Natural Hazards and Disasters Chapter 15 Thunderstorms and Tornadoes

1. Natural Hazards and Disasters Chapter 15 Thunderstorms and Tornadoes

2. Twister Demolishes Kansas Town • Small town of Greensburg, Kansas was effectively wiped off map by powerful EF-5 tornado, May 4, 2007 • First “5” on the new Enhanced Fujita Scale (EFS) • National Weather Service provided 30 minutes of warning that major tornado was headed for Greensburg, activated emergency sirens and emergency message 10-15 minutes before tornado struck • 2.7-km-wide tornado decimated town in 15-20 minutes, with winds estimated at 320-335 km/hr • Nine people were killed in Greensburg, and most buildings in center of town were destroyed

5. Thunderstorms Most common in latitudes near equator Form as unstable, warm and moist air rapidly rises into colder air and condenses, releasing heat and causing updraft Water droplets freeze in anvil-shaped cumulonimbus clouds Cold air pushing under warm air along cold front is common triggering mechanism Thunderstorm systems can travel for more than 1,000 km Lightning strikes kill people Strong winds down trees, power lines and buildings Cause numerous wildfires, hail and tornadoes

6. Lightning Results from strong separation of charge that builds up between top and bottom of cumulonimbus cloud Charge separation increases as water droplets and ice particles are carried in droplets and collide with downward-moving ice particles or hail Top of cloud carries strong positive charge Bottom of cloud carries strong negative charge Negative charges near bottom of clouds attract positive charges toward ground surface, especially to tall objects Eventually, electrical resistance in air cannot keep opposite charges apart

7. Lightning Negatively charged step leaders angle their way toward ground Leaders fork as they find different paths to ground Positive leaders reach upward toward them from elevated objects on ground When one of pairs of leaders connects, massive negative charge follows conductive path of leader stroke from cloud to ground Followed by return stroke moving back toward cloud along established connection Instantly heats air to temperatures about 28,000oC Accompanying expansion of air at supersonic speed is thunder

8. Downbursts Discovered by Dr. T. Fujita Small areas of rapidly descending air can develop in strong thunderstorms As fast as 200 km/hr Accompanied by descending mass of cold air, sometimes rain Cause wind shear, which can cause planes to plummet to ground as they lose lift from under wings Damage sometimes mistaken for tornado, but evidence will show straight-line winds, rather than rotational damage from tornadoes

9. Hail Causes $2.9 billion in annual damages to cars, roofs, crops and livestock Hailstones appear when warm and humid air in thunderstorm rises rapidly into upper atmosphere and freezes Upward and downward movement accumulates layers of ice until heavy enough to overcome updrafts and fall to ground Largest hailstones can be larger than baseball Hailstorms are most common in northern plains, least common in coastal areas

10. Safety During Thunderstorms Immediate cause of death in lightning strike is heart attack Residual effects to survivors are deep burns, damage to nerves, brain, vision and hearing Maximum number of deaths on Sunday around 4 p.m., presumably because more people are outside

11. Safety During Thunderstorms • Observe following precautions during thunderstorms: • Take cover if you hear thunder within 30 seconds of lightning and stay there until no lightning for at least 30 minutes • Take cover in enclosed building (not picnic shelter) • Do not touch anything that is plugged in • Do not use phone with cord (cordless phones and cell phones are okay) • Do not take a shower or bath or wash dishes • Stay away from high places or open fields or open water

12. Safety During Thunderstorms • Observe following precautions during thunderstorms: • Stay away from tall trees, power poles or other tall objects • If you are trapped in the open, your skin tingles or your hair stands on end, you are in danger of being struck • Crouch on balls of feet with heels touching • Do not lie down or increase contact with ground (ground conducts electricity) • Stay away from metal objects • Stay inside car with windows rolled up, do not touch any metal

