1. Tornadoes

2. Tornado
A violently rotating column of air (vortex), hanging from a cumulonimbus cloud, with circulation that touches the surface of the earth

3. Other Names for Tornadoes
Tornado comes from the Spanish word, tronada, which means “thunderstorm.”
twisters, dust devils, whirlwinds, waterspouts, and cyclones

4. Waterspouts
A waterspout is a tornado that forms over a body of water, or a tornado that moves from land onto water

5. Tornado Facts Tornadoes can occur almost anywhere in the world
Duration: a few minutes
Diameter (Avg.): 0.4 km
Length of path (Avg.): 6 km
Funnel can travel from 0 mph up to ~70 mph, usually travels at 30 mph
99% of all tornadoes in Northern Hemisphere rotate counterclockwise
Texas is #1 for frequency of tornadoes per year
Between 1950 and 1995 Texas had 5,722 recorded tornadoes
Risk of death in a tornado in Texas: 1 in 1,054,267

6. How do tornadoes form?
Winds at 2 different altitudes blow at 2 different speeds creating “wind shear”
(Creates an invisible, horizontal spinning effect in the lower atmosphere)

7. Wind Shear

8. How do tornadoes form?
Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.

9. How do tornadoes form?
An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

11. Beginning Stage: Tornado begins as a rotating wall cloud which quickly evolves into a funnel

12. Early Stage:
Tornado funnel develops (may be transparent) and extends down from the cloud to the ground

13. Mature Stage: Tornado funnel reaches maximum width as well as maximum intensity then begins to shrink

14. Decay Stage:
Tornado may remain stationary and take on a ropelike appearance before dissipating

15. Tornado Wind Speed
In 1971, Dr. Fujita developed a way of measuring the winds of a tornado. He reasoned that there was a link between wind speed and the damage caused by a tornado. There are 6 categories of tornados
(F0 – F5)
*** IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place -- even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.

16. Fujita vs Enhanced Fujita
*** IMPORTANT NOTE ABOUT ENHANCED F-SCALE WINDS: The Enhanced F-scale still is a set of wind estimates (not measurements) based on damage. Its uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to the 28 indicators listed below. These estimates vary with height and exposure. Important: The 3 second gust is not the same wind as in standard surface observations. Standard measurements are taken by weather stations in open exposures, using a directly measured, "one minute mile" speed.

19. Weak Tornadoes 69% of all tornadoes Less than 5% of tornado deaths
Lifetime minutes
Winds less than 110 mph

20. F0 Category (Weak) winds (40-72) mph , little damage
Damage: tree branches snapped, chimneys toppled, signs torn down

21. Strong Tornadoes 29% of all tornadoes Nearly 30% of all tornado deaths
May last 20 minutes or longer
Winds mph

22. F3 Category (Strong) winds: (158-206) mph, severe damage
Damage: most trees uprooted, trains overturned, roofs torn off, walls demolished

23. Violent Tornadoes Only 2% of all tornadoes 70% of all tornado deaths
Lifetime can exceed 1 hour

24. F5 Category (Violent) winds: (261- 319) mph, incredible damage; rare
Damage: bark peeled off trees, houses lifted off foundations, vehicles travel greater than 100 m through the air

25. Tornado Occurrence by Category

26. Tornado Deaths by Category

27. Tornado Indicators Greenish colored sky Mammatus clouds
Sudden drop in barometric pressure
Large hail of at least .75 in. diameter
Strong winds > 60 mph
Frequent and intense lightning
Rotating wall cloud or a cloud that appears to hang from the sky
A loud rumbling noise- seek shelter!

28. Mammatus clouds
Green sky

29. Tornado Frequency Southern states: peak March - May,
Northern states: Summer.
Time of day: peak 3 and 9 p.m

30. “Tornado Alley” covers the Great Plains states
Where Tornados Occur
“Tornado Alley” covers the Great Plains states

31. Did Dorothy from the Wizard of Oz live in “Tornado Alley?”

36. Dopplar Radar
Uses radio waves to measure intensity of precipitation and how fast the rain or hail is moving toward or away from the radar

37. Doppler image of a rain-wrapped tornado
Tornados on Radar
Doppler image of a rain-wrapped tornado

38. Tornado Watches & Warnings
Watch - conditions are favorable for severe weather to develop
Warning - information provided by weather radar, and spotters (law enforcement) on the ground, severe weather is imminent.
Severe thunderstorm warnings are passed to local radio and television stations and are broadcast over local NOAA Weather Radio stations serving the warned areas. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities.

39. What to do…
If a Warning is issued or if threatening weather approaches:
In a home or building, move to a pre-designated shelter, such as a basement.
If an underground shelter is not available, move to an interior room or hallway on the lowest floor and get under a sturdy piece of furniture.
Stay away from windows.
Get out of automobiles.
Do not try to outrun a tornado in your car; instead, leave it immediately.
Mobile homes, even if tied down, offer little protection from tornadoes and should be abandoned.

40. Tornado History
“Tri-State Tornado” - the most violent tornado on record
March 18, 1925, the tornado formed in Missouri and traveled 219 miles across Illinois into Indiana
The funnel was up to ¾ of a mile across and traveled as fast as 73 mph.
It killed approximately 635 people

41. Tornado Myths
A highway overpass is a safe place to take shelter under during a tornado
Opening windows during a tornado will help balance the pressure between the inside and outside of the house and may prevent destruction of the structure
One should seek shelter in the southwest corner of a house or basement.

42. Tornado Oddities
Tornados are reported to routinely carry objects many miles and have:
sucked the frogs out of a pond and dropped them on a town
carried a necktie rack with 10 ties attached 40 miles
carried a flour sack 110 miles from a mill
Tornados also drive objects into other objects and have:
Driven splinters into an iron fire hydrant
Driven straw and grass into telephone poles

43. View from the air of a tornado path in central OK