frontal • Often occur in lines along frontal surface • Squall line = formed ahead of front • Occur most often in spring & summer • May last several hours

  7. Lightning • Discharge of electricity • + at top; - at bottom of cloud • Temp of lightning flash ~ 28,000° C • Light travels 300,000 km / second • Sound travels .3 km / second • So… we see flash before rumble

  8. Thunderstorm Safety • Get indoors! • If you get stuck outside…crouch on the ground…do NOT stand under a tree

  9. Tornado • Narrow, funnel-shaped column of spiral winds that extends downward from the cloud base • Touches the ground

  10. Conditions • Strongest winds 360 – 800 km/hr • Winds move counterclockwise • Travels at speeds of 40 – 65 km/hr • Typically last an hour maximum • Accompanied by heavy rain, lightning & hail

  11. Tornado formation • Warm, moist air from the Gulf of Mexico moves N • Higher up, cool air moves east over Rocky Mtns.

  12. Tornado Safety • Get indoors • Basement, interior rooms, bathroom or closet • Outdoors? Find a ditch & lie flat & protect head

  13. Hurricane • Intense tropical low-pressure area • Sustained winds of 120 km/hr • Photo: hurricane Isabel, Oct 2003

  14. Hurricane formation

  15. Hurricane safety • Heed warnings! • Be prepared with radio, batteries, canned food & medicine

  16. Storm surge • Greatest damage associated with hurricanes is caused by the storm surge (Katrina in New Orleans) • Water piles up & winds blow it inland

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