13. Seconds away from being struck…

14. The Study of Tornadoes 77 A.D.: Pliny the Elder’s Naturalis Historia 1571: Florentine Codex, tornadoes in Aztec cities 1643: MA Governor John Winthrop writes the first known tornado report in North America 1700’s: Benjamin Franklin speculates about the nature of water spouts 1847: Physicist Joseph Henry initiates a Smithsonian-backed project to catalog tornado observations

15. The Study of Tornadoes • 1870: President Grant authorizes a storm forecasting program • 1884-86: John Park Finley, U.S. Army Signal Corps, collects and analyzes data with the intent of predicting severe storms and tornadoes • Fairly successful with thunderstorms, less so with tornadoes • Use of the word tornadonot allowed to appear in forecasts • 1891: Weather Bureau placed under the control of the U.S. Department of Agriculture • Continued collecting data, but downplayed the need for prediction • First State Climatologist of Iowa, Gustavus Hinricks, states that tornadoes do not occur in Iowa during the summer

16. The Study of Tornadoes • 1940s: Experimental tornado warning systems installed in Wichita, Kansas City and St. Louis • 1950s: Dr. T. Fujita begins study at the University of Chicago • Fujita Scale, downbursts, hook echo, 70-year U.S. climatology of tornadoes, satellite imagery of cloud movement • 1960s: Supercells identified as “prolific tornado producers” • 1970s: “The Golden Age” of tornado research • Nationwide Doppler program established (JDOP) • Fujita Scale introduced • 1974 Super Outbreak, 148 tornadoes, 13 states, 2 days • 1980s-90s • Continued improvements in computer modeling and forecasting • Better identification of tornadic signatures within supercells

17. The Study of Tornadoes The CASA Array • 1990s: NEXRAD deployed • 158 high-resolution Doppler radars • Today: More advanced and sophisticated detection and modeling • Average lead time of 15 minutes before a tornado is reported • Baron Tornado Index • The “Hallgren Wall” • Dual-polarization radar • Phased-array • Distributive Collaborative Adaptive Sensing

18. Tornadoes Narrow funnel of intense wind, usually with counterclockwise rotation (1% rotate clockwise) Mesocyclone (rotating cylindrical wind within anvil-shaped thundercloud) sinks below flat could base to form wall cloud Rotation accelerates and tightens to form tornado, which descends to ground often after heaviest rain and hail have passed Nature’s most violent storms, most significant natural hazard in midwestern U.S. Often form in right-forward quadrant of hurricanes, where wind shear is strongest

19. Tornadoes

20. Tornadoes Storms that lead to tornadoes form from collision of warm, humid air from Gulf of Mexico and cold air from Canada – no barrier in central U.S. to keep air masses apart Number of tornadoes is greatest in Tornado Alley: parts of Texas, Oklahoma, Arkansas, Missouri, Kansas

21. Tornadoes in the U.S. 1950-2010 Annually • 1,294 tornadoes • 2001-2010 • 58 fatalities • 2000-2009 • $1.1 billion damaged • 1990-2007

22. Tornadoes • Tornado outbreak is series of tornadoes spawned by group of storms • Outbreaks have killed as many as several hundred people in as many as 13 states • Eight storms produced 58 tornadoes in central Oklahoma in May 1999, killing 59 people • Superoutbreak of 1974 produced 148 tornadoes over 17 hours along 4,180 km, killing 315 people • Most tornadoes stay on ground less than 30 minutes, track to northeast • Ground speeds range from 50 to 80 km/hr • Internal wind speeds can be as high as 515 km/hr • Deadliest tornado ever? • Bangladesh, 26 April 1989, 1,300 dead

24. Tornadoes ??? There is uncertainty as whether or not the Tri-State was one tornado or a family

27. Tornado Development • Derive energy from latent heat released when water vapor condenses • Latent heat creates instability in atmosphere • Generally form when there is shear in wind directions • Surface winds from southeast • Winds from west higher in atmosphere • Shear creates roll of horizontal currents • Roll can be dragged into vertical rotation axis by updraft in thunderstorm to form rotation cell • Cell sags to form wall cloud – most obvious danger sign for imminent formation of tornado • Smaller funnel clouds form within wall cloud, descend to ground to become tornadoes • Mammatus clouds are second warning sign

