Tornadoes: TerminologyTornadoes: Terminology Tornado: a violently rotating column of air in Tornado: a violently rotating column of air in

contact with the ground. Also called “twister” contact with the ground. Also called “twister” and “cyclone”and “cyclone”

Waterspout: a tornado over water, generally Waterspout: a tornado over water, generally much weaker than a tornadomuch weaker than a tornado

Funnel Cloud: a rapidly rotating column of air Funnel Cloud: a rapidly rotating column of air not in contact with the ground, often the not in contact with the ground, often the precursor to a tornado, extending from the precursor to a tornado, extending from the base of a cumulonimbus cloudbase of a cumulonimbus cloud

Tornado SafetyTornado Safety

Avoid blowing debris (don’t become a part of it, Avoid blowing debris (don’t become a part of it, either)either)– Get underground, if possible (wind speed = 0)Get underground, if possible (wind speed = 0)– Find a ditch or low spot and cover your headFind a ditch or low spot and cover your head– Interior, windowless room of a sturdy building, Interior, windowless room of a sturdy building,

preferably under something that won’t fall on you preferably under something that won’t fall on you but will protect you from falling/flying debrisbut will protect you from falling/flying debris

– Avoid cars and mobile homes, highway overpassesAvoid cars and mobile homes, highway overpasses

Tornado Tornado IntensityIntensity

The Fujita Scale: based upon damage surveys The Fujita Scale: based upon damage surveys and not direct measurement of windsand not direct measurement of winds– Similar to Saffir-Simpson scale for hurricanesSimilar to Saffir-Simpson scale for hurricanes– Ranges from F0 (EF0) for very weak tornadoes to Ranges from F0 (EF0) for very weak tornadoes to

F5 (EF5) for incredibly strong tornadoesF5 (EF5) for incredibly strong tornadoes– Scale goes higher (F12) but it’s unlikely we’ll see Scale goes higher (F12) but it’s unlikely we’ll see

anything stronger than an F5- how can damage be anything stronger than an F5- how can damage be any worse than “incredible?”any worse than “incredible?”

– The strongest tornadoes develop within The strongest tornadoes develop within supercellssupercells– Enhanced Fujita Scale

Supercell ThunderstormsSupercell Thunderstorms

Produce the most extreme Produce the most extreme severe weathersevere weather– Large, strong tornadoesLarge, strong tornadoes

Wind shear- direction, speedWind shear- direction, speed Rotating thunderstormsRotating thunderstorms

– Long (~6 hour) lifespanLong (~6 hour) lifespan Wind shear- direction, speedWind shear- direction, speed Tilted updraftTilted updraft

– Large hail and damaging windsand damaging winds Extreme instabilityExtreme instability Extremely strong updrafts and Extremely strong updrafts and

downdraftsdowndrafts

Supercells: Extreme Vertical MotionSupercells: Extreme Vertical Motion

The The LidLid (capping inversion) (capping inversion)– Warm, dry air overlies warm, moist airWarm, dry air overlies warm, moist air– Result of low-level S,SE winds from Gulf of Mexico Result of low-level S,SE winds from Gulf of Mexico

and SW winds above this layer blowing from the and SW winds above this layer blowing from the Mexican plateauMexican plateau

– Limits development of “wimpy” thunderstorms: more Limits development of “wimpy” thunderstorms: more energy available for a few supercells versus lots of energy available for a few supercells versus lots of run-of-the-mill thunderstormsrun-of-the-mill thunderstorms

Supercells: Extreme Vertical MotionSupercells: Extreme Vertical Motion

– Breaking the LidBreaking the Lid Daytime heating weakens itDaytime heating weakens it Rising air will cause a more rapid cooling aloft than near Rising air will cause a more rapid cooling aloft than near

surface: result is explosive thunderstorm developmentsurface: result is explosive thunderstorm development

Supercells: Long-Lived MonstersSupercells: Long-Lived Monsters Directional and Directional and

speed shear tilts speed shear tilts the updraftthe updraft

Separates inflow Separates inflow and outflowand outflow– Constant supply of Constant supply of

warm, moist airwarm, moist air

Supercells: Tornado DevelopmentSupercells: Tornado Development Directional shear induces thunderstorm rotationDirectional shear induces thunderstorm rotation Speed shear creates Speed shear creates horizontal rollhorizontal roll Roll tilts vertically in updraftRoll tilts vertically in updraft

Supercells: Tornado DevelopmentSupercells: Tornado Development

Strong updrafts and downdrafts, especially the Strong updrafts and downdrafts, especially the rear flank downdraftrear flank downdraft, appear to be important in , appear to be important in tornadogenesistornadogenesis– From Markowski et al, From Markowski et al,

2002, 2002, Direct Surface Direct Surface Thermodynamic Observations Thermodynamic Observations within the Rear-Flank within the Rear-Flank Downdrafts of Nontornadic Downdrafts of Nontornadic and Tornadic Supercells, and Tornadic Supercells, Monthly Weather ReviewMonthly Weather Review

TornadoesTornadoes Suction Vortices: think of them as mini Suction Vortices: think of them as mini

tornadoes within the primary funneltornadoes within the primary funnel Image from Image from www.atmo.arizona.edu/.../apr2609.jpgwww.atmo.arizona.edu/.../apr2609.jpg

Are tornadoes becoming more frequent?Are tornadoes becoming more frequent?

Key Figures Key Figures

Tables 14.8, 14.9, 15.8, 15.10, 15.12Tables 14.8, 14.9, 15.8, 15.10, 15.12 Interesting Time-Lapse Movie of Thundersto

rm Development Time-Lapse 2 / Time-Lapse 3Time-Lapse 2 / Time-Lapse 3 Multi-Vortex TornadoMulti-Vortex Tornado M-V Tornado from HelicopterM-V Tornado from Helicopter Rotating Supercells in Wyoming/TexasRotating Supercells in Wyoming/Texas What you normally should NOT doWhat you normally should NOT do