Severe Weather

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Severe Weather

• 20.3

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Thunderstorms

• How to make a thunderstorm
• Moisture to form clouds and rain
• Unstable air relatively warm air that can rise
  rapidly
  
• Lift force air to rise cool condense cloud

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What causes the LIFT?

• Fronts - mainly COLD fronts
• Sea-breezes
• Mountains - act as a ramp

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Time Frame

• More common in afternoon and evening (why?)
• Earths surface reaches its max during
  mid-afternoon - heat fuel for storm
  
• More common during spring/summer
• Heat fuel for storm

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3 stages

• Towering cumulus cloud
• Little rain if any
• Lasts about 10 minutes

- Most likely time for hail, heavy rain,
lightning, strong winds tornadoes
- May have a black or dark green appearance
- lasts about 10 20 minutes

• Rainfall decreases
• Some thunderstorms produce a burst of strong
  winds
  
• Lightning remains a danger

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Severe Thunderstorms

• Super strong updrafts downdrafts
• Intense rotating updrafts
• Can last for several hours
• - updrafts as strong as 150 mph

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Lightning

• The action of rising and descending air within a
  thunderstorm separates positive and negative
  charges.
  
• Lightning results from the buildup discharge of
  electrical energy between positively negatively
  charged areas.

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• Most lightning happens WITHIN a
• cloud (intra-cloud) 90

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• There is an invisible channel of air (step
  leader) that moves from the cloud down to the
  ground and from the ground up to the cloud
  
• When they meet, illumination occurs (return
  stroke)
  
• from the ground up!

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Lightning Facts

• Lightning is 50,000 degrees (hotter than the
  surface of the sun)
  
• Fulgurite lightning that hit a beach - turns
  the sand to glass
  
• Lightning starts 9000 forest fires/year
• Lightning accounts for 300 injuries 90
  deaths/year
  

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Thunder

• Lightning heats surrounding air
• The rapid expansion and contraction creates a
  shock wave
  
• (we hear as sound)
• When you see lightning, then count in seconds
  until you hear thunder.
  
• 5 seconds per mile

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Safety

• Stay inside - no contact with water from pipes or
  corded electronics. Electricity flows through
  plumbing and wires.
  
• Stay in your car if you are already there -
  lightning will go around the metal shell of the
  car
  

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• If outside - go to a low area away from tall
  objects water - (no boating)
  
• Lightning can travel from person to personso
  keep at least 15 from other people
  
• Avoid metal fences or poles, trees, picnic
  shelters or buildings that stand alone
  
• NEVER take shelter under a tree to keep dry!!!!

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• If skin tingles or your hair stands up,
  immediately put your feet together, crouch down,
  tuck you head and cover your ears - try to have
  as little contact with the ground as possible.
• In this picture the young woman and her friends
  were severely injured by lightning just a few
  seconds after this picture was taken. Notice that
  no rain was falling, clearly illustrating that
  lightning can strike up to several miles away
  from the thunderstorm.
• Dont resume outdoor activity until half an hour
  after the thunder lightning has stopped

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• Heat lightning just a distant storm thats so
  far away you cant really hear the thunder
  
• It can lightning in a snowstorm, but its rare
• Lightning can kill - usually indirectly
• Just because it stopped raining, lightning still
  occurs.
  
• Show lightning video

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Heat Wave

• As humidity increases, it is harder to cool
  through evaporation.
  
• This can lead to serious health problems
  heatstroke, sunstroke, death
  
• Heat Index developed to help warn
• Heat index is how the temperature feels with
  the humidity
  

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Cold Wave

• Extended periods of below-normal temperatures.
• Wind transports heat away from the body - which
  worsens the affects of the cold air
  
• Wind-Chill Index was developed to help
• Wind-chill is what the temperature feels like
  with the wind - NOT what it actually is.
  

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Tornado

• A tornado is a violent rotating column of air
  extending from a thunderstorm to the ground.
  
• The most violent tornadoes are capable of
  tremendous destruction with wind speeds of up to
  300 mph.
  
• They can destroy large buildings, uproot trees
  and hurl vehicles hundreds of yards. They can
  also drive straw into trees.
  
• In an average year, 1000 tornadoes are reported
  nationwide

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Tornado Variations

• May appear nearly transparent until dust and
  debris are picked up
  
• Occasionally, two or more tornadoes may occur at
  the same time
  
• Waterspout weak tornadoes that form over warm
  water

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waterspout
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Rotating wall cloud is often nearly rain-free
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Counterclockwise and in / up
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F0
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F1
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F2
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F3
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F4
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F5
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• Most weak tornadoes last 10 minutes or less
  travel short distances
  
• Violent tornadoes have been known to last for
  hours a few have traveled more than 100 miles.

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Tornado Watch The conditions are right for a to
rnado to form. Watch outkeep your eyes and ears
tuned in.

Tornado Warning There has been a tornado spotted
. Take shelter immediately.
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Watch for Tornado Danger Signs
Dark, often greenish sky Wall cloud Larg
e Hail
Cloud of debris Roaring noise
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If Indoors Go to a safe place to protect yourse
lf from glass and other flying objects. The
safest place to take shelter during a tornado is
in a basement that does not have windows.
If there is no basement, go to the lowest floor
and take shelter in a hallway, bathroom, closet
or small room toward the inside of the building
and away from windows. Get under a piece of stu
rdy furniture and hold on to it. Heavy furniture
can help protect you from falling debris.
If youre not at home, go to a basement or
low-level hallway or room, and avoid places with
wide-span roofs such as auditoriums, cafeterias,
large hallways, or shopping malls.
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If Outdoors If possible, get inside a building.
If shelter is not available, or if there is no
time to get indoors, lie in a ditch or low-lying
area or crouch near a strong building. Be aware
of potential flooding. Do not go under bridges
and overpasses dangerous flying debris can be
blown under the overpass and weakened overpasses
or bridges can be destroyed.
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Hurricane

• Whirling tropical cyclone - winds at least 74
  mph
  
• Hurricane in Atlantic Ocean
• Typhoon in Pacific Ocean
• Hurricane Season mid August through
• November

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Storm Surge winds drive a mound of water inward
floods!
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Typical Hurricane Life Story

• Day one Thunderstorm growing
• Day three Tropical Depression (
• Day five Tropical Storm (34 73 mph)
• Day seven Hurricane (74mph)
• Day twelve Hurricane weakens after hitting land

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