1. Tornadoes: Terminology  Tornado: a violently rotating column of air in contact with the ground. Also called “twister” and “cyclone”  Waterspout: a tornado over water, generally much weaker than a tornado  Funnel Cloud: a rapidly rotating column of air not in contact with the ground, often the precursor to a tornado, extending from the base of a cumulonimbus cloud

2. Tornado Safety  Avoid blowing debris (don’t become a part of it, either) –Get underground, if possible (wind speed = 0) –Find a ditch or low spot and cover your head –Interior, windowless room of a sturdy building, preferably under something that won’t fall on you but will protect you from falling/flying debris –Avoid cars and mobile homes, highway overpasses

3. Tornado Intensity  The Fujita Scale: based upon damage surveys and not direct measurement of winds –Similar to Saffir-Simpson scale for hurricanes –Ranges from F0 (EF0) for very weak tornadoes to F5 (EF5) for incredibly strong tornadoes –Scale goes higher (F12) but it’s unlikely we’ll see anything stronger than an F5- how can damage be any worse than “incredible?” –The strongest tornadoes develop within supercells –Enhanced Fujita Scale Enhanced Fujita ScaleEnhanced Fujita Scale

5. Supercell Thunderstorms  Produce the most extreme severe weather –Large, strong tornadoes  Wind shear- direction, speed  Rotating thunderstorms –Long (~6 hour) lifespan  Wind shear- direction, speed  Tilted updraft –Large hail and damaging winds Large hail Large hail  Extreme instability  Extremely strong updrafts and downdrafts

6. Supercells: Extreme Vertical Motion  The Lid (capping inversion) –Warm, dry air overlies warm, moist air –Result of low-level S,SE winds from Gulf of Mexico and SW winds above this layer blowing from the Mexican plateau –Limits development of “wimpy” thunderstorms: more energy available for a few supercells versus lots of run-of-the-mill thunderstorms

7. Supercells: Extreme Vertical Motion –Breaking the Lid  Daytime heating weakens it  Rising air will cause a more rapid cooling aloft than near surface: result is explosive thunderstorm development

8. Supercells: Long-Lived Monsters  Directional and speed shear tilts the updraft  Separates inflow and outflow –Constant supply of warm, moist air

9. Supercells: Tornado Development  Directional shear induces thunderstorm rotation  Speed shear creates horizontal roll  Roll tilts vertically in updraft

10. Supercells: Tornado Development  Strong updrafts and downdrafts, especially the rear flank downdraft, appear to be important in tornadogenesis –From Markowski et al, 2002, Direct Surface Thermodynamic Observations within the Rear-Flank Downdrafts of Nontornadic and Tornadic Supercells, Monthly Weather Review

13. Tornadoes  Suction Vortices: think of them as mini tornadoes within the primary funnel Image from www.atmo.arizona.edu/.../apr2609.jpg Image from www.atmo.arizona.edu/.../apr2609.jpg  Are tornadoes becoming more frequent?

14. Key Figures  Tables 14.8, 14.9, 15.8, 15.10, 15.12  Interesting Time-Lapse Movie of Thunderstorm Development Interesting Time-Lapse Movie of Thunderstorm Development Interesting Time-Lapse Movie of Thunderstorm Development  Time-Lapse 2 / Time-Lapse 3 Time-Lapse 2Time-Lapse 3 Time-Lapse 2Time-Lapse 3  Multi-Vortex Tornado Multi-Vortex Tornado Multi-Vortex Tornado  M-V Tornado from Helicopter M-V Tornado from Helicopter M-V Tornado from Helicopter  Rotating Supercells in Wyoming/Texas Rotating Supercells in WyomingTexas Rotating Supercells in WyomingTexas  What you normally should NOT do What you normally should NOT do What you normally should NOT do