Severe Weather

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Severe Weather

• Thunderstorms
• Tornadoes
• Hurricanes

http//www.txdirect.net/msattler/tornado.htm
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Thunderstorms

• Usually occur along a cold front, when cold air
  meets warm air
• Cold air forces warm air upward, creating a
  cumulonimbus cloud as water vapor cools and
  condenses

http//www.usatoday.com/weather/tg/wcfront/wcfront
.htm
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Thunderstorms

• Rapidly rising warm air generates an updraft
• Cool air sinks, resulting in a downdraft
• Hail and/or downpours often accompany downdrafts

http//www.xtremewx.com/StormStages.htm
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Fig. 11.7
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THUNDERSTORM CUMULUS STAGE

• CUMULUS STAGE
• REQUIRES CONTINUOUS SOURCE OF WARM MOIST AIR
• EACH NEW SURGE OF WARM AIR RISES HIGHER THAN THE
  LAST
• STRONG UPDRAFTS

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THUNDERSTORM MATURE STAGE

• SHARP COOL GUSTS AT SURFACE SIGNAL DOWNDRAFTS
• UPDRAFTS EXIST SIDE BY SIDE WITH DOWNDRAFTS
• IF CLOUD TOP REACHES TROPOPAUSE UPDRAFTS SPREAD
  LATERALLY - ANVIL SHAPE
• TOP OF ICE LADEN CIRRUS CLOUDS
• GUSTY WINDS, LIGHTNING, HEAVY PRECIPITATION, HAIL

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THUNDERSTORM DISSIPATING STAGE

• DOWNDRAFT DOMINATES
• NO UPDRAFT
• THUNDERSTORM LOSES ENERGY SOURCE

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Fig. 11.7
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Hail

• Hail is the result of water droplets being
  uplifted repeatedly within the storm cloud
• The more unstable the air, the larger the hail

http//www.physicalgeography.net/fundamentals/imag
es/hail_formation_model.jpg
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Lightning

• Ice, water dust collide and build up static
  electricity
• Electrical charges accumulate and discharge as
  lightning

http//www.usatoday.com/weather/wtsm0.htm
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LIGHTNING

• .LARGE ELECTRICAL DISCHARGE THAT RESULTS FROM
  RISING AND SINKING MOTIONS IN A THUNDERSTORM
• .SEQUENCE IS AS FOLLOWS
• . CHARGE SEPARATION - REALLY DO NOT UNDERSTAND
  WHY
• . GROUND BECOMES POSITIVELY CHARGED
• . LIGHTNIING FORMATION BEGINS - LEADERS
• . LIGHTNING FLASH OCCURS

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Lightning formation Charge separation.
Fig. 11.28
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Thunder

• The extreme heat of lightning causes air to
  expand rapidly ? Thunder
• It takes thunder 5 seconds to travel 1 mile,
  while the light from lightning reaches you almost
  instantly.
• Suppose you see a flash of lightning. If it
  takes 15 seconds for you to hear the thunder, how
  far away is the lightning?

Answer 3 miles!
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Tornadoes

• Tornadoes form in the updraft of a supercell
  thunderstorm
• A vortex results and sends spinning air down from
  the cloud
• The center of a tornado has very low pressure
• Usually form in late spring or early summer

http//van.hep.uiuc.edu/van/qa/section/Everything_
Else/Weather/925172403.htm
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Wind speed Fujita class are estimated by damage
caused by the tornado
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Hurricanes

• Originate in the East Atlantic off Africas coast
• Tropical wave ? Tropical depression ? Tropical
  Storm ? Hurricane (74 mph sustained winds)
• Center (the eye) is calm and clear

http//www.wildweather.com/gallery/photoMichelle-7
.htm
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Hurricanes

• Category 1-5 on the Saffir-Simpson scale

http//www.woodwardem.org/files/Hurricane_Scale.jp
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