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Severe Weather

Severe weather phenomena, including thunderstorms, tornadoes, and hurricanes, result from complex atmospheric conditions. Thunderstorms form from strong upward movements of warm, moist air and typically produce rain, lightning, and thunder. Tornadoes are intense, funnel-shaped winds that can reach speeds of 800 km/h, while hurricanes are characterized by sustained winds of 120 km/h and are often preceded by a storm surge that can cause significant damage. Understanding their formation, behavior, and safety precautions is crucial for preparedness.

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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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