3. Thunderstorms
– Violent convective storms with thunder and lightning
– Causes:
• Unstable Air and
Convection
• Clashing Air Masses
and Cold Fronts
• Convergence
3
4. Where would you expect the
most thunderstorms?
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18%
0%
0%
82% 1. Mid-latitudes
2. Polar Regions
3. Equatorial Regions
4. At the Sub-Tropical High
7. Which state would you expect to
have the most T-storms?
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9%
9%
0%
9%
0%
73% 1. Florida
2. Missouri
3. Colorado
4. Vermont
5. Oregon
6. New York
10. 10
Figure 7-29
• Lightning
– Electric discharge
– Separation of charges due
to friction with ice particles
– Release of electrons
– Lightning types
• Cloud to ground
• Cloud to cloud
• Within cloud
– Thunder
17. Thunderstorm Safety
• Take cover, stay there!
• Building is best. Car is 2nd (don’t touch
metal)
• Don’t BE or be UNDER the highest point
• Crouch on toes if out in open
• 5 second difference in lightning + thunder
arrival = 1 mile away
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19. Is a tornado a low or high
pressure system?
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18%
9%
73% 1. Low
2. High
3. Depends upon the individual storm
20. Tornadoes
• Tornadoes
– Small, intense cyclonic
storm (<400 meters across)
– Lowest central pressures,
very steep pressure gradient
– Fast winds, up to > 300 mph
– vapor and debris
20
Figure 7-30
22. Tornado formation
– Vertical wind shear creates horizontal rotation
– Tilted into vertical by thunderstorm updraft
– Mesocyclone and tornado development
22
23. Causes:
• Unstable air from clashing air masses
• Unstable air from convection or
convergence
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24. If cP air meets mT air, which will
rise?
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0%
0% 1. cP
2. mT
25. If mT air meets cT air, which will
rise?
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0%
0% 1. mT
2. cT
26. Which type of front will most
likely have a tornado?
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0%
0%
0% 1. Warm front
2. Cold front
3. Stationary front
29. Locations in US
• Tornado Alley
– clash between cP and mT
– Dry Line – cT meets mT
• Florida
– Convergence, Hurricanes, Convection
• Other Locations
– Convection, Cold Fronts
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33. Watch vs. Warning
• Watch - Conditions are conducive to the
development of tornadoes in and close to
the watch area.
• Warning - tornado has been sighted by
spotters or indicated on radar and is
occurring or imminent in the warning
area.
34. Danger signs
• Strong, continuous rotation in clouds
• Whirling dust and/or debris on ground beneath
cloud layer
• Hail or heavy rain followed by extreme shifts in
wind
• Loud, continuous rumble which doesn't fade
over time
• Bright, blue-green flashes near the ground of
power lines breaking
• Lowering of the clouds in a spiraling fashion
• Funnel cloud not moving toward left or right
35. Tornado Safety
• Mobile home or vehicle
– GET OUT and
AWAY!!
• Basement is best
• Or……under a stairwell
or in windowless room
or bathtub
• Cover yourself
42. • Tuscaloosa, AL 4/27/2011
• 1 minute raw footage – Tuscaloosa
• Joplin, MO 5/22/2011
• http://www.youtube.com/watch?
feature=endscreen&v=VQDkmziz1n8&NR
=1
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43. Why so many tornadoes
reported recently?
• More reporting and pictures captured!
• Many reported twice
• More people = more people impacted
• More people living in urban areas – when
they are hit, many are impacted
• 2011 was A particularly violent year –
favorable atmospheric conditions
• Climate change?
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