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Severe Weather

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Severe Weather

  1. 1. PRECIPITATION & SEVERE WEATHER
  2. 2. Precipitation <ul><li>Rain </li></ul><ul><ul><li>microscopic ice crystals or water drops combine and become too heavy to stay suspended </li></ul></ul><ul><ul><li>ice crystals melt into rain as they fall through warmer layers of atmosphere </li></ul></ul><ul><li>Freezing Rain </li></ul><ul><ul><li>rain that freezes soon after hitting the ground </li></ul></ul><ul><ul><li>requires warm air mass above freezing ground temperatures </li></ul></ul>
  3. 3. <ul><li>Hail </li></ul><ul><ul><li>gusty winds blow rain upwards, freezing them </li></ul></ul><ul><ul><li>as strong winds repeatedly lift the droplets up, more ice gathers on them </li></ul></ul><ul><li>Sleet </li></ul><ul><ul><li>raindrops that freeze as they fall through a layer of freezing air below </li></ul></ul>
  4. 4. <ul><li>Snow </li></ul><ul><ul><li>ice crystals grow too heavy to remain suspended </li></ul></ul><ul><ul><li>stay frozen from cloud to ground level </li></ul></ul><ul><ul><li>grow larger when temps. are near freezing level </li></ul></ul><ul><ul><li>colder temps. produce smaller, powdery flakes </li></ul></ul>
  5. 5. Thunderstorms <ul><li>Begin with a strong updraft of air </li></ul><ul><ul><li>caused by cold front or any warm & moist air mass with cooler air around </li></ul></ul><ul><li>Towering cumulonimbus clouds </li></ul><ul><ul><li>can reach up to tropopause & flatten into anvil shape </li></ul></ul><ul><li>Heavy rain, sometimes hail, gusty winds, thunder & lightning </li></ul><ul><li>Storms form & dissipate quickly (30-45 min.) </li></ul><ul><li>video link </li></ul>
  6. 6. Lightning <ul><li>Electrons are picked up as falling ice crystals glance off other ice & rain drops </li></ul><ul><ul><li>negative charges build up at bottom of storm cell </li></ul></ul><ul><ul><li>positive charges left behind at the top of the cloud </li></ul></ul><ul><li>Air becomes ionized by strong electrical fields in clouds </li></ul>
  7. 7. <ul><li>Stepped Leader </li></ul><ul><ul><li>jerky, stepwise movement of negative charges towards earth </li></ul></ul><ul><li>Return Stroke </li></ul><ul><ul><li>positive charges rush up to meet the negative charges </li></ul></ul><ul><ul><li>brightest, hottest and loudest part of the lightning strike </li></ul></ul>
  8. 8. Cumulus Clouds
  9. 9. <ul><li>Sheet Lightning </li></ul><ul><ul><li>between or within clouds </li></ul></ul>
  10. 10. <ul><li>Lightning bolts </li></ul><ul><ul><li>up to 1 billion volts electricity </li></ul></ul><ul><ul><li>5x's hotter than sun's surface </li></ul></ul><ul><ul><li>kill 2,000 people each year </li></ul></ul><ul><li>Thunder </li></ul><ul><ul><li>extreme heat causes air to rapidly expand and vibrate </li></ul></ul><ul><ul><li>light travels faster than sound </li></ul></ul>
  11. 11. Tornadoes <ul><li>U.S. has most tornadoes in world </li></ul><ul><li>~ 1,000 each year in U.S. </li></ul><ul><li>most likely to occur April-June in late afternoon/evening </li></ul><ul><li>wind speeds of 50 - 300+ mph </li></ul><ul><li>Tornado Alley </li></ul><ul><ul><li>prime geographical area for twisters (centered around Texas, Oklahoma, and Kansas) </li></ul></ul>
  12. 12. <ul><li>An updraft forms from cold front moving south </li></ul><ul><ul><li>Cumulonimbus storm clouds form as warm/moist air meets cold/dry air </li></ul></ul><ul><li>Wind from another direction causes rising air to rotate </li></ul>
  13. 13. <ul><li>Fujita Scale </li></ul><ul><ul><li>F0 to F5 to rate intensity and destructiveness of a tornado </li></ul></ul>
  14. 14. <ul><li>Waterspout </li></ul><ul><ul><li>tornado over water </li></ul></ul><ul><li>Dust devil </li></ul><ul><ul><li>smaller, weaker version of a tornado (dry, not humid) </li></ul></ul>
  15. 15. Hurricanes <ul><li>Begin as huge thunderstorms over tropical seas </li></ul><ul><li>Rotation due to Coriolis effect </li></ul><ul><li>Rated by meteorologists </li></ul><ul><ul><li>tropical disturbance </li></ul></ul><ul><ul><li>tropical depression (23+ mph) </li></ul></ul><ul><ul><li>tropical storm (39+ mph winds) </li></ul></ul><ul><ul><li>hurricane (74+ mph) </li></ul></ul>Path of Hurricane Andrew 1992
  16. 16. <ul><li>Eye </li></ul><ul><ul><li>center of hurricane </li></ul></ul><ul><ul><li>low pressure center </li></ul></ul><ul><ul><li>about 10 miles wide </li></ul></ul><ul><ul><li>calm winds, sunny skies </li></ul></ul><ul><li>Rain Bands </li></ul><ul><ul><li>lines of thunderstorm cells rotating around the eye </li></ul></ul><ul><ul><li>spiral slowly inward, becoming more intense near the eye </li></ul></ul>
  17. 17. <ul><li>Extend up to 600 miles across </li></ul><ul><li>Move 10-20 mph (over water), pushed by prevailing winds </li></ul><ul><li>Weaken over land into thunderstorms (lack of warm/moist air) </li></ul><ul><li>Categorized based on wind speed and destructiveness </li></ul>
  18. 18. <ul><li>Damage from: </li></ul><ul><ul><li>high winds (up to 200 mph) </li></ul></ul><ul><ul><li>storm surge flooding (ocean levels 25 ft above normal) </li></ul></ul><ul><ul><ul><li>caused by high winds & hurricane eye's low pressure &quot;bulge&quot; </li></ul></ul></ul>

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