CHAPTER 12 TORNADOES

1. CHAPTER 12 TORNADOES

2. Tornadoes • Some supercells create enough rotation that the circulation will contract and reach the ground – a tornado • Defined as a violently rotating column of air, in contact with the ground, and below a cumuliform cloud Significant tornado days per century Tornado days per year

3. Tornadicsupercell in Panhandle

4. Fig. 12.1, p. 334

5. Distribution • Tornado “days”

6. Fig. 12.4, p. 337

7. Seasonal Shift NSSL Animation: Tornado probability climatology http://www.nssl.noaa.gov/hazard/tanim8094/sigtanim2195.html http://www.nssl.noaa.gov/hazard/tanim8094/viotanim2195.html

8. Fig. 12.6, p. 338

9. Fig. 12.7, p. 338

10. Tornado Trivia • Funnel Cloud until circulation reaches ground • Shapes • Mostly < 135 mph, but can exceed 250 mph • Diameters: • Most: 300 to 2000 ft • Small as 20 feet, big as 1+ mi! • Mostly CCW (because most tornadicsupercells rotate CCW) • Cyclostrophic balance, HPGF and Centrifugal • Mostly move SW to NE, 25 to 50 mph • Can last a few mintues, or hours (long track, tornado “family”)

11. Fig. 12.2, p. 335

12. Tornadoes • Non-supercelltornadoes also occur – they often form along boundaries in unstable environments, e.g. a squall line MCS. (like bookend vortex of a bow echo).: landspouts & waterspouts Before a tornado forms, a low cloud called the “wall cloud” will appear from under the main updraft and mesocyclone

13. TORNADO LIFE CYCLE • Dust-whirl stage • Mature stage • Shrinking • Decay stage • NWS Jetstream

14. Fig. 12.3, p. 336

15. Wedge tornado • Windsor, CO

16. Favorable conditions for tornadoes Example from book • In addition to moisture, instability, and lifting, we need strong wind shear • At low levels, southerly winds bringing warm, moist air into the area • Aloft, advection of dry air adds to instability • Upper-level divergence leads to low-level upward motion

17. A “textbook” example Surface map

18. A “textbook” example

19. Supercells!

20. Severe weather reports

21. Asymmetric Winds Fig. 12.9, p. 340

22. Fig. 12.10, p. 340

23. Fig. 12.11, p. 341

24. Monitoring severe weather 1-3 days in advance – convective outlook A few hours in advance – severe thunderstorm or tornado watch – this means conditions are favorable – keep alert www.spc.noaa.gov

25. Monitoring severe weather Warnings: Issued for one or more counties when a severe thunderstorm or tornado has been spotted or observed by radar

26. Tornado warning

27. Seeking shelter • Basement or small, interior room on ground floor • Do NOT open windows • Mobile Home: Must leave. Period. • Auto: See previous slide • NEVER under an overpass

28. Current Events: Mapleton, IA • http://vimeo.com/22221449 • Radar • Radar (Velocity) • Satellite • 032 WFUS53 KOAX 100008 TOROAX IAC133-100045- /O.NEW.KOAX.TO.W.0010.110410T0008Z-110410T0045Z/ BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA 708 PM CDT SAT APR 9 2011 THE NATIONAL WEATHER SERVICE IN OMAHA HAS ISSUED A • * TORNADO WARNING FOR... NORTHEASTERN MONONA COUNTY IN WEST CENTRAL IOWA... • * UNTIL 745 PM CDT * AT 707 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO. THIS DANGEROUS STORM WAS LOCATED 11 MILES EAST OF WHITING...OR 34 MILES SOUTHEAST OF SIOUX CITY...AND MOVING EAST AT 25 MPH. • * LOCATIONS IMPACTED INCLUDE... MAPLETON. • PRECAUTIONARY/PREPAREDNESS ACTIONS... THIS TORNADO WARNING REPLACES THE SEVERE THUNDERSTORM WARNING THAT WAS IN EFFECT FOR THE SAME AREA. GO TO A BASEMENT OR SMALL INTERIOR ROOM ON THE LOWEST FLOOR! TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT YOURSELF FROM FLYING DEBRIS. &&\ • Newspaper • SPC

32. Enhanced Fujita scale for tornado intensity • Based on damage – rating is assessed after the tornado (different from hurricanes, when the category is assigned while the storm is happening) • Originally developed by Dr. Ted Fujita of the University of Chicago in the 1970s • Updated in 2007 to the “Enhanced Fujita” scale • EF4 and EF5 tornadoes are very rare, but most deaths are caused by them

33. Fig. 12.12, p. 344

35. First EF5 (new scale) • Greensburg, KS, May 4, 2007

36. TORNADO OUTBREAKS • Outbreak: Typically, conditions will be favorable over a large area for supercells, and we may have many tornadoes for a synoptic event. • Tornado Families • Single supercell, multiple tornado “drops” • Typical pattern: • Super outbreak

37. Table 12.4, p. 345

38. Table 12.5, p. 346

39. New Outbreaks for the record books • Super Outbreak, 27 April 2011 • http://www.srh.noaa.gov/bmx/?n=event_04272011 • http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1796 • Joplin EF-5, 22 May 2011, ~160 Fatalities • http://www.crh.noaa.gov/sgf/?n=event_2011may22_summary

40. Fig. 12.15, p. 346

41. Fig. 12.15, p. 346

42. Fig. 12.16, p. 347

43. NWS Photo Fig. 12.17, p. 347

44. TORNADO FORMATION • Basic requirements are the usual for a thunderstorm (M , L, I ), and strong vertical wind shear. • Supercell Tornadoes • Wind sheer causes spinning vortex tube that is pulled into thunderstorm by the updraft • Terms: Mesocyclone, BWER, rear flank downdraft, vertical stretching, funnel cloud, rotating cloud, wall cloud, RFD, FFD

45. Fig. 12.18, p. 348

46. Fig. 12.20, p. 349

47. Fig. 12.19, p. 348

48. TORNADO FORMATION • Nonsupercell Tornadoes • Boundaries give rise to low level rotation • Convection stretches rotation • Also bookends of bow echoes • Remember the Florida bow echoes?

49. Fig. 12.24, p. 353

50. Fig. 12.23, p. 352