1. Meteorology
Unit 5 - Tornadoes

2. What is a tornado?
Tornado – a violently destructive windstorm, characterized by a long, funnel-shaped cloud extending toward the ground and made visible by condensation and debris
Almost all tornadoes rotate counterclockwise around a central core of low pressure
A few have been seen rotating clockwise, but this is extremely rare

4. Tornado AKA Also called twisters or cyclones
Funnel cloud – tornado that has not reached the ground
Waterspout – a rotating column of air over a body of water

5. Tornado Structure Diameter between 300 – 2,000 feet
Few have been over 1 mile wide
2004, Nebraska – 2.5 miles wide
Usually travel mph, some clocked at 70+ mph
Usually only last a few minutes and have an average path length of 4 miles
1917, tornado traveled 292 miles through Illinois and Indiana over a 7 hours

7. Tornado Life Cycle
Dust-whirl Stage – dust swirling up from the ground marks the tornadoes circulation and a short funnel extends from thunderstorm’s base
Organizing Stage – tornado increases in intensity, funnel extends downward
Mature Stage – Funnel reaches its greatest width and contacts ground. Vertical. This is the stage where the most damage occurs
Shrinking Stage – decrease in funnel width, narrowing in path, tornado may tilt. Still can cause severe damage.
Decay Stage – tornado looks rope-like and eventually dissipates

9. Tornado Formation
Form with intense thunderstorms and conditionally unstable environments
Usually with supercell storms with strong wind shear
Rotating air may begin in the storm and work downward or begin on the ground and work upwards
Fueled by convective circulation of warm updrafts and cold downdrafts

10. Vortex Tube
Strong updrafts form a vortex tube. If updrafts tilt and pull the vortex tube into the storm, it becomes a rotating air column within the storm

11. Vortex Tube

12. Tornado Occurrence
Occur in many parts of the world, but most common in the United States
USA averages more than 1,000 yearly
Record 1722 tornadoes in 2004
Greatest number occur in Tornado Alley in central US
Tornado Alley often provides the right atmospheric conditions

15. Tornado Occurrence Most tornadoes occur between March and July
Greatest number occur in May, but the strongest tornadoes usually occur in April
Most frequent between 4:00-6:00pm

16. Tornado Measurement
Fujita Scale – original scale, wind speed was estimated based on damage to surface
Enhanced Fujita Scale (EF Scale) – using 28 different criteria, still uses damage to determine wind speed
EF0: 65-85mph
EF1: mph
EF2: mph
EF3:136 – 165mph
EF4: mph
EF5: >200mph

17. The majority of tornadoes are weak at EF0 or EF1
The majority of tornadoes are weak at EF0 or EF1. The United usually has one or two EF5 tornadoes each year

22. Strange Occurrences
People, animals, and machinery picked up, carried, and (mostly) safely deposited miles away
Railroad coach with 117 passengers was picked up and moved 80 feet
Schoolhouse was demolished and the 85 students inside were carried 300+ feet with no fatalities
Showers of fish or frogs have fallen over land after tornadoes took them from water
Chickens losing all their feathers
A piece of straw driven through a metal pipe
Frozen hot dogs being driven though concrete walls

29. What do I do? Seek shelter, preferably in a basement or interior room
Stay away from windows
Find a shield, like a mattress
If outside, lay flat in a depression or ravine and cover your head
If in a vehicle, do not try to outrun the tornado. Stop and try to move perpendicular to the tornado.
Listen to the radio/TV for tornado watches and warnings

31. Tornado Myths Opening windows will keep the house from exploding
Was once thought to help equalize pressure
Now known it actually increases pressure on the opposite wall and increases chance the building will collapse
Damage is mostly caused by wind and debris, not pressure
Take shelter under a highway overpass or bridge
Winds are actually funneled and strengthened by the overpass/bridge structure