28. Tornado Development

29. Tornado Development Generally form toward trailing end of thunderstorm, sometimes after worst of storm seems to have passed May hear approach as hissing sound to strong roar, like oncoming freight train Favorable conditions for formation are collision of two fronts in strong low-pressure center, recognizable as hook echo As tornado matures, it becomes wider and more intense In waning stages, it becomes narrow, sometimes ropelike before breaking up

30. Tornado Development

31. Tornado Development

32. Tornado Development National Weather Service’s Severe Storms Forecast Center uses Doppler radar, wind profilers and automated surface observing systems to predict and identify tornadoes When thunderstorms seem capable of producing tornadoes: issue tornado watch When Doppler radar shows strong indication of vorticity or rotation, or when tornado is sighted: issue tornado warning

33. Tornado Damages Ted Fujita’s observations of tornado damages showed swaths of severe damage adjacent to areas of only minor damage Swaths of debris were left in curved paths Hypothesized that smaller vortices with most intense winds rotate around tornado Vortices have since been photographed

34. Tornado Damages Vortices on a Vortex

35. Tornado Damages • Damage to home usually begins with loss of roofing material, followed by glass breakage • Roof lifts off • Exterior walls collapse, then interior walls • Small interior rooms, halls, and closets fail last • Hurricane straps connect horizontal and vertical parts • Most susceptible to damage: • Farm outbuildings • Mobile homes • Apartment and condo buildings • Family homes • High-rise office buildings and hotels

36. Tornado Damages Many people believe that low pressure in tornado vacuums up objects, causes buildings to explode Experts believe extreme winds and flying debris cause almost all destruction Debris sprays outward from base of tornado

37. Fujita Tornado Scale • Fujita scale devised to classify severity of tornadoes based on internal wind speeds and damage produced • F0 causes minimal damage • F5 blows away strong frame homes • F-scale damage chart and photographs correspond to wind speeds • Enhanced Fujita (EF) scale is based on detailed wind measurements and long-term records of damage, uses three-second wind gust estimates at site, more reliable than old scale • Shows that particular damages occur at much lower wind speeds

38. Fujita Tornado Scale

39. Fujita Tornado Scale

40. Fujita Tornado Scale

41. Fujita Tornado Scale

42. Safety During Tornadoes Seek shelter underground or in specially constructed shelters Otherwise, interior space with strong walls and ceiling, away from windows Main danger is from flying debris Mobile homes and cars are not safe If outside, lie in a ditch and cover your head May be able to drive to safety at right angles to tornado’s path

43. Safety During Tornadoes Move to tornado shelter, basement, interior room without windows If location is vulnerable, protect head from flying debris Highway overpass is not good location – acts as wind tunnel, creates traffic jam Cars can provide some protection below window line

45. April 2011 Outbreaks • April 14-16: 155 Confirmed Tornadoes, 43 Fatalities • April 25-28: 426 Tornadoes Reported, 146 Confirmed, 339 Fatalities* as of 3:00 P.M., CDT, 1 May 2011 (292 on 27 April)** **Currently the highest outbreak total in U.S. history, second: the Deep South Outbreak (332, 21-22 March 1932) *Currently the third highest total in a single day in U.S. history, behind the Tri-State tornado (695, 18 March 1925) and the Natchez, MS , tornado (317, 6 May 1840) (The Tri-State tornado was not an outbreak, it was a single tornado, which currently holds the record for path length at 219 miles - the Tuscaloosa/Birmingham track may break that record, with a preliminary estimate of 280 miles) April 25-28

50. Case In Point Tornado Safety: Jarrell Tornado, Texas, 1997 Tornado watch issued at 1 p.m., tornado warning issued at 3:25 p.m. Tornado watchers spotted funnel and sounded alarm F5 tornado wiped 50 homes off foundations Golf-ball-size hail and torrential rain pounded area Wind speeds were 400-435 km/hr for 20-25 minutes At least 30 people died