Severe Weather Thunderstorms Lightening & Tornadoes Sixth Grade GPS Earth Science Pam 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

Lightning: an electric current many bits of ice bump into each other collisions create an electric charge cloud fills with electrical charges the positive charges form at the top the negative charges form at the bottom opposites attract causes a positive build up on ground beneath the cloud ZAP! Lightning Strikes!

Thunderstorms Lightning 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

Thunderstorms 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 SAFETY TIPS 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! Lightning may be about to strike if your hair stands up (feels prickly)

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 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!!

# Seconds / 5 = how many miles away 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 Tornado Warning Conditions are right for one to occur We’re watching for one! Tornado Warning One has been sighted Take cover!

Tornado SAFETY 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

change in wind direction How do tornadoes form? Wind shear change 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.

The Fujita Scale Theodore Fujita

What NOT to do (8 min video) http://www.youtube.com/watch?v=fDI3qdqabbE Moore, OK time-lapsed 3 min. http://www.youtube.com/watch?v=nfCj6v8JCY4

Where are tornadoes most likely to occur? 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".