Tornadoes

1. Tornadoes Nature’s Most Violent Storms

2. Bellringer • Have a seat and take out something to write with!

3. Video • http://www.youtube.com/watch?v=vG2DTAzZAzw • 2011 Joplin Tornado

4. Bellringer • Which do you think is more destructive, an average hurricane or an average tornado?

5. Objectives • Go over reaction to yesterday’s video • Notes on tornadoes

6. Video Questions • Why shouldn’t people try to chase tornadoes? • Describe the damage caused by the tornado.

7. Tornados • Tornadoes occur all over the world, but are most common in the US east of the Rocky Mountains during the spring and summer months • On average 800 tornadoes are reported nationwide resulting in 80 deaths and over 1,500 injuries

8. Tornadoes • A tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground. • The most powerful tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more. • Damage paths can be more than 1 mile wide and 50 miles long.

9. Thunderstorms • Tornadoes form from thunderstorms • Thunderstorms result from the lifting of unstable, moist, warm air mass • Latent Heat (hidden heat) is released in the formation of clouds, by the condensation of water, and by the freezing of hail. • This extra heat energy creates additional lifting of the air mass

10. How Tornadoes Form • Starts as an invisible horizontal spinning air mass in the lower atmosphere. This is caused by changing wind direction, increase in wind speed and height.

11. How Tornadoes Form • The rising air in the thunderstorm super-cell tilts the rotating air from horizontal to vertical

12. How 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.

13. How Tornadoes Form • A lower cloud base in the center of the photograph identifies an area of rotation known as a rotating wall cloud. This area is often nearly rain-free.

14. How Tornadoes Form • Moments later a strong tornadoes develops in this area. Softball-size hail and damaging “straight-line” winds also occurred with this storm.

18. Tornado Ally, USA • Tornado Ally stretches from Texas to the Dakotas • It is where most of the tornadoes in the United States occur • Tornadoes form there from moist air from the Gulf, hot dry air from the southwest, and cool dry air from the upper plains colliding • These different air masses create wind shear which create that horizontal rotating air mass

20. Tornado Variations • Tornadoes may appear nearly transparent until dust and debris are picked up • Occasionally, two or more tornadoes may occur at the same time • Waterspouts are weak tornadoes that form over warm water • Water spouts occasionally move inland becoming tornadoes causing damage and injuries

23. Weak Tornadoes • 69% of all tornadoes • Less than 5% of tornado deaths • Lifetime 1-10+ minutes • Winds less than 110 mph

24. Strong Tornadoes • 29% of all tornadoes • Nearly 30% of all tornado deaths • May last 20 minutes or longer • Winds 110-205 mph

25. Violent Tornadoes • Only 2% of all tornadoes • 70% of all tornado deaths • Lifetime can exceed 1 hour • Winds greater than 205 mph

26. Checkpoint • What conditions form tornadoes?

27. Tornadoes Occur Anywhere • Carolinas Outbreak: • March 28, 1984 afternoon-evening • 22 tornadoes • 57 deaths • 1,248 injuries • $200 million dollars in damage

28. Pennsylvania-Ohio Outbreak • May 31, 1985 late afternoon-evening • 41 tornadoes • 75 deaths • 1,025 injuries • $450 million dollars in damage

29. Plains Outbreak • April 26-27, 1991, afternoon of 26th through early morning 27th • 54 tornadoes • 21 deaths • 308 injuries • $280 million dollars in damage

30. Frequency of Tornadoes • Tornadoes can occur at any time of the year • Tornadoes are most likely to occur between 3 and 9 pm • The average tornado moves from southwest to northeast • The average forward speed is 30 mph, but may vary from nearly stationary to 70 mph • The total number of tornadoes is probably higher than we think, because not everyone is reported or seen by people

33. Tornado Myths • Highway overpasses are a safe place to shelter if you are on the road when you see a tornado coming. • Opening windows to equalize air pressure will save a roof, or even a home, from destruction by a tornado. • Tornadoes never strike big cities. • Some towns are “protected” • The southwest corner of a basement is the safest location during passage of a tornado

34. Checkpoint • Why has the number of tornadoes in the US increased over time?

35. Scale and dangers • Unlike hurricanes tornadoes are rated on the damage they inflict on human-built structures and vegetation instead of their maximum sustained wind speeds. • The scale they are measured on in called “The Fujita Scale”

36. The Fujita Scale • Scale ranges from F0 to F5 • It is very possible that there are thousands of more F0 and F1 tornadoes each year that just are never seen by people.

37. Frequency vs Death

38. The Fujita Scale • Also known as the Fujita-Pearson Scale • It may not be a perfect system for linking damage to wind speed, but it had distinct advantages over what had gone on before inception. • It is also simple enough to use in daily practice without involving much additional expenditure of time and money.

39. The Fujita Scale • F0 (Gale Tornado): 40-72mph • Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.

40. The Fujita Scale • F1 (Moderate Tornado) 73-112mph • The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.

41. The Fujita Scale • F2 (Significant Tornado) 113-157 mph • Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushes over; large trees snapped or uprooted; light objects missiles generated.

42. The Fujita Scale • F3 (Severe Tornado) 158-206 mph • Roof and some walls torn off well constructed houses; trains overturned; most trees uprooted.

43. The Fujita Scale • F4 (Incredible Tornado) 261-318 mph • Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters (football field); trees debarked; steel reinforced concrete structures badly damaged.

44. The Fujita Scale • F6 (Inconceivable Tornado) 319-379 mph • These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess produced by the F4 and F5 winds that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever achieved, evidence for it might only be found in some manner of ground swirl patterns.

45. Important to note • The size of a tornado is not necessarily an indication of its intensity Large tornadoes can be weak, and small tornadoes can be violent. • Tornadoes go through a life cycle and their size varies during it. • The official estimated scale of the tornado is made after the tornado has passed so the total damage can be assessed.

46. What they look for to rate a tornado • The attachment of the walls and floor to the foundation of the building • The attachment of the roof to the rafters and walls • Whether or not there are steel reinforcing rods in concrete or cinder block walls • Whether there is mortar between the cinder blocks

47. Subjectivity of the Fujita Scale • The Fujita Scale is very subjective, and varies according to how experienced the surveyor is. • Insurance companies have their own “experienced” surveyors because they don’t always trust the experts, scientists, and engineers • Media hype also tends to over estimate the Fujita Scale ratings of tornadoes.

48. “The Seymour” - Texas • Would have destroyed a town. • Only produced telephone pole and tree damage. • F2

49. Checkpoint • What is the Fujita Scale based on? • Do large tornadoes always produce the most damage? • Why doesn’t Pearson get as much credit as Fujita?

50. The 1925 Tri-State Tornado • Started on March 18, 1925 • Tore through Southeast Missouri, Southern Illinois, and Southwest Indiana.