CHAPTER 12 TORNADOES
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Transcript of CHAPTER 12 TORNADOES
CHAPTER 12
TORNADOES
CHAPTER 12
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
Tornado days per yearSignificant tornado days per century
Fig. 12.1, p. 334
Tornado “days”
Fig. 12.4, p. 337
NSSL Animation: Tornado probability climatologyhttp://www.nssl.noaa.gov/hazard/tanim8094/sigtanim2195.html
http://www.nssl.noaa.gov/hazard/tanim8094/viotanim2195.html
Fig. 12.6, p. 338
Fig. 12.7, p. 338
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 tornadic supercells 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”)
Fig. 12.2, p. 335
Non-supercell tornadoes 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 Before a tornado forms, a low cloud called the “wall cloud” will appear from under the main updraft and mesocyclone from under the main updraft and mesocyclone
• Dust-whirl stage
• Mature stage• Shrinking• Decay stage• NWS
Jetstream
Fig. 12.3, p. 336
Wedge tornado
Windsor, CO
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
Example from bookExample from book
Surface map
Fig. 12.9, p. 340
Asymmetric Winds
Fig. 12.10, p. 340
Fig. 12.11, p. 341
1-3 days in advance – convective 1-3 days in advance – convective outlookoutlook
A few hours in advance – severe A few hours in advance – severe thunderstorm or tornado watch – this thunderstorm or tornado watch – this means conditions are favorable – keep means conditions are favorable – keep alertalert
www.spc.noaa.govwww.spc.noaa.gov
Warnings:Warnings:Issued for one or more counties when Issued for one or more counties when a severe thunderstorm or tornado has a severe thunderstorm or tornado has been spotted or observed by radar been spotted or observed by radar
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
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
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
Fig. 12.12, p. 344
Greensburg, KS, May 4, 2007
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
Table 12.4, p. 345
Table 12.5, p. 346
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
Fig. 12.15, p. 346
Fig. 12.15, p. 346
Fig. 12.16, p. 347
Fig. 12.17, p. 347
NWS Photo
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
Fig. 12.18, p. 348
Fig. 12.20, p. 349
Fig. 12.19, p. 348
Nonsupercell Tornadoes◦ Boundaries give rise to low level rotation◦ Convection stretches rotation◦ Also bookends of bow echoes
Remember the Florida bow echoes?
Fig. 12.24, p. 353
Fig. 12.23, p. 352
Doppler radar measures the speed of precipitation toward and away radar unit
Two Doppler radars can provide a 3D view Couplet and TVS (Tornado Vortex Signature) NEXRAD is the national Doppler system
◦ Due for an upgrade which will be able to tell hail from drops better
NWS Photo
Fig. 12.26, p. 354
Rotating column of air that is connected to a cumuliform cloud over a large body of water
Tornadic waterspout vs. fair weather Dust Devils are cousins, same balance
◦ Cyclostrophic
Fig. 12.28, p. 356