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Severe Weather Thunderstorms
Lightening & Tornadoes
Sixth Grade
GPS Earth SciencePam Myers
THUNDERSTORMS Caused by quick, upward
movement of warm, moist air
Occurs along a cold front within a warm air mass
Air is heated by Earth’s surface
Thunderstorms
Lightning• Produced by electrons• Flows from a negatively-charged area• To a positively-charged area
• cloud fills with electrical charges• the positive charges form at the top• the negative charges form at the
bottom
Lightning: an electric current• many bits of ice bump into each other
• collisions create an electric charge
• opposites attract• causes a positive build up on ground
beneath the cloud• ZAP! Lightning Strikes!
ThunderstormsLightning• Either in a cloud or on the ground• Causes air to expand rapidly – bright flash
• Ground’s electrical charge concentrates around anything that sticks up
• The charge coming up eventually connects with a charge reaching down from the clouds
Thunder• Caused by rapid expansion of air
• Produced by lightning bolt
• If you hear the sound of thunder, then you are in
danger from lightning.
• Lightning kills/injures more people each year than
hurricanes or tornadoes (between 75 -100 people)
Thunderstorms
You Must Avoid. . . . . . . – using electrical appliances (includes telephone)
– being near tall objects (like under a tree)
– open spaces (crouch down and hug your knees
– being near or in bodies of water
– all conductors of electricity!
ThunderstormsSAFETY TIPS
Lightning may be about to strike ifyour hair stands up (feels prickly)
Which do you think is hotter, a bolt of lightning, or the surface of the sun?Lightning- it is 30,000 degrees
Celsius. That’s 5 times hotter than the sun!!
Thunder Is Caused By Lightning
Lightning bolt travels (cloud to ground) Opens a channel (a little hole in the
air) Super heated air expands
Quickly cooled air collapses back due Sound wave is thunder Light travels faster than sound Lightning before we thunder
Can you tell how far away a thunderstorm is?
• Count the number of seconds between when you see lightning & hear thunder
# Seconds / 5 = how many miles away
For example:
If you counted 10 seconds between the lightning and the thunder, the lightning is 2 miles away!
TORNADO(Twister or Whirlwind)
Rotating, funnel-shaped cloud Usually Midwestern USA Diameter: several hundred yards Develops during a thunderstorm Air Pressure
– Rapid drop– causes rain & hail
Wind speed ranges 40-370 mph Lasts about 10 minutes (THANK GOODNESS!)
TORNADO
Tornado Watch– Conditions are right for one to
occur– We’re watching for one!
Tornado Warning−One has been sighted−Take cover!
TornadoSAFETY TIPS
Move to underground area (basement) If outdoors, get in a ditch -- not under a bridge If no basement, lie flat beneath a table or bed Go to central part of building Stay away from windows Get out of car or mobile home Crouch in the SW corner
– debris usually fall in the NE corner
http://www.srh.noaa.gov/oun/?n=safety-overpass-slide11
How do tornadoes form?
Wind shearchange in wind direction an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in lower atmosphere
Rising air from the updraft of a thunderstorm tilts the rotating air from horizontal to vertical.
An area of rotation, 2-6 miles wide, now extends through
much of the storm.
http://www.youtube.com/watch?v=fDI3qdqabbEWhat NOT to do(8 min video)
http://www.youtube.com/watch?v=nfCj6v8JCY4Moore, OK time-lapsed 3 min.
The Great Plains of the central the United States brings ingredients together.
includes TX, KS, and OK.
More than 500 tornadoes in this area annually , commonly known as "Tornado Alley".
Where are tornadoes most likely to occur?
