Transcript Tornadoes
Chapter 14 Oldest Known Photograph of a Tornado (1884) Tornadoes Rapidly rotating column of air that flows around a small area of intense low pressure with a circulation that reaches the ground. Tornadoes Table 14-2, p. 400 Tornadoes When F-Scale Converted to EF-Scale Enhanced Fujita Scale Feb 1 2007 F Scale Wind Speed EF-Scale Wind Speed F0 45-78 EF0 65-85 F1 79-117 EF1 86-109 F2 118-161 EF2 110-137 F3 162-209 EF3 138-167 F4 210-261 EF4 168-199 F5 262-317 EF5 200-234 Wind speeds in mph, 3-second gust Objectives: 3, EF-Scale structure; 4, EF vs F-Scale DOD to Wind Speed to EF-Scale EF-Scale Categories Wind Speed Ranges EF0 65-85 EF1 EF2 86-110 111-135 EF3 136-165 EF4 166-200 EF5 >200 Wind speeds in mph, 3-second gust Objectives: 3, EF-Scale structure Why the EF-Scale was created Need more damage indicators recalibrate winds associated with F-scale ratings better correlate wind and rating account for construction variability Flexibility, Extensibility, Expandability The framed house is one of only a few F-scale damage indicators. Evidence indicates a well constructed house can be blown away by winds much less than 260 mph (Phan and Simiu,2003). Tornadoes Tornado outbreaks Families, super outbreak Super tornado outbreak April 3-4, 1974 315 deaths http://www.april31974.com/ Palm Sunday April 11 1965 47 Tornadoes in 12 hours span 271 deaths, 3400 people injured 1.1 billion damage (2003 $$$$) May 3-4 1999 Oklahoma City 66 tornadoes 46 fatalities, 800 injured 1.5 billion damage An F-5 tornado http://www.norman.noaa.gov/2000/05/first-anniversary-of-may-3-1999tornado-outbreak-highlights-importance-of-warnings/ Fig. 14-37, p. 396 Tornadoes Tornado Occurrence US experiences most tornadoes Tornado Alley (warm, humid surface; cold dry air aloft) Highest occurrence spring (may June), lowest winter Highest Death Toll , April Where else do tornadoes form? Two of the highest concentrations of tornadoes outside the U.S. are Argentina and Bangladesh. Both have similar topography with Brazil (Argentina) or from the Indian Ocean (Bangladesh). mountains helping catch low-level moisture from over Brazil (Argentina) or from the Indian Ocean (Bangladesh). Palm Sunday Tornado April 11 , 1965 271 deaths http://www.crh.noaa.gov/dtx/palmsunday/ Super tornado outbreak April 3-4, 1974 http://www.april31974.com/ 315 deaths http://www.tornadoproject.com/toptens/toptens.htm Radar Doppler Radar Phased array radars http://www.oar.noaa.gov/spotlite/2008/spot_radar.html Tornadoes Tornado winds Measurement based upon damage after storm or Doppler radar For southwest approaching storms, winds strongest in the northeast of the storm, 220 kts maximum Multi-vortex tornados Tornadic Formation Basic requirements are: an intense thunderstorm Vertical wind shear Cold air aloft and warm moist air near surface (unstable conditions) Initiation of convection Capping inversion Vertical wind shear Cold air aloft and warm moist air near surface (unstable conditions) Initiation of convection Capping inversion Tornadoes Seeking shelter Basement or small, interior room on ground floor Indoor vs. outdoor pressure The Fujita Scale Based upon the damage created by a storm F0 weakest, F5 strongest Enhanced Fujita Scale Severe Weather and Doppler Radar Doppler radar measures the speed of precipitation toward and away radar unit Two Doppler radars can provide a 3D view TVS, Doppler lidar NEXRAD Waterspouts Rotating column of air that is connected to a cumuliform cloud over a large body of water Tornadic waterspout